This really only explains the piston speed limit, though. In most cases, the actual limiting factor is valve float. For the bottom end, the limiting factor is ring flutter. If your piston changes direction too rapidly or your rings are too heavy, they lose their ability to conduct heat because they lose contact. They overheat and swell, which reduces ring gap. Once your gap hits zero, you seize and break stuff. Lighter rings and wider gaps can help you exceed the conventional 4k fpm rule. For the top end, the reciprocating mass of the valvetrain, aggressiveness of the cam profile, and strength of the valvespring determine the float RPM. This will usually hit before the bottom end RPM limit in a SBC because lifters and pushrods are so heavy.
Joe cook, Joe, what engine are we talks about? How many cylinders? Valve train design? Overhead valve overm? Has the rotating assembly been balanced to +/- 1 gram? If you have an oversquare engine you can achieve a higher piston speed before catastrophic failure. This will also depend on if your using cast or forged crankshaft.
Very good info. I've been asked many times, How do you know if you've over revved an engine. My definition is, localized pains in and around the left hip pocket and the realization that your engine will now fit loosly in a 5 gallon bucket. lol!
I am 62,,,been master tech most of my life. But I have to say I really enjoy ur videos. I'm thinking I learn something every time I watch one. I thought I knew everything about RAT motors cylinder heads. But I learned something from that video as well. Thanks,
I saw this video about a month ago. Great information. Thanks! HOWEVER.....I thought, "Where did the magical divisor of "6" come from and what is its unit of measure"? To go from inches to feet, you MUST divide by 12 (12" in a foot) not; 6. Then, it hit me last night. "Revolutions per minute". A revolution is a full cycle, both up and down of the piston. So....you really must add the stroke up to the stroke down. For the 302, it's 3"+3"= 6". Then, multiply by 7,000 RPM to get 42,000 inches of travel per minute. Now, convert from inches to feet using the divisor of 12. You get 3,500 Feet per Minute....not Inches per Minute. Yes, it's the same answer but, that's the correct way, in my humble opinion, to follow the units of measure. He used 6 (half of a foot) because he only used half the cycle (the up stroke). Now, why is 4,000 FPM the magical number? It seems to be factual but, why? I can't see my 1973 302 turning 7,000 RPM.
Believe it or not there is a rule of the thumb that requires almost no calculation at all. Some extrapolation is required as the rule of the thumb part only works for 6000rpm. So all one has to do is know the stroke length in decimal inches, add a zero to the end and voila! 3.00" stroke = 3000 fpm MPS @ 6000rpm 3.50" stroke = 3500 fpm MPS @ 6000rpm 3.75" stroke = 3750 fpm MPS @ 6000rpm I am confident the 4000fpm could be easily exceeded in small motors with low reciprocating mass. An example, for the road going Honda 250cc 4 cylinder Learner motorcycle - the CBR250RR has a 1.33" stroke (33.8mm) and can turn 20 000+rpms. So 1330fpm @ 6000rpm will equal 1330X3 which is 3990 fpm MPS @ 18000rpm (1330x3 as there are three sixes in eighteen - puts you in the ballpark of 20 000rpm. This is the extrapolation bit) I told a mechanical engineer of this and he scoffed. I taunted him to run the numbers which he did there and then and looked up in puzzlement at me and announced "You're absolutely correct." Your equation is ideal for knowing the exact mean piston speed mine is just a simple rule of the thumb one could apply to say talking to a customer over the phone. Great informative vid BTW :)
Awesome, thank you. I've asked all over the place for a max RPM on my Ford 400 that I'm building, I went with my gut of 5900 max with a stock bottom end (4" stroke) and hypereutectic pistons. With this calculation, 6000rpm is exactly 4000fpm. Subscribed, thank you.
Im slowly working through your videos,and i damn well wish i could actually buy you a few beers,because they are fantastic! I live in the UK,& us chevy lovers are few & far between! Im just considering putting a Gen 5 454 into my 1980 Z 28 Camaro.Thanks again for such great info & videos!
This might give you an idea of how old I am. When I was young I had a Nova that I played with. I liked the 283 over the 327, with low fives in the rear end I would run out of motor just before the traps. The 327's would not survive this treatment a couple of dozen times. Here's the age part, before all these fancy head I had double humps on the 283's. After each run I would pull the pushrods and roll them to see which ones were bent and hammer the studs back in the head from the rocker arms pushing them out. The 283's never reached the speed on the piston to destroy its self or throw the rod and the extra weigh from the 327's piston would grenade the rods. Your explanations over the last few weeks is the best example of why this happened. I really like what you are doing for the, shall we say less experienced persons like my self. Keep up the good work, and yes I grumbled to about the machine work. But the better it is engineered the longer it lives. BEST OF LUCK FROM SOUTH FLORIDA...
Aaaa yes I remember those days my first drag car was also a nova I built a 307 bored it .060 over and ran camel hump heads with a 310 duration Isky cam hooker headers and a big Holly carb I never had good power brakes because of the cam no vacuum booster! I know it sounds silly to build something like that now but at the time it was all I had and it ran pretty good for what it was I ran mid 14's all night long and never hurt the engine my gear was a 456 and I would hit 6200 RPM at the traps I've since had much faster cars and much more powerful engines but that 307 nova is somehow still my favorite car there was just something about Friday night drags back then lots of garage built Ford's and Chevy's, Pretty girls, and not an import within 50 miles those were the days thanks for this post you just made my day!
Myvintageiron7512 Wow that seems like the hard way to run 14's. My Nova has a rebuilt 350 (actually a 355) with 882 heads, dual plane aluminum intake, quadrajet, and a .435/.435 270 duration performance "RV" style camshaft that runs 14s with the factory 2.73 gears in it. Those gears also allow me to take it on the freeway unlike those 4.56s. Also runs in -10*F and +100*F ambient temps without issue. Oh and I still have plenty of vacuum for stop and go traffic ;)
well you see back then I didn't really know what I was doing and building a 307 was proof of that the thing is I was 17 and I honestly think I had more fun with that car than any other car I've owned or built even though I moved on to much bigger engines and serious drag race cars The Nova was my first and there is just something about the first time.
Myvintageiron7512 The best way to learn is through experience! I also here you about the first time. I made the mistake of just bolting on a single plane intake manifold and mechanical secondary 4 barrel carb on the inline 6 in my first car. It was impossible to tune. Sometimes it would shoot off like a rocket but often it would bog, never could get it to run quite right. But when it did go my little four door could blow the doors off 5.0 mustangs and most older fbodys through the 1/8mi. I've learned from my mistakes and that's why my Nova has a dual plane (Weiand) intake and a vacuum secondary carb (quadrajet). Ok, so there was a lot of engine building theory studying going on between then and now too. Keep up the great work on this channel! You've been verifying I built the motor up in my Nova correctly. I'm looking forward to hearing this stroker motor run.
@@Myvintageiron7512 Yep, I was drag racing at 20 years old in my own car. I left home at 15, got myself a job at the local garage and never looked back. It was 40 years of automotive. I'm still mad at myself for not building a serious Nova.
This video and the one covering camshaft selection are priceless additions to my future engine build. I was given an LS1 from an '98 Camaro and want it to both make good TQ/HP numbers but also give me half decent mileage. I know you can't have both high peformance and high mileage, but there is a sweet spot one can achieve w/ careful planning. Its going to be a challenge w/ the lack of bore-ability of the block, but I should easily be able to hit the milestone of one HP per C.I. w/ a proper balance and assembly. My goals are maximum torque while maintaining emissions compliance, as its my daily driver.
I really like your videos; A++. They are packed full of information. I hate going to watch a video for information, and the guy takes up half the video watching him eat breakfast, and then going to visit his Uncle Bob.
thanks to reducing equations we can simplify (r*s)/6=4000 for the purpose of finding a target redline speed into 24000/s=rpm so simply divide 24000 by your stroke in inches to get the exact redline rpm.
Exact stroke for max rpm of 7000 is 3.4285. What's cool is I just got my hands on an engine only made for 4 years 5 if you want to get technical. The stroke on this 383 is 3.380. So I have 0.048 to work with. Gets me thinking about the engineers and what they were really after. How about something that can be mass produced for intended use but, with a little modern (modern being used broadly, modern is just the time) technology for final touch up work. Can just sit happy right where a street RPM band engine should be for a V-8.
The issue is most production V8's are cammed/intaked to make power between 2-5k, after that they fall flat. If you change an engine to make peak power 5-8k customers would think its too sluggish or too much power pickup in the top range making it dangerous for inexperienced drivers. Its a tradeoff they had to choose reliability and fuel consumption rather then power
Ariel Lezen So since the tach is driven by the cam, every cam rotation the distributor tells the tach to double the amount of revoltions because the crank is 2x the speed of the cam ?
You just earned yourself a subscriber. Awesome video man. There is a lot of information in this video, but it's not spoken like it's being read from a book. It's broken down into "laymens" terms and it allows almost anyone to understand it. Awesome video.
Very good video.....good explanations. I used a 350 Chevy for brackets back in the day with a built motor...good rods, crank, forged pistons, ported heads, bigger headers, good collectors with open exhaust, 5:56 gears, etc. Depending on track conditions I used Victor or aluminum Corvette/Edelbrock 180 degree intake..... If I recall I used a 30-30 Duntov with solids.....it was a good cam because I could open or close the clearance to vary how "big" the cam would be. I would run about 7000 rpm and go thru the eyes at 7200. It held together forever but I watched the tach like a hawk. The car was not licensed for the street. I guess I could have been more radical but this was before all the aluminum heads, etc came into being. I think in those days we understood more about how enginces, etc worked because we HAD to figure it out for ourselves with the machinist. Today, guys can open their wallets with little knowledge and end up with a pretty good engine.
When I was younger my dad built a 351W with Cleveland heads, and he swapped over to a solid cam, adjustable valvetrain setup with a lumpy cam. He always told me that a 351 could pull 7000, but I really wasn't sure how that was possible since the 4 cyl in our Focus barely did 7000. Now that I'm following suit and getting into cars, and that I have more knowledge, it's easy to see how to squeeze revs out of an engine. As always, well explained video.
+Ryan Eyster A 351W will turn 7000 it is feesable to go above the piston speeds I have laid out race engines do it all the time you just need stronger internal parts and a much better balance job 4000 FPM is a good safe max piston speed for a stock engine
The Cleveland will do 7000 more reliably because of the smaller crank journals. One of the other things that affects the rev potential of an engine is its ability to reliably supply oil to the journals, and larger journals require a better oiling system to supply enough volume due to the cast-off created by higher surface speeds.
ThePaulv12, no, the Windsor is a wedge head engine, like the 302, that was never as popular for performance as the Cleveland. The Cleveland is a canted valve head, like the big block Chevs. It also has a shorter deck height and smaller main bearing diameter than a Windsor. A 2bbl Cleveland had heads that were more than adequate for most street and racing, but, the 4bbl heads had huge ports that are said to outflow a 427 rectangular port Chevy. These were the same heads used on the Boss 302 and had a very high rev capability due to the flow.
Good day I am looking forward to rebuilding my 4.0l Jeep motor this summer. Following the formula to figure out my RPM I should be able to build my motor to match the drive train. Thanks for the information and the simple way of explaining things.
my 409 and 348 both topped out at 4300 RPM. 327-375hp slightly built about eight. But no matter what an engine was rated for I usually drove by ear and feel. Great video's, thanks.
You're missing the reason for the longer rod!! You understand the higher RPM and stroke reasoning, but the advantage of the longer rod is entirely geometric! A greater advantage is achieved with a longer and more angular focus on the crank increasing the leverage and advantage!
He didn't miss it. All he was talking about was the components and if they can take the speed you are wanting to spin the engine to. The advantage means dick if the internals can't take the forces and become separate pieces.
Here is an interesting fact you may not know. The piston moves faster closing in on and moving away from the top of the stroke versus closing in on and moving away from the bottom of the stroke. The reason why is because of rod angle effectively acting like it's growing the rod in length as it approaches TDC and in effect shortening in length as it draws away past TDC. The distance between crank throw and wrist pin varies with the angle of the rod. Growing in length while approaching BDC, bottom dead center actually slows piston speed down. It may be hard to fathom but the net effect is that there is more dwell time at the bottom for cylinder filling and less dwell time at the top to take advantage of chamber pressure. Learned this phenomenon at the tender age of 70.
Hmm, with this formula, the Olds 350 and 403 appear to have a slight advantage over their Chevy cousins with the same cid. The 350 rocket is a highly under estimated engine. Early 350 rockets can be bored to the 4.125 bore the 425 and 455 share, but have a 3.385 stroke, They can also use the big block heads as a upgrade. Even with windowed mains, the 403 can produce some insane numbers.
I've seen dirt track racers consistently run 350 Chevy's with stock bottom ends to 7000 RPM but on a few drag race cars I've always played it safe to 6500. Had a 396 once that I would turn to 6000 RPM. But I'm a cautious guy. Great video and thanks for explaining the numbers.
I have a friend randy that built a Chevy small block back in the late 80s that saw the far side of 8700 rpms and that thing was a beast, it never came apart , it was in a 69 Camaro, I saw that car beat built 600 hp big blocks , one guy he raced and beat said i heard the horse power screaming out of your grill when you passed me
Until I had watched your video I had naively assumed that the connecting rod length was almost entirely a side load issue. I had not realised that it also had an effect on dwell time.. you are right of course. It is a shame that people don't always pay proper attention, I cannot fault the information you provide. I think that rather than disputing the facts people should perhaps watch the video a second time, well done on a well put together video.
Equation works! My mercury v8 outboard has a stroke of 3.4in, so that means theoretical redline of 7000. Factiry redline is 6200, but the "race" version is 6500.
Great info that is data based. This equation takes the guess work out of what people assume is safe. Great articulation and explanation. Great job on the video. Thanks for taking time to offer this research.
Strong internals go a long way here. 4340 crank and fully forged pistons and rods @ 4.25 inch stroke hasn't cared about 7500 rpm in my little hotrod...Yet... Pettis performance builds 598 Chevy (race motors) with 4.5inch stroke that make peak power at 9k. Very informative video!
With this math my Olds 403 could rev to 7,000 rpm. Unfortunately the weak windowed block can handle that. Kinda wish I went for the full monte J&S Halo girdle (did install the 4 main girdle) I'll keep it to 5500 and less and hopefully I don't blow the thing to bits. The 403 bore stroke ratio theoretically is great for a high revving engine, but the block strength holds it back.
Would be cool if you did a video on the effect the connecting rod length to stroke ratio has on the hp and torque of an engine. I've always wanted to build a Bug engine with a 1300 crank and the biggest bore pistons the bore centers would support and then have the cylinders long enough to support 2.3 x stroke ratio. Billet heads with the biggest valves that would fit without shrouding in the bores, and as close to a 14:1 compression ratio with closed chambers and D cup pistons. The camshaft would be tuned to the dwell time of the pistons at the top of the bore. The next thing would be a single plane pyramid intake with a tuned plenum and runners along with a Holley 660 center squirter carb. I know the Euro guys like the weber carbs for throttle response, but a single plane intake with a combined tuned exhaust makes more power overall.... Anyway, would be fun to build such an engine.
+Ray Main You're even getting me excited. Remember high compression = pumping loss. There have actually been a number of very high compression production engines over the years and after the first run they were always backed down to around a still high 11:1. Another thing, by my way of thinking, very high compression is only worthwhile (on the street) if the ignition timing is
That is why I love the 302 Engines because they are Short Stroke Wide Bore and you can wrap them out even stock I nailed 5500RPM in my Bronco few times and it felt smooth at that high RPM Also Short Stroke wider bore engine have much better Throttle response in my Opinion.
R.P.M's, i knows MANY mechanics/technicians use plural on minute. I have 2-96 Roadmasters with the LT1 cast iron head, I have no idea of the casting numbers but 2000 R.P.M's with the rowing package gets me 80 MPH all day. I bought one of those tuners to tweak dis n dat and raised the governor from 108 to lotz more and put higher speed rated tires on one of them and now I've been to 3500 R.P.M'$ which is/was north of 130 M.P.H'$ on highway 99. Built a few engines and enjoyed the few videos of yours I've watched. Gene from the left coast near the state Crapitol
Not to mention, bearing surface speed with longer stroke requiring a better oil delivery to cool the bearing surface. With oil temperature being more critical to making power, the window narrows significantly. The old rule of 10 psi per 1000 RPM may not be sufficient.
It's really a function of thermodynamics and friction...with the mechanical design being adapted to address the dynamic metallurgical structural weaknesses (a multi degreed Aerospace Engineer who works for a large American defense contractor.
Thanks, this was a great explanation on how to find an engines recommended redline and performance capabilities. As a side note what is the stroke length of a 5.3L LS engine or would a 4.8L LS engine possibly be a better option? I would like to use a M122 GT500 Roots style supercharger and possibly even use a turbocharger as well.
Now that was informative thanx bud. Ive got a 355 Id say a lil bit more than moderately built .i twisted it to 7500 and 3 of my harland sharps started clacking pulled covers off and had 3 backed off to abot .050 .supposed to be .021 wp heads,1.555 springs,doubles with dampers. Cam .600 in .625ex..rockers actuall hit stud girdles.ALMOST A CATASTROPHIC.
Great video, I have a 2003 Toyota Matrix XRS which has a 2ZZ-GE engine that red-lines at 8200 RPM with a stroke of 3.35". By your formula my pistons are traveling at ~4575 FPM. But I guess that is what you do when you are a large corporation and reuse and engine that you put in a Lotus Elise/Exige.
I just calculated a few for comparison: 1) bmw 330ci: 3173.3 ft/min 2) Honda S200: 4960.6 ft/min 3) Yamaha R6: 4870.8 ft/min 4) 2010 Formula 1 4724.4 ft/min *I think some factors that play into RPM are: - reciprocating mass - secondary and primary balance - airflow at high RPM - stroke vs bore
Oh for sure the weight of the rotating assembly is key we like to use 4000 max for stock engines it's really safe but certainly not something that can't be surpassed
Thank you for your Chevy 350 Video Series. These videos have helped me improving my technical understanding of the 350. Im saving up for my first engine Rebuild or Engine Build right now. ....Best Case scenario.... I'd LIKE to see 600 hp/ 550 Torque out of my current 350. either in the 383ci or 400 ci. but since I still need to iron out other details on the truck. I'm probably just going to do a HO 350 rebuild for now. so I can drive it while I get the other details fixed as I go. I'm considering buying a built crate Engine or sourcing a LS Engine later. the problem I have with the LS Option is. all the little stuff im going to need in order to make the LS work in my 94 S10. Wiring. Engine Mounts. power train. Computers. transmission linkage. cooling systems. yada Yada yada.
I have a 92 S10 myself. As well as a 1970 350/300 4bolt along with a good 350TH to use if I wanted. Same problem as you. The LS option is for sure going to require extensive wiring and what the heck, the speed it is going to generate might as well figure in a suspension as well. Lord knows the flimsy shocks that you get for the S10's isn't going to handle the corner speeds... I'd like to do anything/everything to the 350 and sit it in it, but hate to think that it will be just a putt putt truck...
@LORDdeath Gaming You're making more out it than necessary for an LS swap. The wiring is a simple affair that you just lay on top of the engine, once installed, and start making connnections - it falls together like falling dominoes. I was intimidated by the prospect as well, but it went quite smoothly, once I hunckered down and started the process. As for your plans for your SBC, just remember speed costs money, so get rready to spend a pretty penny for an engine w/ those specs. Just sayin' those are big block numbers. Best of luck.
Here are some basics: factory built engines are usually only harmonically balanced to about 5000 rpms. The first thing I do with an engine build is called "balancing and blueprinting", where the crankshaft is harmonically balanced by the machine shop to 10,000 rpm without vibration. Then we "blueprint", this involves weighing all of the piston/rod sets, and we find the lightest one. They never weigh exactly the same, and that's what we want: we grind a bit off each one until they all weigh exactly the same as the lightest one. Now you have a bottom end that can take huge revs without shaking itself to death. The limiting factor, now, is the strength of the valve springs, and their ability to close the valves fast enough. My old Suzuki GS1000 floats the valves with the stock springs at 12,500 rpms. "Floating" is when the springs can't close the valves fast enough, and they sort of just float open. All of a sudden the engine will just crash, and loose all power at a certain rpm. If I put heavy duty springs in, I could get around 14,000 before they float.
Your butt is sucking pond water on your basics. How is the crankshaft balanced to 10,000 rpm when the balancing machine only spins the shaft at 500 rpm? And how did they balance the crankshaft without first equalizing the weight of the pistons and rods to make bob weights--unless you're talking about a 4 cyl or straight 6.
I got a small block Chevy 327 , it has 12:1 forged pistons , steel Vette crank in a 4 bolt main block , It cranks 11,000rpm before the valves start to float
I was just watching you talk about this subject in your new How To Pick A Cam video and it seems like it would make more sense to pick a piston speed and calculate for RPM. With a desired piston speed of 4000 and a stroke of 3.5 inches it would look like this 4000 X 6 = 24,000 ÷ 3.5 = 6,857 Then you just round down to the nearest hundred just for safety, 6800 is the right RPM. If I'm wrong let me know.
Cool information my stroke is 3.6 so it seems as 6500 is the max safest rpm I can go on my engine which is 3900 fpm. And you said the longer stroke gives more torque which is interesting as I could tell my engine was a lot more torquey than my 3800 L36 powered car which according to this formula the L36 can easily do 7000 rpm and would probably max around 7200 rpm which gives me 4080 fpm on that engine. This video made me subscribe thanks for the info.
I am spinning a 4.6" stroke at 7400 RPM. But as he says, much must be done to be strong enough to do it. Billet crank, rods and main caps to start. This is in a one off tall-deck LS race block. (LS blocks have fully girdled main caps unlike SBC, so that helps too) But that give you an idea of where things can be taken if you want it bad enough.
351cleavland usually the failure of the end cap or connecting rod bolts ... i.e. ..flies out .. other sources of failures can contribute too .. lack of oil psi to the bearings , cause the bearing to fail .. excessive clearance leads to the "knocking " then excessive heat , gaulling , seizure , boom ... the rod is the last to get oil ..
randysengine service Sure, I did that and a week later a piston flies out the engine compartment into the cabin and up and out through the sunroof! I am 50% sure its not going to bre covered by warranty!
He uses a 6 so it's easier to calculate piston speed. There's two stokes in one rotation of the crank so the stroke needs to be multiplied by 2. Then to get feet per minutes you need to divided 12. So essentially your dividing by 6. Stroke x 2 x rpm / 12 = fpm
Very informative especially for someone who is not a mechanic, but I have a question- If I have a neo vvl St 20 will installing a vvl controller and setting it before 5000 rpm harm the engine? Thanks
i've just seen the video and after doing the math the results are!! my car chrysler SRT8 HEMI 6.1L after few upgrade now it has 4.250 strok 4.125 bore CNC heads etc.... also it is my daily use car and with 3.73 diff the RPM is always high and 6500 RPM is a number that i reach as my daily routine if you do the math: 5650 rpm × 4.250 ÷ 6 = 4002 FPM what about 6500 rpm its more than 4600 FPM dyno test is: 510+ rwhp on gas pump
I had a roommate in the early 90s, with a mildly hot rodded 350 in a '64 Chevy II. He had a very safe and logical method of determining red line, which required no pesky mathematics. He simply kept revving the engine til shortly after it stopped making noticeable power anymore. On a 100% completely unrelated note, it spun a bearing 2 months later......
Due to rod geometry, the fastest piston speed is usually in the top 1/3 of the cylinder. In the center of the cylinder, the piston is starting to decelerate as the crank comes the 90 degree point, actually starts decelerating at about 60 to 80 degrees, and decelerates the most as the journal starts to swing back in the bottom half of the stroke, stopping again at BDC. Also, a short rod engines like the Ford 302W or Chev 400 small block have faster acceleration away from TDC, once again due to rod geometry, than a longer rod engine, like the Ford Boss 302 or Chev 350, which can cause a piston to pull apart easier at the same RPM.
That depends on rod/stroke ratio Most engines peak out at dead middle of the stroke Engine with short rods and long stroke will have 2 peak pistons speeds near 1/3 down and 2/3, but actually slow down some in the middle of the stroke. that's because rod angularity accelerates the piston against the cylinder wall, but this increases runner air velocity and can be used to increase volumetric efficiency Peak piston speed at redline for a 5.0L is 82.5, while LS3 is around 72mph
The rod/stroke ratio will dictate piston accelerations and decelerations, but geometry dictates speeds in any part of the cylinder. Short rod will have quicker acceleration/deceleration, but, as the crankpin nears the halfway (90 degree) of stroke, piston speed starts to decrease as the rod angle change slows, no matter what rod length, usually around roughly the 30 - 45 degree range of stroke which has the piston in the top 1/3 of the cylinder. A shorter rod may have the piston farther down the cylinder, but not usually at 1/2. The difference between short rod, such as a 302 Windsor and longer rod, like a Boss 302, also dictates the cam requirements of an engine. Shorter rod engines like fast valve opening and higher lift at TDC to make use of the quicker piston acceleration away from TDC. Also makes use of larger carbs, valves and ports to allow less restriction to airflow acceleration as the piston moves from TDC. An easy way to study rod length on piston movement is to make a 2-d cardboard replica of a crank and cylinder. Make a circle to show the crankpin rotation and use a ruler for the rod. Pick points around the crank stroke and then match the ruler to the centre of the cylinder at different lengths from the same point in the stroke. You will see how the piston is higher or lower in the cylinder as rod length changes. The fun thing with this is that you can use rod to stroke ratios that would be impossible in real life to exaggerate the results and get a very good indication of how they affect each other.
Been a auto Tech for over 60 years graduated in 1968 from Lincoln Tech Back in 1970 bill Jenkins brought his Vega to the nationals a 400 Small block with A327 Crank Which worked out 332 cubic in Big bore short Stroke makes a killer motor They laughed at him at the end of the meet he put all the hemi's on a trailer
@myvintageiron7512 You do a great job explaining how things work! Your videos are the best. I wish Google would link to more of your info in the search results.
just an educated guess but the reason why you use 6 instead of 12 to go from inches to feet per minute is because the piston travels the length of the stroke twice for every revolution . so really what you are doing is ( stroke/12 ) x 2 which is the same thing as dividing it by 6
Great explaination. Just hope you can tackle cam design for the other unemformed some time, especially the part on advertised duration (SAE measures @ .004, where Crane Cams measures their cams), Comp Cams ( at .006s), and others and how this affects actual cam duration and how this affects power.
Could you add what would help turn more rpm I build alot of dirt track engines in many classes alot of people need to understand what helps engines live at rpm , great video thank you .
Building my Harley Engine for the 3ed time , I set my Over Rev limit to 5500 RPM now your video has me thinking I could go to 6500 , Each time its been my fault it has blown, Bad lifters, bad cam bearing, then a bad pushrod .
old man bell built me an engine that is nuts after he built it he told me this engine will do 10,000 rpms all day long so we had to test it we took it up to 15,000 rpms many times racing it and we run pump gas only running 13 to 1 compression with no problems no pinging or any thing it just ran hard just one problem with it like to rev real fast with water pump alt and power steering could not keep up and it will twist the front part of the crank right off but the class we were racing requires to be street legal has to have all the stuff to drive on the road and no stripping the car down so i had to learn not to rev it to hard but we never lost a race in my area but far from being cheap to build bell said he did everything he could on a sb even season the engine for a year and polished the inside of the block started with 202 angle plug heads but bell did his magic to them too , stock headers will not fit no more how he described the engine was a indy bottom end with a dragster top end he said this way u can run real low gears and not lose top speed and u can gain torque thew the gears . i really could not believe this engine even when i was racing it the rpms was insane the sound that it made would make any man cringe just screaming sound i have a lot a race engines but this one is special next i am building a bb chevy because i just got a set of hemi heads for bb chevy of a funny car for 300 bucks
Sort of off subject but could you explain briefly the designation of Chevy engines. I see references to LT1, LS, Gen1, Gen2. Pretty confusi g when looking for parts.
Reliability/durability of the crank and bearings are what limits rpm, right? They the failing components of high rpms, right? Can you increase rpm and/or add stability/reliability to the exicting redline by using a higher viscosity oil or some kind of racing oil?
Great video. Not sure where the 4000 fpm number comes from, but definitely gave me something to consider. I used your equation in reverse to determine the theoretical redline on my Buick 455: ((4000 fpm) x (6 factor)) / (engine stroke) = (theoretical redline) (4000x6)/3.9=6,150 rpm. 👍
yeah I wouldn't run a 455 to 6,150 for very long though, the oil system just won't doesn't support prolonged revs. The Buick, Olds and Caddy engines suffer from pumping oil to the top end and not draining back to the pan resulting in bearings not receiving adequate oil. This can all be "fixed" but be careful in a stock application.
What I was hoping would be covered in this video was the effect of longer rods on the same stroke...I've seen a lot of guys build "long rod" engines, but are the gains worth the time and effort? I've also read that long rod motors make much better use of small valves and ports, but I haven't come across very many A-to-B comparisons.
Between 70 to 80 crank degrees on primary stroke which is tdc to bdc that's its fastest speed.and between 2 to 15 degrees past tdc is highest pressure in chamber.
There are so many parts available for the SBC that its bery hard to figure out the correct combo. Can you do a video for a 600 HP Chevy 350 build? Plus can you explain how to tell if the block is high tin/ nickel. I have a 350 4 bolt main, bored to .060 over with a .120 cylinder walls, behind the timing gear is has 10 and 20 molded into block. Someone told me that means it is a high tin and high nickel block. Is this correct? P.S. I will be using AFR 220 (2.08/ 1.6) heads. I will be driving it on the street, but I want it to sound like a Pro Mod when it idles. Thanks for your help and love your vids.
great video, came at a really good time, I am putting my 283 short block together soon. really want it for a RPM grabber for no good reason at all, just to have fun with... I am deciding on heads, I have flat top forged pistons, stock rods with ARP bolts in them. Q: stock heads fully ported( non humps) or newer style "vortec" head (305ci) or something else. any advice would be awesome, thanks!
I have video of the 283 with vortec 350 heads and I loved it but they ended up being cracked and that is why I am redoing it. just looking professional advice as I am about 35 years old and this is the first 283 I have messed with. thanks
I didn't learn this in feet / min, I come from a metric country (Australia), and we do this in m/s. But over time the maximum recommended piston speed has gone up from about 12 m/s when I was a kid, to about 16 m/s now. It's also worth going over rod length to stoke ratio. I would also mention that engineers at the factory do their calculations, but then they do a practical test. They run the engine on a dyno at about the maximum power for a time (hours, not seconds) and then strip and inspect. When I was a kid, in the '70s, Honda was supposed to run any production engine at redline for a week. If the engine suffered serious wear or damage in that time, the engine spec was changed or the redline was lowered.
+Kneedragon1962 Also maybe mention, there should be a natural safety margin between max power rpm and redline. One real criticism of racing engines is the ones that are still gaining power (or sometimes even torque) at redline. They're difficult things to use safely, for a number of reasons. Instinct and the seat of the pants will tell you to keep it pinned because everything is going great...
Well yeah. Nascar was turning the 358 ci. Fords and Chevy's 6800+ way back in the early 80's. True they didn't have the parts we have today, but they were doing a lot with cast iron cranks and stock rockers... And yes, they did blow a many engines as well...
hi great vid , does this same rule apply to the 366 gm big block truck engine ? or are all stock engines built to a certain standard or envelope that all stock engine engineering fall into ? .the reason i ask is because the 366 has extra heavy 4 ring pistons and planing to build one for towing , redline under 5500 rpm , Thanks
I like your videos! been pushing your numbers around according to these numbers I could push my 6.6l duramax with a 3.9 stroke to 6150rpm! I wouldn't do that I'm sure somthing would let loose way before this! perhaps the 4000ft dosnt apply to diesel applications?
Good video but, connecting rod length does not affect piston speed or piston dwell. It does however greatly affect sidewall loading and force on the crank. Particularly during the combustion stroke, where most connecting rod failures occur. The longer rod reduces both sidewall and crank fatigue but increases rotating weight and to avoid over-compression, the wrist pin location in the piston must be moved up creating longer skirts which weakens the piston itself.
you are partly right and partly wrong rod length does not change average piston speed that is true however rod length does change when and how the piston speeds up and slows down also rod length most definitely does effect dwell time anyone who has degreed a cam with different rod lengths know this
@@Myvintageiron7512 I wasn't trying to be argumentative or condescending however, you are wrong. A shorter rod increases the angular reference to the piston wall which causes the piston to accelerate and decelerate faster as the rod reaches parallel TDC and BDC. As you said, the average speed does not change, acceleration just moves further from center of the stroke and closer to TDC and BDC. At TDC, the rod is perfectly parallel to the chamber. The piston stops moving roughly 1 degree from top center so you have right at 2 degrees of little to no movement. The distance from the crank to the wrist pin does not change dwell time however the circle of rotation (I.E. the stroke) does. A larger circle takes more distance to travel 2 degrees and therefore more dwell time. Now for your last statement.... Anyone who has degreed a cam regardless of rod length knows to set their piston stop a few degrees short of TDC to find perfect center and isn't worried about so called dwell.
yes I agree you don't really worry about dwell when degreeing what I was getting at is you can see the difference in dwell time with a dial indicator on the piston and a degree wheel on the crankshaft use the same cam and check the crankshaft movement with a 5.7 rod and then check it with a 6"rod the crank will move more degrees with no piston movement with the 6" rod than it does with the 5.7 rod IE more dwell time
I don't understand why the piston travels faster if it has a longer stroke. To me it appears, according to your formula, that the speed(rpm) is remaining constant but the distance covered is increasing with stroke. The stroker is not traveling faster but moving further therefore momentum plays a bigger role. What am I missing?
I was getting 7 grand shifts out of my 68 327 Camaro until the drive shaft came through the floor board. And that was with points not electronic ign. A 4speed trans and 3:08 rear.
I believe the piston is traveling fastest when the crank journal is at a 90° angle to the the cylinder bore. As it approaches the top and the bottom of the bore it slows down as it stops. The cranks rotary motion is at a controlled speed. Controlled by the reciprocating mass and the mass of flywheel and other engines components so it cant just takeoff freely on the power stroke. Its being governed so to speak by the compression strokes of other cylinders ect. The problem in keeping an engine together is the quality of the parts when the piston changes direction at the top and bottom of the stroke. The crank at the top of the stroke as it changes direction "yanks" on the rod and piston pin. Poor quality parts or a part with an defect or too much mass can be damaged.
The inertia of the rod accelerating in the each direction can cause the rod bolts to try and stretch as well as the beam portion of the rod. Moral of the story for lower end reliability use as long of a rod and light a piston combination as you can get away with while using ARP rod bolts. Another factor is minor and major cylinder wall loading this can be critical in Ford engines like the FE and Cleveland series which are both known for very thin cylinder walls.
Im 53 and been a mechanic most of my life. I`ve learned something new again.
Same here.
Just an outstanding series if videos.
63 : physically retired, THE day you do not learn something is a wasted day. MY personal motto that I live by .
really?
red line has different things, not only piston speed.
@Randy Wiesendanger until you learn that the word "cannot" and "can't" are not actually words at all.
@@jamessmith489 I have wasted many days as a trucker.
This really only explains the piston speed limit, though. In most cases, the actual limiting factor is valve float. For the bottom end, the limiting factor is ring flutter. If your piston changes direction too rapidly or your rings are too heavy, they lose their ability to conduct heat because they lose contact. They overheat and swell, which reduces ring gap. Once your gap hits zero, you seize and break stuff. Lighter rings and wider gaps can help you exceed the conventional 4k fpm rule.
For the top end, the reciprocating mass of the valvetrain, aggressiveness of the cam profile, and strength of the valvespring determine the float RPM. This will usually hit before the bottom end RPM limit in a SBC because lifters and pushrods are so heavy.
Thank you for this!
Accelerate until catastrophic failure, then reduce RPMs by 11.7%.
Hey what do you know, it works!!! 🤔🤔🤔
Absaalookemensch, I always built my engines with a rotating assembly that wasn’t the limiting factor. I used valve float as the redline.
I did it, but I'm struggling to only reduce engine speed by 11.7 percent. Suggestions?
Joe cook, Joe, what engine are we talks about? How many cylinders? Valve train design? Overhead valve overm? Has the rotating assembly been balanced to +/- 1 gram? If you have an oversquare engine you can achieve a higher piston speed before catastrophic failure. This will also depend on if your using cast or forged crankshaft.
@@arttafil6792 haha it was just a joke man just having a laugh
Very good info. I've been asked many times, How do you know if you've over revved an engine. My definition is, localized pains in and around the left hip pocket and the realization that your engine will now fit loosly in a 5 gallon bucket. lol!
Lmao!
When the Gremlins start playing death metal in the oil pan. You will know.
Didn’t Richard Petty say: we had an oil pan failure at 6800rpm
I am 62,,,been master tech most of my life. But I have to say I really enjoy ur videos. I'm thinking I learn something every time I watch one. I thought I knew everything about RAT motors cylinder heads. But I learned something from that video as well. Thanks,
Glad to hear it
I saw this video about a month ago. Great information. Thanks!
HOWEVER.....I thought, "Where did the magical divisor of "6" come from and what is its unit of measure"? To go from inches to feet, you MUST divide by 12 (12" in a foot) not; 6.
Then, it hit me last night. "Revolutions per minute". A revolution is a full cycle, both up and down of the piston.
So....you really must add the stroke up to the stroke down. For the 302, it's 3"+3"= 6". Then, multiply by 7,000 RPM to get 42,000 inches of travel per minute. Now, convert from inches to feet using the divisor of 12. You get 3,500 Feet per Minute....not Inches per Minute.
Yes, it's the same answer but, that's the correct way, in my humble opinion, to follow the units of measure.
He used 6 (half of a foot) because he only used half the cycle (the up stroke).
Now, why is 4,000 FPM the magical number? It seems to be factual but, why?
I can't see my 1973 302 turning 7,000 RPM.
Interesting technical advice, after tinkering on engines all my life I always wondered how engine manufacturer's calibrated an engine's redline.
Believe it or not there is a rule of the thumb that requires almost no calculation at all. Some extrapolation is required as the rule of the thumb part only works for 6000rpm.
So all one has to do is know the stroke length in decimal inches, add a zero to the end and voila!
3.00" stroke = 3000 fpm MPS @ 6000rpm
3.50" stroke = 3500 fpm MPS @ 6000rpm
3.75" stroke = 3750 fpm MPS @ 6000rpm
I am confident the 4000fpm could be easily exceeded in small motors with low reciprocating mass. An example, for the road going Honda 250cc 4 cylinder Learner motorcycle - the CBR250RR has a 1.33" stroke (33.8mm) and can turn 20 000+rpms. So 1330fpm @ 6000rpm will equal 1330X3 which is 3990 fpm MPS @ 18000rpm (1330x3 as there are three sixes in eighteen - puts you in the ballpark of 20 000rpm. This is the extrapolation bit)
I told a mechanical engineer of this and he scoffed. I taunted him to run the numbers which he did there and then and looked up in puzzlement at me and announced "You're absolutely correct."
Your equation is ideal for knowing the exact mean piston speed mine is just a simple rule of the thumb one could apply to say talking to a customer over the phone.
Great informative vid BTW :)
This is actually pretty good! I'll remember this forever, without even trying. Thanks for sharing it👍
Another method which is very simple. 24000 / stroke = redline. (This works if you are aiming for a 4000 feet per minute max)
You should not use the term "rule of thumb" if you knew the history behind that "saying" I dont think you would say it. I do not.
@@DavidStirm I wish someone would use the rule of thumb on you and beat that politically correct nonsense out of you...
That was the best most informative video I've seen on TH-cam. Thank you and keep doing what you're going
Awesome, thank you. I've asked all over the place for a max RPM on my Ford 400 that I'm building, I went with my gut of 5900 max with a stock bottom end (4" stroke) and hypereutectic pistons. With this calculation, 6000rpm is exactly 4000fpm.
Subscribed, thank you.
Im slowly working through your videos,and i damn well wish i could actually buy you a few beers,because they are fantastic! I live in the UK,& us chevy lovers are few & far between! Im just considering putting a Gen 5 454 into my 1980 Z 28 Camaro.Thanks again for such great info & videos!
This might give you an idea of how old I am. When I was young I had a Nova that I played with. I liked the 283 over the 327, with low fives in the rear end I would run out of motor just before the traps. The 327's would not survive this treatment a couple of dozen times. Here's the age part, before all these fancy head I had double humps on the 283's. After each run I would pull the pushrods and roll them to see which ones were bent and hammer the studs back in the head from the rocker arms pushing them out. The 283's never reached the speed on the piston to destroy its self or throw the rod and the extra weigh from the 327's piston would grenade the rods. Your explanations over the last few weeks is the best example of why this happened. I really like what you are doing for the, shall we say less experienced persons like my self. Keep up the good work, and yes I grumbled to about the machine work. But the better it is engineered the longer it lives. BEST OF LUCK FROM SOUTH FLORIDA...
Aaaa yes I remember those days my first drag car was also a nova I built a 307 bored it .060 over and ran camel hump heads with a 310 duration Isky cam hooker headers and a big Holly carb I never had good power brakes because of the cam no vacuum booster! I know it sounds silly to build something like that now but at the time it was all I had and it ran pretty good for what it was I ran mid 14's all night long and never hurt the engine my gear was a 456 and I would hit 6200 RPM at the traps I've since had much faster cars and much more powerful engines but that 307 nova is somehow still my favorite car there was just something about Friday night drags back then lots of garage built Ford's and Chevy's, Pretty girls, and not an import within 50 miles those were the days thanks for this post you just made my day!
Myvintageiron7512 Wow that seems like the hard way to run 14's. My Nova has a rebuilt 350 (actually a 355) with 882 heads, dual plane aluminum intake, quadrajet, and a .435/.435 270 duration performance "RV" style camshaft that runs 14s with the factory 2.73 gears in it. Those gears also allow me to take it on the freeway unlike those 4.56s. Also runs in -10*F and +100*F ambient temps without issue. Oh and I still have plenty of vacuum for stop and go traffic ;)
well you see back then I didn't really know what I was doing and building a 307 was proof of that the thing is I was 17 and I honestly think I had more fun with that car than any other car I've owned or built even though I moved on to much bigger engines and serious drag race cars The Nova was my first and there is just something about the first time.
Myvintageiron7512 The best way to learn is through experience! I also here you about the first time. I made the mistake of just bolting on a single plane intake manifold and mechanical secondary 4 barrel carb on the inline 6 in my first car. It was impossible to tune. Sometimes it would shoot off like a rocket but often it would bog, never could get it to run quite right. But when it did go my little four door could blow the doors off 5.0 mustangs and most older fbodys through the 1/8mi.
I've learned from my mistakes and that's why my Nova has a dual plane (Weiand) intake and a vacuum secondary carb (quadrajet). Ok, so there was a lot of engine building theory studying going on between then and now too.
Keep up the great work on this channel! You've been verifying I built the motor up in my Nova correctly. I'm looking forward to hearing this stroker motor run.
@@Myvintageiron7512 Yep, I was drag racing at 20 years old in my own car. I left home at 15, got myself a job at the local garage and never looked back. It was 40 years of automotive. I'm still mad at myself for not building a serious Nova.
This video and the one covering camshaft selection are priceless additions to my future engine build. I was given an LS1 from an '98 Camaro and want it to both make good TQ/HP numbers but also give me half decent mileage. I know you can't have both high peformance and high mileage, but there is a sweet spot one can achieve w/ careful planning. Its going to be a challenge w/ the lack of bore-ability of the block, but I should easily be able to hit the milestone of one HP per C.I. w/ a proper balance and assembly. My goals are maximum torque while maintaining emissions compliance, as its my daily driver.
I really like your videos; A++. They are packed full of information. I hate going to watch a video for information, and the guy takes up half the video watching him eat breakfast, and then going to visit his Uncle Bob.
thanks to reducing equations we can simplify (r*s)/6=4000 for the purpose of finding a target redline speed into 24000/s=rpm so simply divide 24000 by your stroke in inches to get the exact redline rpm.
Ariel Lezen I have 72.0mm stroke and I go to 7000 rpm can you calculate my engine redline
Exact stroke for max rpm of 7000 is 3.4285. What's cool is I just got my hands on an engine only made for 4 years 5 if you want to get technical. The stroke on this 383 is 3.380. So I have 0.048 to work with. Gets me thinking about the engineers and what they were really after. How about something that can be mass produced for intended use but, with a little modern (modern being used broadly, modern is just the time) technology for final touch up work. Can just sit happy right where a street RPM band engine should be for a V-8.
The issue is most production V8's are cammed/intaked to make power between 2-5k, after that they fall flat. If you change an engine to make peak power 5-8k customers would think its too sluggish or too much power pickup in the top range making it dangerous for inexperienced drivers. Its a tradeoff they had to choose reliability and fuel consumption rather then power
Ariel Lezen So since the tach is driven by the cam, every cam rotation the distributor tells the tach to double the amount of revoltions because the crank is 2x the speed of the cam ?
You just earned yourself a subscriber. Awesome video man. There is a lot of information in this video, but it's not spoken like it's being read from a book. It's broken down into "laymens" terms and it allows almost anyone to understand it. Awesome video.
Been around cars a long time and never heard of this formula before. Building a BBC and wondered about max RPM. Thanks for the info.
Very good video.....good explanations. I used a 350 Chevy for brackets back in the day with a built motor...good rods, crank, forged pistons, ported heads, bigger headers, good collectors with open exhaust, 5:56 gears, etc. Depending on track conditions I used Victor or aluminum Corvette/Edelbrock 180 degree intake..... If I recall I used a 30-30 Duntov with solids.....it was a good cam because I could open or close the clearance to vary how "big" the cam would be. I would run about 7000 rpm and go thru the eyes at 7200. It held together forever but I watched the tach like a hawk. The car was not licensed for the street. I guess I could have been more radical but this was before all the aluminum heads, etc came into being. I think in those days we understood more about how enginces, etc worked because we HAD to figure it out for ourselves with the machinist. Today, guys can open their wallets with little knowledge and end up with a pretty good engine.
When I was younger my dad built a 351W with Cleveland heads, and he swapped over to a solid cam, adjustable valvetrain setup with a lumpy cam. He always told me that a 351 could pull 7000, but I really wasn't sure how that was possible since the 4 cyl in our Focus barely did 7000. Now that I'm following suit and getting into cars, and that I have more knowledge, it's easy to see how to squeeze revs out of an engine. As always, well explained video.
+Ryan Eyster A 351W will turn 7000 it is feesable to go above the piston speeds I have laid out race engines do it all the time you just need stronger internal parts and a much better balance job 4000 FPM is a good safe max piston speed for a stock engine
The Cleveland will do 7000 more reliably because of the smaller crank journals. One of the other things that affects the rev potential of an engine is its ability to reliably supply oil to the journals, and larger journals require a better oiling system to supply enough volume due to the cast-off created by higher surface speeds.
You mean Windsor don't you? Cleveland is ordinary by design.
ThePaulv12, no, the Windsor is a wedge head engine, like the 302, that was never as popular for performance as the Cleveland. The Cleveland is a canted valve head, like the big block Chevs. It also has a shorter deck height and smaller main bearing diameter than a Windsor. A 2bbl Cleveland had heads that were more than adequate for most street and racing, but, the 4bbl heads had huge ports that are said to outflow a 427 rectangular port Chevy. These were the same heads used on the Boss 302 and had a very high rev capability due to the flow.
Good day I am looking forward to rebuilding my 4.0l Jeep motor this summer. Following the formula to figure out my RPM I should be able to build my motor to match the drive train. Thanks for the information and the simple way of explaining things.
what ?? are you afraid your engine reach 11.000» kekeke
try it first, then try to control it...
Thank you Tom Hanks
lol
HA!
bro, I wasn't ready for that comment 😂
Vicente Bianchini 😂😂😂😂
Vicente Bianchini where you going Jenny😂
Again thank you. Your totally right if your going to beef up the bottom end as to run high RPM it's wise to put money into valves, springs, Cam etc.
my 409 and 348 both topped out at 4300 RPM. 327-375hp slightly built about eight. But no matter what an engine was rated for I usually drove by ear and feel. Great video's, thanks.
I learned a lot just from this video, very well explained
You're missing the reason for the longer rod!! You understand the higher RPM and stroke reasoning, but the advantage of the longer rod is entirely geometric! A greater advantage is achieved with a longer and more angular focus on the crank increasing the leverage and advantage!
He didn't miss it. All he was talking about was the components and if they can take the speed you are wanting to spin the engine to. The advantage means dick if the internals can't take the forces and become separate pieces.
Here is an interesting fact you may not know. The piston moves faster closing in on and moving away from the top of the stroke versus closing in on and moving away from the bottom of the stroke. The reason why is because of rod angle effectively acting like it's growing the rod in length as it approaches TDC and in effect shortening in length as it draws away past TDC. The distance between crank throw and wrist pin varies with the angle of the rod.
Growing in length while approaching BDC, bottom dead center actually slows piston speed down. It may be hard to fathom but the net effect is that there is more dwell time at the bottom for cylinder filling and less dwell time at the top to take advantage of chamber pressure. Learned this phenomenon at the tender age of 70.
Hmm, with this formula, the Olds 350 and 403 appear to have a slight advantage over their Chevy cousins with the same cid. The 350 rocket is a highly under estimated engine. Early 350 rockets can be bored to the 4.125 bore the 425 and 455 share, but have a 3.385 stroke, They can also use the big block heads as a upgrade. Even with windowed mains, the 403 can produce some insane numbers.
I've seen dirt track racers consistently run 350 Chevy's with stock bottom ends to 7000 RPM but on a few drag race cars I've always played it safe to 6500. Had a 396 once that I would turn to 6000 RPM. But I'm a cautious guy. Great video and thanks for explaining the numbers.
I have a friend randy that built a Chevy small block back in the late 80s that saw the far side of 8700 rpms and that thing was a beast, it never came apart , it was in a 69 Camaro, I saw that car beat built 600 hp big blocks , one guy he raced and beat said i heard the horse power screaming out of your grill when you passed me
Until I had watched your video I had naively assumed that the connecting rod length was almost entirely a side load issue.
I had not realised that it also had an effect on dwell time..
you are right of course. It is a shame that people don't always pay proper attention, I cannot fault the information you provide.
I think that rather than disputing the facts people should perhaps watch the video a second time, well done on a well put together video.
4000/(stroke/6)=max RPM. Gives a definite safe answer that results in exactly 4000 FPM of the piston. Thanks for the info!
Equation works! My mercury v8 outboard has a stroke of 3.4in, so that means theoretical redline of 7000. Factiry redline is 6200, but the "race" version is 6500.
Great info that is data based. This equation takes the guess work out of what people assume is safe. Great articulation and explanation. Great job on the video. Thanks for taking time to offer this research.
Best explanation I've heard on the subject, great teacher.
Strong internals go a long way here. 4340 crank and fully forged pistons and rods @ 4.25 inch stroke hasn't cared about 7500 rpm in my little hotrod...Yet... Pettis performance builds 598 Chevy (race motors) with 4.5inch stroke that make peak power at 9k. Very informative video!
With this math my Olds 403 could rev to 7,000 rpm. Unfortunately the weak windowed block can handle that. Kinda wish I went for the full monte J&S Halo girdle (did install the 4 main girdle) I'll keep it to 5500 and less and hopefully I don't blow the thing to bits. The 403 bore stroke ratio theoretically is great for a high revving engine, but the block strength holds it back.
Terrific videos. Please keep up the good work. I learn every time I watch.
Thanks a lot, things are always more complicated then they appear. Keep these videos coming.
Would be cool if you did a video on the effect the connecting rod length to stroke ratio has on the hp and torque of an engine.
I've always wanted to build a Bug engine with a 1300 crank and the biggest bore pistons the bore centers would support and then have the cylinders long enough to support 2.3 x stroke ratio. Billet heads with the biggest valves that would fit without shrouding in the bores, and as close to a 14:1 compression ratio with closed chambers and D cup pistons. The camshaft would be tuned to the dwell time of the pistons at the top of the bore. The next thing would be a single plane pyramid intake with a tuned plenum and runners along with a Holley 660 center squirter carb.
I know the Euro guys like the weber carbs for throttle response, but a single plane intake with a combined tuned exhaust makes more power overall.... Anyway, would be fun to build such an engine.
and then your valves melt because tetraethyl lead 3 is bad for the environment unless you use 109 octane leaded av-gas.
+Ray Main You're even getting me excited. Remember high compression = pumping loss. There have actually been a number of very high compression production engines over the years and after the first run they were always backed down to around a still high 11:1.
Another thing, by my way of thinking, very high compression is only worthwhile (on the street) if the ignition timing is
That is why I love the 302 Engines because they are Short Stroke Wide Bore and you can wrap them out even stock I nailed 5500RPM in my Bronco few times and it felt smooth at that high RPM Also Short Stroke wider bore engine have much better Throttle response in my Opinion.
Thank you for this video. I've been wondering about all of this for years.
R.P.M's, i knows MANY mechanics/technicians use plural on minute. I have 2-96 Roadmasters with the LT1 cast iron head, I have no idea of the casting numbers but 2000 R.P.M's with the rowing package gets me 80 MPH all day. I bought one of those tuners to tweak dis n dat and raised the governor from 108 to lotz more and put higher speed rated tires on one of them and now I've been to 3500 R.P.M'$ which is/was north of 130 M.P.H'$ on highway 99. Built a few engines and enjoyed the few videos of yours I've watched.
Gene from the left coast near the state Crapitol
Not to mention, bearing surface speed with longer stroke requiring a better oil delivery to cool the bearing surface. With oil temperature being more critical to making power, the window narrows significantly. The old rule of 10 psi per 1000 RPM may not be sufficient.
It's really a function of thermodynamics and friction...with the mechanical design being adapted to address the dynamic metallurgical structural weaknesses (a multi degreed Aerospace Engineer who works for a large American defense contractor.
Thanks, this was a great explanation on how to find an engines recommended redline and performance capabilities. As a side note what is the stroke length of a 5.3L LS engine or would a 4.8L LS engine possibly be a better option? I would like to use a M122 GT500 Roots style supercharger and possibly even use a turbocharger as well.
Now that was informative thanx bud.
Ive got a 355
Id say a lil bit more than moderately built .i twisted it to 7500 and 3 of my harland sharps started clacking pulled covers off and had 3 backed off to abot .050 .supposed to be .021 wp heads,1.555 springs,doubles with dampers. Cam .600 in
.625ex..rockers actuall hit stud girdles.ALMOST A CATASTROPHIC.
Great video, I have a 2003 Toyota Matrix XRS which has a 2ZZ-GE engine that red-lines at 8200 RPM with a stroke of 3.35". By your formula my pistons are traveling at ~4575 FPM. But I guess that is what you do when you are a large corporation and reuse and engine that you put in a Lotus Elise/Exige.
Forged steel crankshaft. Refined rods and pistons. Much better castings than the engine community he is referring to.
Type of alloy used also plays a part.as we all know hypoutechtic pistons love to handgrenade if pushed over max speed
I just calculated a few for comparison:
1) bmw 330ci: 3173.3 ft/min
2) Honda S200: 4960.6 ft/min
3) Yamaha R6: 4870.8 ft/min
4) 2010 Formula 1 4724.4 ft/min
*I think some factors that play into RPM are:
- reciprocating mass
- secondary and primary balance
- airflow at high RPM
- stroke vs bore
Oh for sure the weight of the rotating assembly is key we like to use 4000 max for stock engines it's really safe but certainly not something that can't be surpassed
Thank you for your Chevy 350 Video Series. These videos have helped me improving my technical understanding of the 350.
Im saving up for my first engine Rebuild or Engine Build right now.
....Best Case scenario....
I'd LIKE to see 600 hp/ 550 Torque out of my current 350. either in the 383ci or 400 ci. but since I still need to iron out other details on the truck. I'm probably just going to do a HO 350 rebuild for now. so I can drive it while I get the other details fixed as I go.
I'm considering buying a built crate Engine or sourcing a LS Engine later.
the problem I have with the LS Option is.
all the little stuff im going to need in order to make the LS work in my 94 S10.
Wiring. Engine Mounts. power train. Computers. transmission linkage. cooling systems.
yada Yada yada.
I have a 92 S10 myself. As well as a 1970 350/300 4bolt along with a good 350TH to use if I wanted. Same problem as you. The LS option is for sure going to require extensive wiring and what the heck, the speed it is going to generate might as well figure in a suspension as well. Lord knows the flimsy shocks that you get for the S10's isn't going to handle the corner speeds... I'd like to do anything/everything to the 350 and sit it in it, but hate to think that it will be just a putt putt truck...
@LORDdeath Gaming You're making more out it than necessary for an LS swap. The wiring is a simple affair that you just lay on top of the engine, once installed, and start making connnections - it falls together like falling dominoes. I was intimidated by the prospect as well, but it went quite smoothly, once I hunckered down and started the process. As for your plans for your SBC, just remember speed costs money, so get rready to spend a pretty penny for an engine w/ those specs. Just sayin' those are big block numbers. Best of luck.
Here are some basics: factory built engines are usually only harmonically balanced to about 5000 rpms. The first thing I do with an engine build is called "balancing and blueprinting", where the crankshaft is harmonically balanced by the machine shop to 10,000 rpm without vibration. Then we "blueprint", this involves weighing all of the piston/rod sets, and we find the lightest one. They never weigh exactly the same, and that's what we want: we grind a bit off each one until they all weigh exactly the same as the lightest one. Now you have a bottom end that can take huge revs without shaking itself to death. The limiting factor, now, is the strength of the valve springs, and their ability to close the valves fast enough. My old Suzuki GS1000 floats the valves with the stock springs at 12,500 rpms. "Floating" is when the springs can't close the valves fast enough, and they sort of just float open. All of a sudden the engine will just crash, and loose all power at a certain rpm. If I put heavy duty springs in, I could get around 14,000 before they float.
Your butt is sucking pond water on your basics. How is the crankshaft balanced to 10,000 rpm when the balancing machine only spins the shaft at 500 rpm?
And how did they balance the crankshaft without first equalizing the weight of the pistons and rods to make bob weights--unless you're talking about a 4 cyl or straight 6.
I got a small block Chevy 327 , it has 12:1 forged pistons , steel Vette crank in a 4 bolt main block ,
It cranks 11,000rpm before the valves start to float
I was just watching you talk about this subject in your new How To Pick A Cam video and it seems like it would make more sense to pick a piston speed and calculate for RPM. With a desired piston speed of 4000 and a stroke of 3.5 inches it would look like this 4000 X 6 = 24,000 ÷ 3.5 = 6,857 Then you just round down to the nearest hundred just for safety, 6800 is the right RPM. If I'm wrong let me know.
That is exactly correct!
Great job explaining this...i see things much clearer,,thanks
Glad it was helpful!
Exactly what I was looking for, just a curious engineer
glad it helped
Cool information my stroke is 3.6 so it seems as 6500 is the max safest rpm I can go on my engine which is 3900 fpm. And you said the longer stroke gives more torque which is interesting as I could tell my engine was a lot more torquey than my 3800 L36 powered car which according to this formula the L36 can easily do 7000 rpm and would probably max around 7200 rpm which gives me 4080 fpm on that engine.
This video made me subscribe thanks for the info.
I am spinning a 4.6" stroke at 7400 RPM.
But as he says, much must be done to be strong enough to do it. Billet crank, rods and main caps to start. This is in a one off tall-deck LS race block. (LS blocks have fully girdled main caps unlike SBC, so that helps too)
But that give you an idea of where things can be taken if you want it bad enough.
and 7.000 is a lot??? kekek you should have seen 11.000 rpm
Excellent video. Makes this pretty understandable for us dummies.
I really love your videos man. Keep it up!!
What does it mean when a connecting rod flies out of the bottom of the oil pan? Really curious if its going to affect my fuel economy.
351cleavland usually the failure of the end cap or connecting rod bolts ... i.e. ..flies out .. other sources of failures can contribute too .. lack of oil psi to the bearings , cause the bearing to fail .. excessive clearance leads to the "knocking " then excessive heat , gaulling , seizure , boom ... the rod is the last to get oil ..
put the rod back in and jb weld it back in place, should be fine just use plenty of JB
...change your oil more
randysengine service Sure, I did that and a week later a piston flies out the engine compartment into the cabin and up and out through the sunroof! I am 50% sure its not going to bre covered by warranty!
Your fuel economy will improve because the car becomes lighter due to less rotating mass in the engine ;)
He uses a 6 so it's easier to calculate piston speed. There's two stokes in one rotation of the crank so the stroke needs to be multiplied by 2. Then to get feet per minutes you need to divided 12. So essentially your dividing by 6.
Stroke x 2 x rpm / 12 = fpm
Very informative especially for someone who is not a mechanic, but I have a question- If I have a neo vvl St 20 will installing a vvl controller and setting it before 5000 rpm harm the engine? Thanks
i've just seen the video
and after doing the math the results are!!
my car chrysler SRT8 HEMI 6.1L
after few upgrade
now it has 4.250 strok
4.125 bore
CNC heads etc....
also it is my daily use car
and with 3.73 diff the RPM is always high
and 6500 RPM is a number that i reach as my daily routine
if you do the math:
5650 rpm × 4.250 ÷ 6 = 4002 FPM
what about 6500 rpm
its more than 4600 FPM
dyno test is: 510+ rwhp on gas pump
I had a roommate in the early 90s, with a mildly hot rodded 350 in a '64 Chevy II. He had a very safe and logical method of determining red line, which required no pesky mathematics. He simply kept revving the engine til shortly after it stopped making noticeable power anymore. On a 100% completely unrelated note, it spun a bearing 2 months later......
HighlanderNorth1 yea because the cam has a big factor on when engine quits making power not red line lol
Due to rod geometry, the fastest piston speed is usually in the top 1/3 of the cylinder. In the center of the cylinder, the piston is starting to decelerate as the crank comes the 90 degree point, actually starts decelerating at about 60 to 80 degrees, and decelerates the most as the journal starts to swing back in the bottom half of the stroke, stopping again at BDC. Also, a short rod engines like the Ford 302W or Chev 400 small block have faster acceleration away from TDC, once again due to rod geometry, than a longer rod engine, like the Ford Boss 302 or Chev 350, which can cause a piston to pull apart easier at the same RPM.
That depends on rod/stroke ratio
Most engines peak out at dead middle of the stroke
Engine with short rods and long stroke will have 2 peak pistons speeds near 1/3 down and 2/3, but actually slow down some in the middle of the stroke. that's because rod angularity accelerates the piston against the cylinder wall, but this increases runner air velocity and can be used to increase volumetric efficiency
Peak piston speed at redline for a 5.0L is 82.5, while LS3 is around 72mph
The rod/stroke ratio will dictate piston accelerations and decelerations, but geometry dictates speeds in any part of the cylinder. Short rod will have quicker acceleration/deceleration, but, as the crankpin nears the halfway (90 degree) of stroke, piston speed starts to decrease as the rod angle change slows, no matter what rod length, usually around roughly the 30 - 45 degree range of stroke which has the piston in the top 1/3 of the cylinder. A shorter rod may have the piston farther down the cylinder, but not usually at 1/2.
The difference between short rod, such as a 302 Windsor and longer rod, like a Boss 302, also dictates the cam requirements of an engine. Shorter rod engines like fast valve opening and higher lift at TDC to make use of the quicker piston acceleration away from TDC. Also makes use of larger carbs, valves and ports to allow less restriction to airflow acceleration as the piston moves from TDC.
An easy way to study rod length on piston movement is to make a 2-d cardboard replica of a crank and cylinder. Make a circle to show the crankpin rotation and use a ruler for the rod. Pick points around the crank stroke and then match the ruler to the centre of the cylinder at different lengths from the same point in the stroke. You will see how the piston is higher or lower in the cylinder as rod length changes. The fun thing with this is that you can use rod to stroke ratios that would be impossible in real life to exaggerate the results and get a very good indication of how they affect each other.
Been a auto Tech for over 60 years graduated in 1968 from Lincoln Tech Back in 1970 bill Jenkins brought his Vega to the nationals a 400 Small block with A327 Crank Which worked out 332 cubic in Big bore short Stroke makes a killer motor They laughed at him at the end of the meet he put all the hemi's on a trailer
@myvintageiron7512 You do a great job explaining how things work! Your videos are the best. I wish Google would link to more of your info in the search results.
Question: To what degree does the width/resistance of piston rings and the weight of the pistons (in after market situations) play a role?
What is the “6” referencing?
Great video. Thanks for taking the time.
just an educated guess but the reason why you use 6 instead of 12 to go from inches to feet per minute is because the piston travels the length of the stroke twice for every revolution . so really what you are doing is ( stroke/12 ) x 2 which is the same thing as dividing it by 6
Great info on RPM. Thanks for putting these videos together.
Great video. You explained the concepts perfectly.
Great explaination. Just hope you can tackle cam design for the other unemformed some time, especially the part on advertised duration (SAE measures @ .004, where Crane Cams measures their cams), Comp Cams ( at .006s), and others and how this affects actual cam duration and how this affects power.
Could you add what would help turn more rpm I build alot of dirt track engines in many classes alot of people need to understand what helps engines live at rpm , great video thank you .
Building my Harley Engine for the 3ed time , I set my Over Rev limit to 5500 RPM now your video has me thinking I could go to 6500 , Each time its been my fault it has blown, Bad lifters, bad cam bearing, then a bad pushrod .
Just doing the math. A modern pro stock engine's piston speed is roughly 6,400 fpm. (3.500 stroke and roughly 11,000 rpm) Food for thought.
Sounds about right race engines see over 6000 FPM on a regular basis
old man bell built me an engine that is nuts after he built it he told me this engine will do 10,000 rpms all day long so we had to test it we took it up to 15,000 rpms many times racing it and we run pump gas only running 13 to 1 compression with no problems no pinging or any thing it just ran hard just one problem with it like to rev real fast with water pump alt and power steering could not keep up and it will twist the front part of the crank right off but the class we were racing requires to be street legal has to have all the stuff to drive on the road and no stripping the car down so i had to learn not to rev it to hard but we never lost a race in my area but far from being cheap to build bell said he did everything he could on a sb even season the engine for a year and polished the inside of the block started with 202 angle plug heads but bell did his magic to them too , stock headers will not fit no more how he described the engine was a indy bottom end with a dragster top end he said this way u can run real low gears and not lose top speed and u can gain torque thew the gears . i really could not believe this engine even when i was racing it the rpms was insane the sound that it made would make any man cringe just screaming sound i have a lot a race engines but this one is special next i am building a bb chevy because i just got a set of hemi heads for bb chevy of a funny car for 300 bucks
i see that you are doing it for dale with that hat, he told me he was proud.
Sort of off subject but could you explain briefly the designation of Chevy engines. I see references to LT1, LS, Gen1, Gen2. Pretty confusi g when looking for parts.
Gt350 voodoo engine. 3.7'' stroke. 8250rpm, 5087 feet per minute. Crazy!
98 spec JDM ITR Type R engine 3.433" stroke 8,900rpm 5092 FPM. Or at least that's what the rpm gauge reads when bouncing off the rev limiter.
Your tutorials are very informative....
Glad you like them!
Thanks. I enjoy watching your videos!
Stroke the connecting rod length equals piston speed for when that piston goes up to top dead center and back down length of the connected rod
Jeff. 1 complete cycle or 4 motions is 2 rpm because that is 720 degrees of crank rotation. 1 360 crank rotation is 1 rpm. So 2 strokes is 1 rpm
Reliability/durability of the crank and bearings are what limits rpm, right? They the failing components of high rpms, right? Can you increase rpm and/or add stability/reliability to the exicting redline by using a higher viscosity oil or some kind of racing oil?
Great video. Not sure where the 4000 fpm number comes from, but definitely gave me something to consider.
I used your equation in reverse to determine the theoretical redline on my Buick 455:
((4000 fpm) x (6 factor)) / (engine stroke) = (theoretical redline)
(4000x6)/3.9=6,150 rpm. 👍
yeah I wouldn't run a 455 to 6,150 for very long though, the oil system just won't doesn't support prolonged revs. The Buick, Olds and Caddy engines suffer from pumping oil to the top end and not draining back to the pan resulting in bearings not receiving adequate oil. This can all be "fixed" but be careful in a stock application.
What I was hoping would be covered in this video was the effect of longer rods on the same stroke...I've seen a lot of guys build "long rod" engines, but are the gains worth the time and effort? I've also read that long rod motors make much better use of small valves and ports, but I haven't come across very many A-to-B comparisons.
Between 70 to 80 crank degrees on primary stroke which is tdc to bdc that's its fastest speed.and between 2 to 15 degrees past tdc is highest pressure in chamber.
There are so many parts available for the SBC that its bery hard to figure out the correct combo.
Can you do a video for a 600 HP Chevy 350 build?
Plus can you explain how to tell if the block is high tin/ nickel.
I have a 350 4 bolt main, bored to .060 over with a .120 cylinder walls, behind the timing gear is has 10 and 20 molded into block. Someone told me that means it is a high tin and high nickel block. Is this correct?
P.S. I will be using AFR 220 (2.08/ 1.6) heads. I will be driving it on the street, but I want it to sound like a Pro Mod when it idles.
Thanks for your help and love your vids.
So basically if you have a bigger foot on the accelerator, the engine can rev harder?
great video, came at a really good time, I am putting my 283 short block together soon. really want it for a RPM grabber for no good reason at all, just to have fun with... I am deciding on heads, I have flat top forged pistons, stock rods with ARP bolts in them. Q: stock heads fully ported( non humps) or newer style "vortec" head (305ci) or something else. any advice would be awesome, thanks!
I have video of the 283 with vortec 350 heads and I loved it but they ended up being cracked and that is why I am redoing it. just looking professional advice as I am about 35 years old and this is the first 283 I have messed with. thanks
Great explanation lean so much from your video. Thanks! I like the math, is there a math way to see what rpm an engine should turn?
I didn't learn this in feet / min, I come from a metric country (Australia), and we do this in m/s. But over time the maximum recommended piston speed has gone up from about 12 m/s when I was a kid, to about 16 m/s now. It's also worth going over rod length to stoke ratio. I would also mention that engineers at the factory do their calculations, but then they do a practical test. They run the engine on a dyno at about the maximum power for a time (hours, not seconds) and then strip and inspect. When I was a kid, in the '70s, Honda was supposed to run any production engine at redline for a week. If the engine suffered serious wear or damage in that time, the engine spec was changed or the redline was lowered.
+Kneedragon1962 Also maybe mention, there should be a natural safety margin between max power rpm and redline. One real criticism of racing engines is the ones that are still gaining power (or sometimes even torque) at redline. They're difficult things to use safely, for a number of reasons. Instinct and the seat of the pants will tell you to keep it pinned because everything is going great...
+Kneedragon1962 Engine go's💩💩💩
Kneedragon...Used to be a saying 'They run the strongest just before they blow.
Find a measurement converter on line, and convert.
Well said. One thing though: I would imagine the ceiling of 4k fps could be raised with low weight reciprocating components.
Well yeah. Nascar was turning the 358 ci. Fords and Chevy's 6800+ way back in the early 80's. True they didn't have the parts we have today, but they were doing a lot with cast iron cranks and stock rockers... And yes, they did blow a many engines as well...
hi great vid , does this same rule apply to the 366 gm big block truck engine ? or are all stock engines built to a certain standard or envelope that all stock engine engineering fall into ? .the reason i ask is because the 366 has extra heavy 4 ring pistons and planing to build one for towing , redline under 5500 rpm , Thanks
I like your videos! been pushing your numbers around according to these numbers I could push my 6.6l duramax with a 3.9 stroke to 6150rpm! I wouldn't do that I'm sure somthing would let loose way before this! perhaps the 4000ft dosnt apply to diesel applications?
Good video but, connecting rod length does not affect piston speed or piston dwell.
It does however greatly affect sidewall loading and force on the crank. Particularly during the combustion stroke, where most connecting rod failures occur. The longer rod reduces both sidewall and crank fatigue but increases rotating weight and to avoid over-compression, the wrist pin location in the piston must be moved up creating longer skirts which weakens the piston itself.
you are partly right and partly wrong rod length does not change average piston speed that is true however rod length does change when and how the piston speeds up and slows down also rod length most definitely does effect dwell time anyone who has degreed a cam with different rod lengths know this
@@Myvintageiron7512
I wasn't trying to be argumentative or condescending however, you are wrong. A shorter rod increases the angular reference to the piston wall which causes the piston to accelerate and decelerate faster as the rod reaches parallel TDC and BDC. As you said, the average speed does not change, acceleration just moves further from center of the stroke and closer to TDC and BDC. At TDC, the rod is perfectly parallel to the chamber. The piston stops moving roughly 1 degree from top center so you have right at 2 degrees of little to no movement. The distance from the crank to the wrist pin does not change dwell time however the circle of rotation (I.E. the stroke) does. A larger circle takes more distance to travel 2 degrees and therefore more dwell time.
Now for your last statement.... Anyone who has degreed a cam regardless of rod length knows to set their piston stop a few degrees short of TDC to find perfect center and isn't worried about so called dwell.
yes I agree you don't really worry about dwell when degreeing what I was getting at is you can see the difference in dwell time with a dial indicator on the piston and a degree wheel on the crankshaft use the same cam and check the crankshaft movement with a 5.7 rod and then check it with a 6"rod the crank will move more degrees with no piston movement with the 6" rod than it does with the 5.7 rod IE more dwell time
I don't understand why the piston travels faster if it has a longer stroke. To me it appears, according to your formula, that the speed(rpm) is remaining constant but the distance covered is increasing with stroke. The stroker is not traveling faster but moving further therefore momentum plays a bigger role. What am I missing?
I was getting 7 grand shifts out of my 68 327 Camaro until the drive shaft came through the floor board. And that was with points not electronic ign. A 4speed trans and 3:08 rear.
I believe the piston is traveling fastest when the crank journal is at a 90° angle to the the cylinder bore. As it approaches the top and the bottom of the bore it slows down as it stops. The cranks rotary motion is at a controlled speed. Controlled by the reciprocating mass and the mass of flywheel and other engines components so it cant just takeoff freely on the power stroke. Its being governed so to speak by the compression strokes of other cylinders ect. The problem in keeping an engine together is the quality of the parts when the piston changes direction at the top and bottom of the stroke. The crank at the top of the stroke as it changes direction "yanks" on the rod and piston pin. Poor quality parts or a part with an defect or too much mass can be damaged.
The inertia of the rod accelerating in the each direction can cause the rod bolts to try and stretch as well as the beam portion of the rod. Moral of the story for lower end reliability use as long of a rod and light a piston combination as you can get away with while using ARP rod bolts. Another factor is minor and major cylinder wall loading this can be critical in Ford engines like the FE and Cleveland series which are both known for very thin cylinder walls.
I agree 100% your right on with both points
I race 340 Mopars as there 331 stroke and 4.04 bore makes a 6,500-7,000 quite safe with the proper bearings and pump.
learn something new every day. Love it!