I believe the correct term for this is "realized power". If you keep increasing the cylinder-head flow capability (cfm) and you keep getting measurable increases in power, then you are seeing "realized power" gains. If the last increased cylinder-head flow increase does not add to the power output, then you have reached the maximized power output (from the cylinder-head's contribution) for that particular engine configuration. ALL cylinder-heads are a restriction to an engine's Intake airflow requirements for true 100% cylinder-filling. We can know this by looking at the fact that the only way to theoretically completely flow at the rate of the piston's descent, would be to take the cylinder-head off of the block-deck completely during the intake stroke, then immediately replace it at Bottom-Dead-Center before the piston rises again. Even if the cylinder-head was only equipped with a single valve located dead-center over the piston, as an intake valve, it could not flow the full volume needed. With that as the baseline for maximum cylinder-filling (and therefore maximum potential power output) we can see that there are many limitations to maximum power between the cylinder bore and the throttle-body (which should be the only, and variable, "chokepoint"/or throttle) in the entire induction system. I believe that all naturally aspirated engines (and most supercharged ones as well) are airflow-limited to what amounts to a smaller displacement engine, in realized power. One clue to this is that we never seem to achieve maximum potential output from any given engine size. Most builders go with bigger engine size or displacement to get the desired or needed power increase. The best way to maximize any particular engine's output is to use experience (our own or from someone reputable) to get you close, then "cut & try" to get the true best output from it. This is tedious and time-consuming and of course expensive to do. That is why most of us will have to settle for some power output level somewhat better than average, without ever realizing the absolute maximum that could be achieved with that engine configuration. That is what makes this profession or hobby fun. Learning and enjoying the fruit of our experience while trying to achieve the best possible performance. If someone were to figure out the absolute best combination for every possible bore/stroke combination, it would ruin the sport for the rest of us I believe. If you are one that has figured it all out, I know I probably won't have to ask you to "keep it to yourself"!
The voice over is great for this kind of discussion because it makes it easier to focus on what you’re explaining. For other topics, it helps to have you show and say simultaneously. More specifically, when you tell stories or talk about PRI or shop tours, we want to hear and see your body language. You were clearly more even toned in the voice over, but your personality and enthusiasm show up more when you are physically on camera.
Interesting info Eric! You just answered a few long standing questions I've had. I recall asking about stuff relating to this in a previous comment. If I wasn't 60 and on a limited income, I'd be personally traveling to your shop with heads in hand! Wish we had easy access to guys like you with your knowledge and skills back when I was in the middle of all this. Keep the quality info flowing! (pun intended) The more, the better.....lol
Great vid. I think many people don't understand the acoustic resonance in the intake, and the port as a wave, that starts, and stops moving, speeding up, and slowing down, and how size, shape, taper and radius of the intake runner all compound the complexities of them. Making a powerful naturally aspirated engine is harder than bolting on boost.
Hi Eric. Thanks for the video. This is something I'm looking at now for a 383 I'm designing for my son. You confirmed the numbers I came up with. It's been 30+ years since I've done this so it's a big memory and learning curve. Thanks for the help. Now about the talk-over format. Personally, it doesn't work for me. I'm pretty sure I stick with the videos to the end or close to it. I'm just a majority of one so if the others like it I'll keep watching. Keep up the good work.
About voiceover: the audio is higher volume and more consistent,,, altho there is a super minor hiss noise,,, like software compression hiss. Go to 1:17 amd listen closely,,, but both are good,,, voiceover usually more concise and organized format for us sometimes audio only subscribers
You are missing a key consideration. Time. Ultimately Torque is a function of Time X CFM. The time is in the camshaft. You can make the same power with a smaller cam and head that can flow better. Camshaft timing has its limits, such as drivability, emissions and operating RPM. There is also a modulus, for port size and runner length, a smaller port will have less volume or weight that needs to be re-accelerated when the valve starts to open so it will respond better to transients and lower speed operation. So you have to pick a cam (time) and work backwards. The smallest port with the most flow will offer the best transients. Dyno doesn't value transients which is why many dyno hero motors do nothing on a road track where the driver needs throttle response to transfer load and steer the the car.
You hit the nail VERY HARD ON THE HEAD....... I always say : a dyno revving up 500rpm/sec ........... That takes 4 seconds from 6000 to 8000 rpm..... Thats too slow. Nobody uses calenders measuring accelaration....
Circle track guys had this figured out decades ago, people read magazine articles and get caught up in big CFM, big peak Dyno hp numbers, put it together and wish they had left it stock, there's a good reason for the compression and gearing/stall recommendations given for shelf cams the bottom of the page guys usually spend a lot of money to make the car go slower. I'd venture a guess and say that 90% of the street car crowd would be happier with more cubic inches, even if it shows less peak hp will run, drive, and accelerate from idle to 4000 great.
If you think that the best racers out there, regardless, what kind of racing road race drag race whatever if you think that the most successful people do not use a dyno Engine or chassis you are wrong by a mile they’ve been using them for decades and decades, I know you don’t seem to like them or respect them for some reason but you’re just plain wrong
Are you trying to say overlap determines the rpm where peak efficiency occurs for a given combo? In my mind, cfm is the second concern behind velocity, yet both are critical for best output..
I do agree somewhat. I left the cam part out because it really could make a series of videos not something to just throw in this one. The smallest port that flow the most I have addressed in previous video. It’s really in what rpm range you want to accelerate that determines port size. Thanks for the comment.
When the carburetors larger on a motor like that if you are after straight power and not drivability, you go as big as you can wear it functions properly. It does come down to again pumping losses, as you stated like the ports. Due to the design of a carburetor it will always have some type of pumping losses due to the Venturi design. They actually tested this theory an engine power and showed the engine had less vacuum at high rpm so I can only attribute this to pumping losses. We are talking very small amounts, however.
I like your vids, I think stuff like this tends to be lacking sometimes in Engine Building (Hot Rod mags/marketing). I'm new to all of this, and learning. In reading Smokey Yunicks book, he talked about the whole system being a Venturi into a Venturi into a Venturi to keep velocity up. Interesting theory. I'm learning in a wierd but Interesting way, lol. Building TQ in a Jeep 258 (Dyno'ing 3 heads, stock, 7120 4.0 and the Edelbrock 50169). For me and Jeeps, over carb'ing and too much flow has been an issue. As us normal Jeep guy's are only working within 800-3,500 RPM. A cam is next, but sticking with my little Weber 38- custom Aux Vent's and I ground downed the Emulsion tube.
I have noticed on our asphalt circle track car that is a 358 big boar small stroke 12.5 compression engine when we rum Winchester speedway if I put a carburetor that flows 965 cfm we will pick up 4 tenths over our regular 850 cfm carburetor Thank you for the video
Sorry Eric I've missed a few videos. I've argued oversized throttle bodies for 20 years. LOL!!! Good stuff Eric. Separates us educated from the forum kings.
I dont know a lot about cylinder heads , what I have learned is from my limited experience. I built a small block chev a 302 a long time ago for my 68Camaro a four speed manual. I bought a set of heads that came off a g gas car that sent a Monza to I think 9.98 at one time . I built the engine in I think 1980 so the heads came off a car before then . At any rate I built a engine capable of turning 7800 or so and stay together. It ran hard all the way to the Rev limiter. It would have made power past that if I had the bottom end to go there . For me on a hot rod I want the engine to pull hard and not lay over . Heads is one area I try to get the best I can to do what I want . So I just ask the porter what do I need to make this much power . Lastly I rather have a really good set of heads and a little less cam to accomplish the same results. Thanks for your good advice
Great topic. How'd this work on the stock heads in my 1988 4.3 powered S10? ....maybe add some Manley race flow valves and change the exhaust to 1.6 before porting. What, 50hp? 😁 Very enlightening video 👍
All about knowing that rpm you want it to work at sometimes the mild head with the right cam goes really well . But at a pro race build we know that larger port and cfm will make what rpm we want , with the cam it needs , every single build needs its heads to suit, simple
Hey, sorry to comment again, lol. Do you have any vids on building TQ? I'm VERY interested in how to keep a high velocity flow on smaller ports, such as just port matching the roof of ports/matching intake with top of port and no grinding? I am working with an inline 6. Would this help the intake to keep the Velocity up, especially with a carb for low RPM TQ. And do you have vids on intake mods? I've rounded out the bottom of the intake where the Carb sits, to allow more flow, not sure it made a difference, lol. Like an inverse Velocity stack, sort of, which I know stacks work, as I've seen it testing with Smoke- tried to increase CFM on a Weber 38, it was a fail, lol.
The bigger the cylinder diameter, the more area on overlap for the scavange to fill, the more cross section you need, stroke just adds VE after the scavange.
im more thinking like .. if i port a top. i need to do something about the entire exhaust system also.. also the intake system. And a new engine... better springs. and a more aggresive cam to gain something.
I'm stuggling with this right now myself... doing a small block mopar just for beating on the street and having fun... not a lot of head choices and i really want TFS heads but they are overkill by a mile, the choices below that are not much cheaper but not near as good either.. for something that will rarely see over 6k rpm, not sure where i should throw money at this point..
@WeingartnerRacing can you do a video showing flowrates against depression on an orifice just to see that relationship? Several people will automatically go “yeah but a Holley is measured at 1.5” and that’s a restriction”
Head flow in the auto community is like power ratings in the audio world. How many watts? It's easy to measure I suppose so you gotta have a number to throw out there.
Too many are too concerned with them almighty flow numbers! There's also port velocity that you might want to be more concerned with, in my opinion anyways. I'm no professional head porter by no means whatsoever but I've read a lot of books on the subject from people such as David Vizard and such. Maybe explain that to people!? Great videos guy!
@@WeingartnerRacing thank you for these videos so much good information on heads not everyone generally uses. I have a set of these 230cc cnc Trick Flows and basically took them out of the box and bolted them to a 406ci. It made decent power with a unported super victor and a street roller cam.
We often forget that carburetors, Holley 4 barrel style at least originally got their cfm rating @ 1.5”hg. That’s 20.4” water. Making best power we want to reduce vacuum to a minimum at WOT to allow greatest air/fuel density to increase power. If a larger carb such as Eric’s 1000cfm drops WOT vacuum to .7”hg then what would that carb flow @ .7”hg or 9.5” water? Surely a less cfm figure but we are hung up on the flow number @ 1.5”hg. Most carb experts don’t talk cfm but rather dimensions of venturi, throttle bore and venturi to throttle bore ratios. It’s phenomenally difficult to get people to understand engines operate off density and not cfm. A carburetor is a density regulating device, not cfm changing device.
AFR told me no.I talked to Adam at AFR when building my 406.We talked about the 195’s and the 210’s.With the cam I am running and gear ratio and what I plan to do with it,Adam had said I was borderline.Mention one of the issues,,if I ran the 210’s I might zing the RPM’s A little to quick.So I was borderline.
Where can a calculator be found for determining head flow needed? I'm building a ~13:1 LS 402 and have LS3 head, but can more easily keep the compression up if flow from say a ported 243 is enough.
We see cfm numbers for intake or exhaust flow and infer results, but the actual flow characteristics are dynamic, not static. Further, exhaust flow can have a huge impact on intake flow (remember the 5-cycle cam from Isky?). Flow through the carb or throttle body is mostly the average of what’s going on in the cylinder head. So steady state flow from a flow bench gives you a piece of data, but it’s not the total answer! The dyno, on the other hand, gives you the actual result! Can’t wait to see some comparisons with The Mule! Let’s do some math. At 6000 rpm an engine has 50 intake cycles for each cylinder every second, or one every 20 milliseconds. The intake valve might be open for 250° out of 720°, so that is roughly 7 ms. The 400 cu in engine has eight 50 cu in cylinders, so in the 108% VE engine we have 7 ms to move 0.029 cu ft of air. That equates to an average flow of roughly 250 cfm, but flow doesn’t turn on and shut off in a square wave. If it moved as a sine wave, the average could be around 0.636 of the peak, or 390 cfm. We use clues like the flow bench to help determine the best way to make power, but the numbers only reflect a part of whole. The running engine tells the final story. Thanks for this video, Eric, it’s a good one!
@@stevenbelue5496 the original g1 with canted valves was not a good design, they tried to design it to work with special rockers, they had problems, had trouble with the guides. There is a reason they stopped making and selling them. Haven't heard much about the g2 twisted wedge sbc heads
@@stevenbelue5496 Well like anything else, if you pay close attention to your valve train Geometry, I think they can be made to work fine. And with some minor port work I am sure they will make great power.
I think , the factory LS3 head flows enough to support any fast street type car, any more work done then that is wasted unles you want all out race car. its already been shown to support over 700 hp untouched.
My 2 cents. Peak cylinder head flow is demanded by the pistion, and when does said piston reach its peak speed? Around 70-75 degrees crank duration. Or, probably around when the cam is in the 0.4in range. As you have seen and tested, improvements in airflow here are attributed to improvements in output. Next information drop, Pipemax has a function of calcuating cfm from piston speed. It brings up a large spreadsheet showing, piston speed, crank angle, rod angle, and cfm demanded by the piston. Waaay back in 2006, I ran a simulation using Pipemax on a 1600cc engine. It stated that for a 400cc cylinder, its piston cfm demand was 275cfm@8250rpm. If that was doubled to an 800cc cylinder (for a 6.4L V8), I would guess cfm demand would also double to 550cfm@8250rpm. We also have to understand that a flowbench operates at 28in of H²O, where a piston can generate far greater depressions than this. This stretching air is an invisible friction torque loss, and one way to lower it is by adding more cfm to the cylinder head. In a nutshell, this is where a pumping loss can be easily fixed because adding a better flowing head reduces the "strecth on the air." It's also why a cam change is needed, as the strech into the port is less, meaning less velocity. So, an earlier intake closing point is needed (big head small cam V small head big cam debate) Its also the theory on why Ford made the 4V Cleveland head. Small cam, big head. As a side note, the moment manifold vacuum hits 1.5in of Hg, there is effectively 13.7psi entering the cylinders. 1psi loss = 7.5% less air mass. The volume is the same, but it has less weight. Installing a bigger carburetor helps bring back that loss. There are other factors that then come into play, like running a finer grain booster because less vacuum means the fuel is harder to vaporize and stay atomized. This may theoretically be why a 1000cfm carby returns improvements over the 830ish one you said.
Pressure differential is what makes air move, yes peak piston speed will create the highest pressure differential but as long as that pressure differential is kept below 3.77psi then you won’t be stretching any air causing it to reduce its density. The pressure differential determines what the average airspeed is within the port and as long as your under 3.77psi pressure differential then the minimum cross sectional area won’t go into choke. Pipemax gives you a number at 28” test pressure as a reference to go against, this reference is calculated across what average airspeed you enter and the engines capacity, rpm and number of cylinders.
@Sean B I strongly disagree with the 3.77psi claim. If a point of restriction was causing a pressure difference that great the airspeed would already be well in excess of the theoretical sonic choke. In research and practice, airpseed over 350fps on single valve V8s is usually met with a dyno curve that falls off in the top end, which is why higher rpm calls for larger ports. However, there has to be a balance between low rpm airspeed as well as high. 350fps translates to 146cfm per in² of area, and that's only at 28in H²O/1psi. Simply adding in more pressure difference from increased piston speed would result in higher velocity and less density inside the port. That's the stretch I refer to. To generate that type of pressure difference would take more force as well, resulting in higher pumping losses, all leading to net loss of output. Something else to consider, a flowbench is a simple photograph of a very dynamic situation that is a running engine. In other words, a flowbench is a simple tool to help understand a very complex situation. There has to be flexibility in applying knowledge as guidelines, not set in stone rules because in some situations, some engines dont play by the rules.
@@crd-nz_001 I’m very well aware of the average airspeed numbers and max flow at those depressions. What your talking about tho is everything referenced back to 28” test pressure so we have a base to work with, that’s not the depressions the cylinder bore and port see at max rpm piston speed. Plus sonic choke can only occur at the speed of sound hence the name, what your referring to is subsonic choke when the air starts to stretch its mass, this occurs usually at mach 0.6 What happens when you test a port at 40” or even 60” test pressure? Does it all turn to shit? OR if the port is stable it flows more air? The average airspeed is only limited by the pressure differential applied to it, the pressure differential is the energy source that accelerates the air column, it especially aids in volumetric efficiency when the piston starts to slow towards the bottom of the bore and actually starts it’s way back up again, the intake valve is still open and that energy created by the pressure differential is what keeps that column of intake charge moving into the cylinder. When you see an engine on the dyno nose over it’s not because the airspeed went over 350fps, it would of went over 675fps. 350fps is just the value used on the flowbench because that’s the pressure differential that is being used.
@@crd-nz_001 just wanted to ad that no matter the pressure differential, the higher it is the less air it can flow per square inch of area, for example 10” test pressure max is 87.23cfm per/sq” yet 28” test pressure is 146cfm per/sq” so going by your theory we would want the lowest possible pressure differential to get the most air per square inch of area, the “stretch” we are talking about happens from the very beginning of applying a pressure differential, it’s when that pressure differential goes beyond 3.15/3.77psi that maintaining stability seems impossible within an engine port.
@Sean B Yes. We are saying the same thing, just in different ways. What Im trying to point out is... - It takes energy from the engine to develop a vacuum. The higher the vacuum, the higher the energy loss. - Pressure recovery does occur in the lower half of the cylinder. But, this is based on cam timing as when the intake valve shuts. - Less vacuum gives less airspeed, less ramming effect, which means cam timing needs to advance. The pressure trapped is also closer to atmospheric. The opposite for higher velocity ports. - 350fps is a balance between energy lost to creating a vacuum Vrs ramming effect. Start pushing port speed above this point, and the energy requirements to create a vacuum go up beyond the gains from the ramming effect. On a flowbench, its could well take a 18hp motor to make 60in of vacuum, yet only 3 to make 28. I am guessing the numbers, but they are not far off. I know someone needing 12Hp to buld a 40in capable bench. But that's the point Im making. Increasing port speed to beyond 350fps to increase the ramming energy to make more power is not a simple exercise. If you're making power at +600fps N/A, then you're the smartest person alive.
Hi Eric I know speed master heads are junk but what do they flow out of the box I have some that I'd get rid of. so I'd like to tell him what they flow and he can decide. I'm not asking you to flow any if you have not already flow them
Sure, 15cfm isn't necessarily worth 30hp in all cases, but better flow generally yields more power. It may put more of a bottleneck on the intake manifold of exhaust, or the cam may not be optimized for the flow, but better flow will help peak power. Sure, a 500cfm set of BBC heads would be a waste on a stock 7.5:1 200hp 454 from the mid 70s, but they'll make more power than the stock combo.
How does port volume play into this? My Mopar 360/414 stroker has ported iron heads that flow 275@600 lift but only made 460hp@5300. It made 510ft;lbs@3900. Port volume on these heads is only around 170cc. Do I need about 200-210cc's with the same flow to make more power? How do I determine port volume/area needed for 6000rpm?
So your engine made its peak power exactly where it should have going on the math, 414cubes at 5300rpm has a cfm demand of 268cfm, that is with the intake manifold bolted on. If you want peak power at 6000rpm then you need 303cfm with the intake bolted on, assuming a 2% loss from the manifold you are looking at 310cfm from your heads. When looking at minimum cross sectional area of the port you should aim for 2.25”, that’s a 95% efficiency target for that cfm/area
@@seanb250 How did you come to that conclusion? Is there a formula you use. Not questioning your expertise I just want the knowledge as I plan to replace the pistons, cylinder heads and possibly the intake manifold. I want more power.
@@ragingbull3406 start with cfm demand of your engine with this formula: cubic inches x rpm x 0.0009785 / number of cylinders 414 x 6000 x 0.0009785 / 8 = 303cfm So 303cfm is what you need at the valve after the intake manifold loss and so on, your manifold might be more than 2% loss, this is why we must flow test with the entire intake system to get the best idea. You can only flow a max of 146cfm per square inch of area at 28” test pressure so you divide the head flow required (which is 310 after manifold loss) by 146, this gives you the 100% efficiency min cross sectional area value, now you very rarely get 100% efficiency through the min so I personally aim for 95%. The area needs to be slightly larger to get that 310cfm still at 95% efficiency
@@ragingbull3406 as for port texture I favour a light burr finish, you can look on my channel to see how I do it 👍 Do you want to know how to work out the average cross sectional area?
Piston cfm requirements are different that cfm head flow requirements The area under the curve and cam timing go hand in hand No I’ve learned this the closer the head flows to meet piston cfm demand of the motor at 60-70 percent of lobe lift of the cam the more power can be made
But when you look at PipeMax's "piston CFM demand" vs. the induction system's provided air flow at each crank angle, even if you step up in intake CFM a LOT there's still a great many degrees of crank angle that the engine IS demanding more air than is being provided... -That view sure makes it look like you WILL gain more power with more CFM. None of it makes sense without velocity and cylinder fill after BDC being considered, IMHO.
I will argue that Fuel injected engines that wet flow is more important then a carburetor engine. Most people think that FI atomizes fuel better but that simply is not true.
If you're talking a throttle-body injected EFI engine vs. a carb, then I think you're 100% right. The starting droplet size just after the throttle body almost has to be much larger than just downstream of a properly setup carb. But with port injection close to the intake valve and with an injector pointing towards an open intake valve the wet flow really shouldn't matter much. (I'd think you'd still want a rough texture in the bowl area, but that should be about all that's needed AFAIK; just avoid "polishing" anything in the intake tract.) Fuel injector design (more and more smaller and smaller holes in the injector tips) and increasing fuel pressures have dramatically decreased the droplet size out of fuel injectors. In 2002 12 hole tapered injectors cam out that had a starting droplet size just out of the injector of 50 micrometers -those droplets travel from the injector through the air stream (but obviously not very far in most port applications) and they shrink as they travel as some of the fuel is evaporated off and travel past the open intake valve. "Completely atomized" is considered to be a mean droplet size of 10-20um and that should be pretty achievable with a 12 hole injector and a bit of heat in the intake / air stream and good fuel pressure. If the fuel FULLY turned into a gas, it expands dramatically and actually hurts air flow; the goal is to have it at 10-20um through the open intake valve. Chris Reynolds makes a good point that most port EFI systems ARE spraying on the back of a closed intake valve at lower loads and RPMs to help the fuel volatize-it helps keep the idle stable and makes sure the AFR doesn't spike peak on transient situations when you go from low throttle position / WoT quickly. But the current state-of-the-art port systems from Bosch that is provided to many OEMs for current lower cost port EFI engines will switch to open valve injection off idle and for as long as they can.
What I try to tell guys is. Where is the engine gona live at and what are you doing with it. Flow is just a number Port design is to make different power at different RPM. Where do you need the power. Big mud bogger. You need torque down low. Drag engine wide open power threw the RPM range. So when they get caught up in just the number and what makes the most power. But wide open throttle in a 2500lb car rowing threw the gears at 7500rpm might be what you want. But there’s different ways to make different power where you need it.
Ve has nothing to do with vacuum pumps. It has to do with port energy, wave effects, and chamber scavenging and the camshafts ability to capture the most forward flow and reject the most reverse flow. There is an organ pipe effect that for some reason old books call "ram running" even though the wave is running through the air and it's not a wave of air ramming into the cylinder the formulas presented under "ram tuning" are clearly sound wave timings as they only look at lengths. There is a Helmholtz effect that is often confused with the organ pipe effect but is different which has to do with delays of accelerating air and decelerating air coupled to the piston with a springy air volume. And there is also port energy based on average velocity and mass which has a lot in common with hemholz effects. There are also tapered pipe effects that aren't described in the old literature and seemed almost like voodoo requiring trial and error. When you stack the right combination of measurements and get cam lobe phasings working at the same speed you get more Ve and torque. Parasitics in the intake and exhaust can affect the Ve probably more than actual "pumping loss." It's more losses of pumping by way of losses to pumping than actual losses to pumping alone. When saying that an engine needs x cfm it needs to be qualified in so many ways because the cylinder is gonna be filled with something it's the density of everything in there and the amount of contamination by spent exhaust gasses that change. A super flow Dyno may use a flow meter with a fan mounted on an encoder that's been calibrated for airspeed through the diameter of the unit. The speed gives length and time information to convert to cfm. Pipe max will tell you that if you expect the superflow dyno to read 108% Ve then cfm is actually moving but it's not telling you precisely what Ve you should get for the cfm which can be estimated but can't exactly be known outside of the Dyno without every dimension down to the camshaft profile. It's not telling you exactly how that cfm value affects the Ve so it might make you say sure that's enough but it's not eliminating the benefits of having more. When cfm is tested on a flow bench there is a test pressure and there is a density change associated with that test pressure. If you're using a 28in test pressure that's about 1psi or about 6-7% loss of air density. There is reason right there to say that you could infact be giving away 50hp by not having more flow. Again it gets more complex because of the complex pressure curve due to above reasons. But also because the valve is open more than 180 degrees but many of those degrees are partial so you'd actually have to multiply the flow curve by the lift curve and find the degree-flow under that curve and decide if you are giving up Ve based on that number. But it gets complicated more still because often when you have that you end up with an engine that's lazy down low and wants to rev much higher and your giving away something by having power in an rpm you don't intend to use or the intake runners get too long for that rpm. Eventually port limiting velocity because of a limit in valve size or an obstruction like a pushrod or some manifold rule requirement makes it impossible to flow more air because it doesn't go supersonic this happens no matter what the flow says and eventually the sound wave tuning makes it so you can't get through the valley to the peak where the next harmonic exists. So maybe a person should go by port limiting velocity and runner lengths and try to get as much flow as possible in that space so long as there isn't a loss in port energies. Having more flow at the valve should increase port energies up stream but adding excess volume to get there will decrease energies in the head. Pipe max is good for manifold and header length selection but you might also want David vizards software that plots port energy based on volume and flow. There is no reason you can't use the manifold runner as part of you port for these comparisons... I can't remember exactly if pipe max does port energy. It seemed like a better tool for building exhaust or choosing intakes because it shows the pipe harmonics.
I've always had a theory that the reason why a "theoretically too big" carb makes a little more horsepower. Having "Just enough air flow" might allow the air to go in, but it's flow characteristics might be "dirty" instead of smooth and steady. By opening the orifice to a larger size it allows the air to equalize easier between any of the small low/high pressure zones on the carburetor's surface areas or any small edges, basically where air may have to slow down and/or change direction abruptly to get "in with the crowd" of flowing air. Just my theory, but this could explain why a full addition of 200cfm might gain just 4-8 hp. As it's not the cfm gaining power, but a more smooth/predictable airflow route for a greater percentage of the existing airflow. Ultimately adding efficiency. Does this align with what you're explaining in the video?
Guess: "More CFM is better at the correct CSA for your engine size and RPM goals". (Now to actually watch the video; lol!). The episode description sounds shockingly similar to a Darin Morgan quote...
Everyone knows that the Ford Cleveland V2 heads (small valve) makes much better torque than the V4 (big valve) heads. The V4 heads only beat the V2's above 6000RPM where nobody actually drives...
CFM is not a universal amount... The math done to to figure out how much air an engine will use is mechanical cfm .... What you test on the bench is a pressure drop cfm ... Carbs are tested at different pressure drop then heads and the engine certainly doesn't run at a 28 inch pressure drop you can't compare the different numbers because they are not all the same !
@@WeingartnerRacing but with rpm all engines are variable displacement ... More cfm more power and more rpm as long as the intake flow and carburetor flow will keep up ...if you hit a ceiling it's because they are not
Why do you Port ?..... What does Porting do ? ....Ever heard of Static vs Dynamic Compression ? Static Compression is Measuring & CCing , Pistons, Chambers, , Gaskets, Deak height ! Static Dynamic Compression is a Running engine , ...Flowing Air & Fuel ... measure of Compression ! More Flow creates HIGHER Dynamic Compression , Starts with .....RING Seal.... of course you have to have the Right CAM Timimg to Open and Close at the Right Time to capture the Air & Fuel Mix ? Exhaust Open and Close Timing Critcial too Piston on Intake Stroke creates a Depression ...Outside Air rushs in @ DA to fill the Low Pressure VOID ? No Vaccum.., Just Mother Nature ? More Port Flow {Captured} Raises ....Dynamic Compression ...& Increases VE ? 100% to 130% VE with Inertial-Supercharging WAVES bouncing of the back of Intake Valve while Closed ??? Pumping Loss is Piston Drag, Ring Drag, Crank-Rods, Wrist Pins, Oil Pump Friction, Oil Windage, Oil Drain, Spring Friction, Cam - Lifters, Rocker Arms Frictions, Water Pump Friction ?
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I believe the correct term for this is "realized power". If you keep increasing the cylinder-head flow capability (cfm) and you keep getting measurable increases in power, then you are seeing "realized power" gains. If the last increased cylinder-head flow increase does not add to the power output, then you have reached the maximized power output (from the cylinder-head's contribution) for that particular engine configuration.
ALL cylinder-heads are a restriction to an engine's Intake airflow requirements for true 100% cylinder-filling. We can know this by looking at the fact that the only way to theoretically completely flow at the rate of the piston's descent, would be to take the cylinder-head off of the block-deck completely during the intake stroke, then immediately replace it at Bottom-Dead-Center before the piston rises again. Even if the cylinder-head was only equipped with a single valve located dead-center over the piston, as an intake valve, it could not flow the full volume needed. With that as the baseline for maximum cylinder-filling (and therefore maximum potential power output) we can see that there are many limitations to maximum power between the cylinder bore and the throttle-body (which should be the only, and variable, "chokepoint"/or throttle) in the entire induction system.
I believe that all naturally aspirated engines (and most supercharged ones as well) are airflow-limited to what amounts to a smaller displacement engine, in realized power. One clue to this is that we never seem to achieve maximum potential output from any given engine size. Most builders go with bigger engine size or displacement to get the desired or needed power increase.
The best way to maximize any particular engine's output is to use experience (our own or from someone reputable) to get you close, then "cut & try" to get the true best output from it. This is tedious and time-consuming and of course expensive to do. That is why most of us will have to settle for some power output level somewhat better than average, without ever realizing the absolute maximum that could be achieved with that engine configuration. That is what makes this profession or hobby fun. Learning and enjoying the fruit of our experience while trying to achieve the best possible performance. If someone were to figure out the absolute best combination for every possible bore/stroke combination, it would ruin the sport for the rest of us I believe. If you are one that has figured it all out, I know I probably won't have to ask you to "keep it to yourself"!
The voice over is great for this kind of discussion because it makes it easier to focus on what you’re explaining. For other topics, it helps to have you show and say simultaneously. More specifically, when you tell stories or talk about PRI or shop tours, we want to hear and see your body language. You were clearly more even toned in the voice over, but your personality and enthusiasm show up more when you are physically on camera.
You said you appreciate us taking our time to watch this... but I appreciate you taking your time to show us
Interesting info Eric!
You just answered a few long standing questions I've had. I recall asking about stuff relating to this in a previous comment. If I wasn't 60 and on a limited income, I'd be personally traveling to your shop with heads in hand!
Wish we had easy access to guys like you with your knowledge and skills back when I was in the middle of all this.
Keep the quality info flowing! (pun intended) The more, the better.....lol
Thanks again for a very informative video, all the best to you and your loved ones
Good information👍I totally agree with everything you said.Really like the technical discussions on subjects not talked about much the most.Thanks🙏🙏
Makes sense. You do as you feel as far as videos go. This fellers not picky, I simply value the knowledge you pass on. Thanks again.
Great vid. I think many people don't understand the acoustic resonance in the intake, and the port as a wave, that starts, and stops moving, speeding up, and slowing down, and how size, shape, taper and radius of the intake runner all compound the complexities of them. Making a powerful naturally aspirated engine is harder than bolting on boost.
Hi Eric.
Thanks for the video. This is something I'm looking at now for a 383 I'm designing for my son. You confirmed the numbers I came up with. It's been 30+ years since I've done this so it's a big memory and learning curve.
Thanks for the help.
Now about the talk-over format. Personally, it doesn't work for me. I'm pretty sure I stick with the videos to the end or close to it.
I'm just a majority of one so if the others like it I'll keep watching.
Keep up the good work.
About voiceover: the audio is higher volume and more consistent,,, altho there is a super minor hiss noise,,, like software compression hiss. Go to 1:17 amd listen closely,,, but both are good,,, voiceover usually more concise and organized format for us sometimes audio only subscribers
You are missing a key consideration. Time. Ultimately Torque is a function of Time X CFM. The time is in the camshaft. You can make the same power with a smaller cam and head that can flow better. Camshaft timing has its limits, such as drivability, emissions and operating RPM. There is also a modulus, for port size and runner length, a smaller port will have less volume or weight that needs to be re-accelerated when the valve starts to open so it will respond better to transients and lower speed operation. So you have to pick a cam (time) and work backwards. The smallest port with the most flow will offer the best transients. Dyno doesn't value transients which is why many dyno hero motors do nothing on a road track where the driver needs throttle response to transfer load and steer the the car.
You hit the nail VERY HARD ON THE HEAD.......
I always say : a dyno revving up 500rpm/sec ........... That takes 4 seconds from 6000 to 8000 rpm..... Thats too slow.
Nobody uses calenders measuring accelaration....
Circle track guys had this figured out decades ago, people read magazine articles and get caught up in big CFM, big peak Dyno hp numbers, put it together and wish they had left it stock, there's a good reason for the compression and gearing/stall recommendations given for shelf cams the bottom of the page guys usually spend a lot of money to make the car go slower. I'd venture a guess and say that 90% of the street car crowd would be happier with more cubic inches, even if it shows less peak hp will run, drive, and accelerate from idle to 4000 great.
If you think that the best racers out there, regardless, what kind of racing road race drag race whatever if you think that the most successful people do not use a dyno Engine or chassis you are wrong by a mile they’ve been using them for decades and decades, I know you don’t seem to like them or respect them for some reason but you’re just plain wrong
Are you trying to say overlap determines the rpm where peak efficiency occurs for a given combo? In my mind, cfm is the second concern behind velocity, yet both are critical for best output..
I do agree somewhat. I left the cam part out because it really could make a series of videos not something to just throw in this one. The smallest port that flow the most I have addressed in previous video. It’s really in what rpm range you want to accelerate that determines port size. Thanks for the comment.
I attempted to contact today, and tonight I hit on this video!!!
When the carburetors larger on a motor like that if you are after straight power and not drivability, you go as big as you can wear it functions properly. It does come down to again pumping losses, as you stated like the ports. Due to the design of a carburetor it will always have some type of pumping losses due to the Venturi design. They actually tested this theory an engine power and showed the engine had less vacuum at high rpm so I can only attribute this to pumping losses. We are talking very small amounts, however.
I like your vids, I think stuff like this tends to be lacking sometimes in Engine Building (Hot Rod mags/marketing). I'm new to all of this, and learning. In reading Smokey Yunicks book, he talked about the whole system being a Venturi into a Venturi into a Venturi to keep velocity up. Interesting theory. I'm learning in a wierd but Interesting way, lol. Building TQ in a Jeep 258 (Dyno'ing 3 heads, stock, 7120 4.0 and the Edelbrock 50169). For me and Jeeps, over carb'ing and too much flow has been an issue. As us normal Jeep guy's are only working within 800-3,500 RPM. A cam is next, but sticking with my little Weber 38- custom Aux Vent's and I ground downed the Emulsion tube.
Great info to know
Bust them myths.
Love these videos.
I have noticed on our asphalt circle track car that is a 358 big boar small stroke 12.5 compression engine when we rum Winchester speedway if I put a carburetor that flows 965 cfm we will pick up 4 tenths over our regular 850 cfm carburetor
Thank you for the video
Thanks again
Sorry Eric I've missed a few videos. I've argued oversized throttle bodies for 20 years. LOL!!! Good stuff Eric. Separates us educated from the forum kings.
Very true what you say....
Right on
I dont know a lot about cylinder heads , what I have learned is from my limited experience. I built a small block chev a 302 a long time ago for my 68Camaro a four speed manual. I bought a set of heads that came off a g gas car that sent a Monza to I think 9.98 at one time . I built the engine in I think 1980 so the heads came off a car before then . At any rate I built a engine capable of turning 7800 or so and stay together. It ran hard all the way to the Rev limiter. It would have made power past that if I had the bottom end to go there . For me on a hot rod I want the engine to pull hard and not lay over . Heads is one area I try to get the best I can to do what I want . So I just ask the porter what do I need to make this much power . Lastly I rather have a really good set of heads and a little less cam to accomplish the same results. Thanks for your good advice
Great topic.
How'd this work on the stock heads in my 1988 4.3 powered S10?
....maybe add some Manley race flow valves and change the exhaust to 1.6 before porting.
What, 50hp? 😁
Very enlightening video 👍
Eric I know you know about the short side choke on the ls3 or ls7 heads, that is for wet flow at low rpm.
Lots of good info in this one. Engines do not pull air into the cylinder.
All about knowing that rpm you want it to work at sometimes the mild head with the right cam goes really well . But at a pro race build we know that larger port and cfm will make what rpm we want , with the cam it needs , every single build needs its heads to suit, simple
4:44 the soot comes from the EGR and PCV… get rid of the egr and add an oil catch can to the PCV and your engine will run a lot cleaner
Can you do a video on the effects of the different camshaft diameters of LS, SBC, BBC, SBF, Modular Fords?
Hey, sorry to comment again, lol. Do you have any vids on building TQ? I'm VERY interested in how to keep a high velocity flow on smaller ports, such as just port matching the roof of ports/matching intake with top of port and no grinding? I am working with an inline 6. Would this help the intake to keep the Velocity up, especially with a carb for low RPM TQ.
And do you have vids on intake mods? I've rounded out the bottom of the intake where the Carb sits, to allow more flow, not sure it made a difference, lol. Like an inverse Velocity stack, sort of, which I know stacks work, as I've seen it testing with Smoke- tried to increase CFM on a Weber 38, it was a fail, lol.
The bigger the cylinder diameter, the more area on overlap for the scavange to fill, the more cross section you need, stroke just adds VE after the scavange.
im more thinking like .. if i port a top. i need to do something about the entire exhaust system also.. also the intake system. And a new engine... better springs. and a more aggresive cam to gain something.
I'm stuggling with this right now myself... doing a small block mopar just for beating on the street and having fun... not a lot of head choices and i really want TFS heads but they are overkill by a mile, the choices below that are not much cheaper but not near as good either.. for something that will rarely see over 6k rpm, not sure where i should throw money at this point..
@WeingartnerRacing can you do a video showing flowrates against depression on an orifice just to see that relationship? Several people will automatically go “yeah but a Holley is measured at 1.5” and that’s a restriction”
Head flow in the auto community is like power ratings in the audio world. How many watts? It's easy to measure I suppose so you gotta have a number to throw out there.
Too many are too concerned with them almighty flow numbers! There's also port velocity that you might want to be more concerned with, in my opinion anyways. I'm no professional head porter by no means whatsoever but I've read a lot of books on the subject from people such as David Vizard and such. Maybe explain that to people!? Great videos guy!
Does increasing port volume decrease carb signal strength?
Good Vid
Thanks
@@WeingartnerRacing thank you for these videos so much good information on heads not everyone generally uses. I have a set of these 230cc cnc Trick Flows and basically took them out of the box and bolted them to a 406ci. It made decent power with a unported super victor and a street roller cam.
Port velocity air speed rules 295 to 340
We often forget that carburetors, Holley 4 barrel style at least originally got their cfm rating @ 1.5”hg. That’s 20.4” water. Making best power we want to reduce vacuum to a minimum at WOT to allow greatest air/fuel density to increase power. If a larger carb such as Eric’s 1000cfm drops WOT vacuum to .7”hg then what would that carb flow @ .7”hg or 9.5” water? Surely a less cfm figure but we are hung up on the flow number @ 1.5”hg. Most carb experts don’t talk cfm but rather dimensions of venturi, throttle bore and venturi to throttle bore ratios. It’s phenomenally difficult to get people to understand engines operate off density and not cfm. A carburetor is a density regulating device, not cfm changing device.
If you getting 108 then great job!
AFR told me no.I talked to Adam at AFR when building my 406.We talked about the 195’s and the 210’s.With the cam I am running and gear ratio and what I plan to do with it,Adam had said I was borderline.Mention one of the issues,,if I ran the 210’s I might zing the RPM’s A little to quick.So I was borderline.
I don’t want to out RPM my torque ban.Kind of make sense.
Correct!….
Where can a calculator be found for determining head flow needed?
I'm building a ~13:1 LS 402 and have LS3 head, but can more easily keep the compression up if flow from say a ported 243 is enough.
Maxrace software called Pipemax
what was the name of the program you talk about, PipeMags or something?
Pipemax
All other things being equal, would you select a larger flowing head for a methanol drag race BBC than one for race gas?
Thanks!
I do end up going slightly larger for methanol.
@@WeingartnerRacing So there IS a replacement for air displacement (increase in CSA). -Terrible attempt at a pun... I'll go iron my hands now...
We see cfm numbers for intake or exhaust flow and infer results, but the actual flow characteristics are dynamic, not static. Further, exhaust flow can have a huge impact on intake flow (remember the 5-cycle cam from Isky?). Flow through the carb or throttle body is mostly the average of what’s going on in the cylinder head. So steady state flow from a flow bench gives you a piece of data, but it’s not the total answer! The dyno, on the other hand, gives you the actual result! Can’t wait to see some comparisons with The Mule!
Let’s do some math. At 6000 rpm an engine has 50 intake cycles for each cylinder every second, or one every 20 milliseconds. The intake valve might be open for 250° out of 720°, so that is roughly 7 ms. The 400 cu in engine has eight 50 cu in cylinders, so in the 108% VE engine we have 7 ms to move 0.029 cu ft of air. That equates to an average flow of roughly 250 cfm, but flow doesn’t turn on and shut off in a square wave. If it moved as a sine wave, the average could be around 0.636 of the peak, or 390 cfm. We use clues like the flow bench to help determine the best way to make power, but the numbers only reflect a part of whole. The running engine tells the final story. Thanks for this video, Eric, it’s a good one!
Eric I see you show a pic of the Trick flow twisted SBC head, have you flowed that head and have you used them at all?
No it was at the auction yesterday. I bid on it but it went for $300. I gave the guy my card to flow it.
I see a lot of those for sale on marketplace, are they underrated perhaps?
@@stevenbelue5496 the original g1 with canted valves was not a good design, they tried to design it to work with special rockers, they had problems, had trouble with the guides. There is a reason they stopped making and selling them. Haven't heard much about the g2 twisted wedge sbc heads
@Dick Head Listen, no need to be a d!ck. You don't know the who story and maybe he offered to flow it for free.
@@stevenbelue5496 Well like anything else, if you pay close attention to your valve train Geometry, I think they can be made to work fine. And with some minor port work I am sure they will make great power.
More cfm is better if you can take advantage of it.
I see a cantive valve sbc head do you like those kind of heads
Yes
I think , the factory LS3 head flows enough to support any fast street type car, any more work done then that is wasted unles you want all out race car. its already been shown to support over 700 hp untouched.
My 2 cents.
Peak cylinder head flow is demanded by the pistion, and when does said piston reach its peak speed? Around 70-75 degrees crank duration. Or, probably around when the cam is in the 0.4in range. As you have seen and tested, improvements in airflow here are attributed to improvements in output.
Next information drop, Pipemax has a function of calcuating cfm from piston speed. It brings up a large spreadsheet showing, piston speed, crank angle, rod angle, and cfm demanded by the piston.
Waaay back in 2006, I ran a simulation using Pipemax on a 1600cc engine. It stated that for a 400cc cylinder, its piston cfm demand was 275cfm@8250rpm. If that was doubled to an 800cc cylinder (for a 6.4L V8), I would guess cfm demand would also double to 550cfm@8250rpm.
We also have to understand that a flowbench operates at 28in of H²O, where a piston can generate far greater depressions than this. This stretching air is an invisible friction torque loss, and one way to lower it is by adding more cfm to the cylinder head. In a nutshell, this is where a pumping loss can be easily fixed because adding a better flowing head reduces the "strecth on the air." It's also why a cam change is needed, as the strech into the port is less, meaning less velocity. So, an earlier intake closing point is needed (big head small cam V small head big cam debate)
Its also the theory on why Ford made the 4V Cleveland head. Small cam, big head.
As a side note, the moment manifold vacuum hits 1.5in of Hg, there is effectively 13.7psi entering the cylinders. 1psi loss = 7.5% less air mass. The volume is the same, but it has less weight. Installing a bigger carburetor helps bring back that loss. There are other factors that then come into play, like running a finer grain booster because less vacuum means the fuel is harder to vaporize and stay atomized. This may theoretically be why a 1000cfm carby returns improvements over the 830ish one you said.
Pressure differential is what makes air move, yes peak piston speed will create the highest pressure differential but as long as that pressure differential is kept below 3.77psi then you won’t be stretching any air causing it to reduce its density.
The pressure differential determines what the average airspeed is within the port and as long as your under 3.77psi pressure differential then the minimum cross sectional area won’t go into choke.
Pipemax gives you a number at 28” test pressure as a reference to go against, this reference is calculated across what average airspeed you enter and the engines capacity, rpm and number of cylinders.
@Sean B I strongly disagree with the 3.77psi claim. If a point of restriction was causing a pressure difference that great the airspeed would already be well in excess of the theoretical sonic choke. In research and practice, airpseed over 350fps on single valve V8s is usually met with a dyno curve that falls off in the top end, which is why higher rpm calls for larger ports. However, there has to be a balance between low rpm airspeed as well as high.
350fps translates to 146cfm per in² of area, and that's only at 28in H²O/1psi. Simply adding in more pressure difference from increased piston speed would result in higher velocity and less density inside the port. That's the stretch I refer to. To generate that type of pressure difference would take more force as well, resulting in higher pumping losses, all leading to net loss of output.
Something else to consider, a flowbench is a simple photograph of a very dynamic situation that is a running engine. In other words, a flowbench is a simple tool to help understand a very complex situation. There has to be flexibility in applying knowledge as guidelines, not set in stone rules because in some situations, some engines dont play by the rules.
@@crd-nz_001 I’m very well aware of the average airspeed numbers and max flow at those depressions.
What your talking about tho is everything referenced back to 28” test pressure so we have a base to work with, that’s not the depressions the cylinder bore and port see at max rpm piston speed.
Plus sonic choke can only occur at the speed of sound hence the name, what your referring to is subsonic choke when the air starts to stretch its mass, this occurs usually at mach 0.6
What happens when you test a port at 40” or even 60” test pressure? Does it all turn to shit? OR if the port is stable it flows more air? The average airspeed is only limited by the pressure differential applied to it, the pressure differential is the energy source that accelerates the air column, it especially aids in volumetric efficiency when the piston starts to slow towards the bottom of the bore and actually starts it’s way back up again, the intake valve is still open and that energy created by the pressure differential is what keeps that column of intake charge moving into the cylinder.
When you see an engine on the dyno nose over it’s not because the airspeed went over 350fps, it would of went over 675fps. 350fps is just the value used on the flowbench because that’s the pressure differential that is being used.
@@crd-nz_001 just wanted to ad that no matter the pressure differential, the higher it is the less air it can flow per square inch of area, for example 10” test pressure max is 87.23cfm per/sq” yet 28” test pressure is 146cfm per/sq” so going by your theory we would want the lowest possible pressure differential to get the most air per square inch of area, the “stretch” we are talking about happens from the very beginning of applying a pressure differential, it’s when that pressure differential goes beyond 3.15/3.77psi that maintaining stability seems impossible within an engine port.
@Sean B Yes.
We are saying the same thing, just in different ways.
What Im trying to point out is...
- It takes energy from the engine to develop a vacuum. The higher the vacuum, the higher the energy loss.
- Pressure recovery does occur in the lower half of the cylinder. But, this is based on cam timing as when the intake valve shuts.
- Less vacuum gives less airspeed, less ramming effect, which means cam timing needs to advance. The pressure trapped is also closer to atmospheric. The opposite for higher velocity ports.
- 350fps is a balance between energy lost to creating a vacuum Vrs ramming effect. Start pushing port speed above this point, and the energy requirements to create a vacuum go up beyond the gains from the ramming effect.
On a flowbench, its could well take a 18hp motor to make 60in of vacuum, yet only 3 to make 28. I am guessing the numbers, but they are not far off. I know someone needing 12Hp to buld a 40in capable bench.
But that's the point Im making. Increasing port speed to beyond 350fps to increase the ramming energy to make more power is not a simple exercise.
If you're making power at +600fps N/A, then you're the smartest person alive.
Hi Eric
I know speed master heads are junk but what do they flow out of the box
I have some that I'd get rid of. so I'd like to tell him what they flow and he can decide. I'm not asking you to flow any if you have not already flow them
They changed designs often so it depends on which ones.
Sure, 15cfm isn't necessarily worth 30hp in all cases, but better flow generally yields more power. It may put more of a bottleneck on the intake manifold of exhaust, or the cam may not be optimized for the flow, but better flow will help peak power.
Sure, a 500cfm set of BBC heads would be a waste on a stock 7.5:1 200hp 454 from the mid 70s, but they'll make more power than the stock combo.
How does port volume play into this? My Mopar 360/414 stroker has ported iron heads that flow 275@600 lift but only made 460hp@5300. It made 510ft;lbs@3900. Port volume on these heads is only around 170cc. Do I need about 200-210cc's with the same flow to make more power? How do I determine port volume/area needed for 6000rpm?
So your engine made its peak power exactly where it should have going on the math, 414cubes at 5300rpm has a cfm demand of 268cfm, that is with the intake manifold bolted on.
If you want peak power at 6000rpm then you need 303cfm with the intake bolted on, assuming a 2% loss from the manifold you are looking at 310cfm from your heads. When looking at minimum cross sectional area of the port you should aim for 2.25”, that’s a 95% efficiency target for that cfm/area
@@seanb250 How did you come to that conclusion? Is there a formula you use. Not questioning your expertise I just want the knowledge as I plan to replace the pistons, cylinder heads and possibly the intake manifold. I want more power.
@@ragingbull3406 start with cfm demand of your engine with this formula: cubic inches x rpm x 0.0009785 / number of cylinders
414 x 6000 x 0.0009785 / 8 = 303cfm
So 303cfm is what you need at the valve after the intake manifold loss and so on, your manifold might be more than 2% loss, this is why we must flow test with the entire intake system to get the best idea.
You can only flow a max of 146cfm per square inch of area at 28” test pressure so you divide the head flow required (which is 310 after manifold loss) by 146, this gives you the 100% efficiency min cross sectional area value, now you very rarely get 100% efficiency through the min so I personally aim for 95%.
The area needs to be slightly larger to get that 310cfm still at 95% efficiency
@@seanb250 Got it! Now how do I determine what cylinder head port surface/cross sectional area I need for that 303cfm? Thanx.
@@ragingbull3406 as for port texture I favour a light burr finish, you can look on my channel to see how I do it 👍
Do you want to know how to work out the average cross sectional area?
Piston cfm requirements are different that cfm head flow requirements
The area under the curve and cam timing go hand in hand
No I’ve learned this the closer the head flows to meet piston cfm demand of the motor at 60-70 percent of lobe lift of the cam the more power can be made
Did you say the .100-.200 lift doesn’t matter please explain
That’s were reversion happens most and hopefully you are blasting past that point.
But when you look at PipeMax's "piston CFM demand" vs. the induction system's provided air flow at each crank angle, even if you step up in intake CFM a LOT there's still a great many degrees of crank angle that the engine IS demanding more air than is being provided... -That view sure makes it look like you WILL gain more power with more CFM. None of it makes sense without velocity and cylinder fill after BDC being considered, IMHO.
I will argue that Fuel injected engines that wet flow is more important then a carburetor engine. Most people think that FI atomizes fuel better but that simply is not true.
GM SFI engines spray fuel on the back of a closed valve at lower loads and rpm.
If you're talking a throttle-body injected EFI engine vs. a carb, then I think you're 100% right. The starting droplet size just after the throttle body almost has to be much larger than just downstream of a properly setup carb. But with port injection close to the intake valve and with an injector pointing towards an open intake valve the wet flow really shouldn't matter much. (I'd think you'd still want a rough texture in the bowl area, but that should be about all that's needed AFAIK; just avoid "polishing" anything in the intake tract.)
Fuel injector design (more and more smaller and smaller holes in the injector tips) and increasing fuel pressures have dramatically decreased the droplet size out of fuel injectors. In 2002 12 hole tapered injectors cam out that had a starting droplet size just out of the injector of 50 micrometers -those droplets travel from the injector through the air stream (but obviously not very far in most port applications) and they shrink as they travel as some of the fuel is evaporated off and travel past the open intake valve. "Completely atomized" is considered to be a mean droplet size of 10-20um and that should be pretty achievable with a 12 hole injector and a bit of heat in the intake / air stream and good fuel pressure. If the fuel FULLY turned into a gas, it expands dramatically and actually hurts air flow; the goal is to have it at 10-20um through the open intake valve.
Chris Reynolds makes a good point that most port EFI systems ARE spraying on the back of a closed intake valve at lower loads and RPMs to help the fuel volatize-it helps keep the idle stable and makes sure the AFR doesn't spike peak on transient situations when you go from low throttle position / WoT quickly. But the current state-of-the-art port systems from Bosch that is provided to many OEMs for current lower cost port EFI engines will switch to open valve injection off idle and for as long as they can.
My suggestion is to do what a works for u. If voice over is easy then do that if not keep recording on the fly
What I try to tell guys is. Where is the engine gona live at and what are you doing with it. Flow is just a number Port design is to make different power at different RPM. Where do you need the power. Big mud bogger. You need torque down low. Drag engine wide open power threw the RPM range. So when they get caught up in just the number and what makes the most power. But wide open throttle in a 2500lb car rowing threw the gears at 7500rpm might be what you want. But there’s different ways to make different power where you need it.
Ve has nothing to do with vacuum pumps. It has to do with port energy, wave effects, and chamber scavenging and the camshafts ability to capture the most forward flow and reject the most reverse flow. There is an organ pipe effect that for some reason old books call "ram running" even though the wave is running through the air and it's not a wave of air ramming into the cylinder the formulas presented under "ram tuning" are clearly sound wave timings as they only look at lengths. There is a Helmholtz effect that is often confused with the organ pipe effect but is different which has to do with delays of accelerating air and decelerating air coupled to the piston with a springy air volume. And there is also port energy based on average velocity and mass which has a lot in common with hemholz effects. There are also tapered pipe effects that aren't described in the old literature and seemed almost like voodoo requiring trial and error. When you stack the right combination of measurements and get cam lobe phasings working at the same speed you get more Ve and torque. Parasitics in the intake and exhaust can affect the Ve probably more than actual "pumping loss." It's more losses of pumping by way of losses to pumping than actual losses to pumping alone. When saying that an engine needs x cfm it needs to be qualified in so many ways because the cylinder is gonna be filled with something it's the density of everything in there and the amount of contamination by spent exhaust gasses that change. A super flow Dyno may use a flow meter with a fan mounted on an encoder that's been calibrated for airspeed through the diameter of the unit. The speed gives length and time information to convert to cfm. Pipe max will tell you that if you expect the superflow dyno to read 108% Ve then cfm is actually moving but it's not telling you precisely what Ve you should get for the cfm which can be estimated but can't exactly be known outside of the Dyno without every dimension down to the camshaft profile. It's not telling you exactly how that cfm value affects the Ve so it might make you say sure that's enough but it's not eliminating the benefits of having more. When cfm is tested on a flow bench there is a test pressure and there is a density change associated with that test pressure. If you're using a 28in test pressure that's about 1psi or about 6-7% loss of air density. There is reason right there to say that you could infact be giving away 50hp by not having more flow. Again it gets more complex because of the complex pressure curve due to above reasons. But also because the valve is open more than 180 degrees but many of those degrees are partial so you'd actually have to multiply the flow curve by the lift curve and find the degree-flow under that curve and decide if you are giving up Ve based on that number. But it gets complicated more still because often when you have that you end up with an engine that's lazy down low and wants to rev much higher and your giving away something by having power in an rpm you don't intend to use or the intake runners get too long for that rpm. Eventually port limiting velocity because of a limit in valve size or an obstruction like a pushrod or some manifold rule requirement makes it impossible to flow more air because it doesn't go supersonic this happens no matter what the flow says and eventually the sound wave tuning makes it so you can't get through the valley to the peak where the next harmonic exists. So maybe a person should go by port limiting velocity and runner lengths and try to get as much flow as possible in that space so long as there isn't a loss in port energies. Having more flow at the valve should increase port energies up stream but adding excess volume to get there will decrease energies in the head. Pipe max is good for manifold and header length selection but you might also want David vizards software that plots port energy based on volume and flow. There is no reason you can't use the manifold runner as part of you port for these comparisons... I can't remember exactly if pipe max does port energy. It seemed like a better tool for building exhaust or choosing intakes because it shows the pipe harmonics.
Vacuum pumps help ve because it helps the rings to seal better hence more torque and ve.
I've always had a theory that the reason why a "theoretically too big" carb makes a little more horsepower.
Having "Just enough air flow" might allow the air to go in, but it's flow characteristics might be "dirty" instead of smooth and steady.
By opening the orifice to a larger size it allows the air to equalize easier between any of the small low/high pressure zones on the carburetor's surface areas or any small edges, basically where air may have to slow down and/or change direction abruptly to get "in with the crowd" of flowing air.
Just my theory, but this could explain why a full addition of 200cfm might gain just 4-8 hp.
As it's not the cfm gaining power, but a more smooth/predictable airflow route for a greater percentage of the existing airflow. Ultimately adding efficiency.
Does this align with what you're explaining in the video?
Guess: "More CFM is better at the correct CSA for your engine size and RPM goals". (Now to actually watch the video; lol!). The episode description sounds shockingly similar to a Darin Morgan quote...
People need to hear it more.
@@WeingartnerRacing Preach on! (Fully agreed!)
I've never seen a fuel injection engine not make more power with more cfm throttle body. Just depends on what drivabilaty you are willing to deal with
Yes but not as much as the added cfm would show. Usually it’s small gains.
Anyone consider ,feet per second air speed ? Lol
Everyone knows that the Ford Cleveland V2 heads (small valve) makes much better torque than the V4 (big valve) heads. The V4 heads only beat the V2's above 6000RPM where nobody actually drives...
CFM is not a universal amount... The math done to to figure out how much air an engine will use is mechanical cfm .... What you test on the bench is a pressure drop cfm ... Carbs are tested at different pressure drop then heads and the engine certainly doesn't run at a 28 inch pressure drop you can't compare the different numbers because they are not all the same !
I was comparing them by saying the additional airflow didn’t really add the power because it was way more than the motor needed.
@@WeingartnerRacing but with rpm all engines are variable displacement ... More cfm more power and more rpm as long as the intake flow and carburetor flow will keep up ...if you hit a ceiling it's because they are not
Why do you Port ?..... What does Porting do ? ....Ever heard of Static vs Dynamic Compression ?
Static Compression is Measuring & CCing , Pistons, Chambers, , Gaskets, Deak height ! Static
Dynamic Compression is a Running engine , ...Flowing Air & Fuel ... measure of Compression ! More Flow creates HIGHER Dynamic Compression , Starts with .....RING Seal.... of course you have to have the Right CAM Timimg to Open and Close at the Right Time to capture the Air & Fuel Mix ? Exhaust Open and Close Timing Critcial too
Piston on Intake Stroke creates a Depression ...Outside Air rushs in @ DA to fill the Low Pressure VOID ? No Vaccum.., Just Mother Nature ?
More Port Flow {Captured} Raises ....Dynamic Compression ...& Increases VE ? 100% to 130% VE with Inertial-Supercharging WAVES bouncing of the back of Intake Valve while Closed ???
Pumping Loss is Piston Drag, Ring Drag, Crank-Rods, Wrist Pins, Oil Pump Friction, Oil Windage, Oil Drain, Spring Friction, Cam - Lifters, Rocker Arms Frictions, Water Pump Friction ?