Only 41k views? This video is so under rated and full of useful information. Thank you Dsport, for taking the time to nourish us car geeks with this information
Higher compression in boosted applications definitely has its place more compression means you can make the same power with less boost and get faster spoil I think That's why things are really going that direction nowadays
@@ccclc6159 Diesel cycle has different thermodynamics and different combustion process(Heterogeneous). He is talking about compression ratio in otto cycle(Petrol) engines.
@@metaphorpritamhey dingdong did I mention diesel? he says pump gas and e85 in the first 30seconds, early farm tractors usually came with gasoline or propane engines, propane tractors had higher compression pistons installed so they would make about the same hp as the gas version, btw what is a diesel cycle? do you think there is a gas vs diesel cycle?
XR650L - 2009 version. 8.3 going to 10.2 on local pump gas 95 Octane - should be a sweet spot. Smoking hopium until things turn out right. Cool channel. Greetings from DBN.
Great video !!! You really didn’t addressed noc psi or NA engines or the math behind it, however this was awesome I think if you added a tiny bit of animated grafix and charts we would all understand allot better
As the unswept volume decreases with increasing CR , swept volume increases as well .. total volume remains constant . At 9:13/9:42 you call 2nd column unswept , later 10:19 calling it swept !!!
That is not correct. You have two segments that need to be looked at separately. The swept volume is only the distance between the piston top and the edge of the block when the piston is at BDC. The chamber volume (unswept) is a separate thing and when you change that volume, the swept volume doesn't change. But when you look at the combination of both (total volume) and you reduce the chamber volume to increase CR, the total volume decreases by the amount the chamber volume was reduced. Has no effect on the swept volume portion though.
The definition for engine displacement is flawed. Bore and stroke is not the total volume or displacement of a engine. To exclude the piston hight, the un-swept, or (combustion chamber), makes no sense. There is always a give and take. The lower compression piston has less piston hight, taking up less space in the cylinder, giving you a higher displacement. The higher compression piston, means increased piston hight taking up more space of the cylinder, and decreasing displacement. Using his example of a 2L 4 cylinder, with a 500cc cylinder. The piston that gives you a low 8:1 compression, has a un-swept of 55cc. Giving you a total of 555cc, that is a 11% increase to displacement, that is a big deal. Bringing the true or total displacement of the engine to 2220cc or 2.2L. Now if you swap the pistons for a 14:1, I think he said you would have a un-swept of 35cc. Bringing the cylinder to a 535cc, and a total displacement of 2140cc, or a 2.1L. He also claimed a increase of 14hp, and a better fuel millage. Now he claimed that increasing compression decreases volume efficiency. From the data he has provided, that statement is false. How can a engine that has less displacement, and uses less fuel be said to have a lower volume efficiency? This is only possible when you have a increase of volume efficiency. We have to remember that all parts have to work together. For example increasing the flow rate of the head, on paper should mean more power, but in reality that might not be the case. A evo8 with the stock turbo would not see a increase in performance, it might actually decrease it, do to a decrease of air velocity or VE. The stock turbo does not flow enough air to support this. Now if you put a gt35 on it, then increasing the head flow rate makes sense and more power. I just want to say thank you for making this video, and sharing your knowledge.
Can you post the charts for compression ratio thermic efficiency and volumetric efficiency? Does this mean there is a point where the amount of boost would dictate your compression ratio?
3 things determine displacement bore. stroke. # of cylinders. Higher ignition temps depends on octane/fuel. 94 octane gas burns cooler than 87, E85 is cooler yet. Also, there's no way a 8:1 engine will have a higher VE than a 12:1 engine with all things being equal. Another thing 8:1 engine @ 45 psi you certainly won't be running 45 psi on a 12:1. 15 psi on a 12.1 will be making equal to or greater horsepower than 45 psi @ 8:1, plus the VE & efficiency on the 8:1 when not on boost is going to be terrible. Now if you talking NA, compression ratio is KING DADDY, there's no compromise, and the VE on high compression will always be greater than lower CR's. Good thing some of the top racers don't subscribe to your theory haha. I could go on but I'm tired of typing.
8:1 engine allows the possibility of filling more total volume than a 12:1 engine as the unswept volume is higher. Lower compression ratio engines always allow the possibility for higher VE.
I have a question. I have a supercharged 9.0:1 vvt 4.4 with 12 psi of boost with centrifugal blower and intercooler the size of the radiator. if I went with a 10. 5 4.8 with all things being equal from engine to engine minus comp ratio an displacement would I loose or win. I understand it a very general question.
So does this all mean for any given engine, if I had say 16 degrees at 47psi, 8000rpm with 9.0 comp and then raised the comp to say 9.7 with everything else remaining the same, there is a much higher chance of knock and detonation and cylinder pressure?
Yes, with everything else remaining the same. However, the combustion quality of the engine also plays a role. For example, using a thick head gasket to drop compression ratio often decreases the combustion efficiency of the engine. This can make a 9.0:1 CR engine with a thick head gasket that delivers a 0.080" piston to quench pad clearance more prone to detonation than a 9.7:1CR engine with a more ideal 0.040" piston to quench pad clearance. The tighter clearance increases turbulence and mixing making the air/fuel mixture less prone to detonation.
Racing engines have a way greater VE than 100%. Cylinders at rpm are being filled with more volume than the math indicates. Due to valve events, and port velocity. Design of quench area is extremely important when building a engine that runs better than it should. A 8 to 1 engine will spark knock way more than a 10 to 1 engine. The efficiency of the combustion chamber is more important than CR within reason. 9:1 vs 12:1. All my experience comes from NA Racing. I know very little about boosted apps.
great work Michael! Very smooth delivery of technical stuff. Just a quick question: why does total volume increase with increasing compression ratios? I mean why not just decrease unswept volume like you showed in the Subaru heads example and increase swept volume to accordingly account for that decrease keeping total the same? or is is some kind of standard volume values manufacturers follow? Thanks!
The swept volume of an engine is only a function of bore and stroke. It won't change unless a change is made to bore or stroke. The unswept volume is dependent upon cylinder head volume, head gasket volume, piston dome/dish volume.
I'm reading between the lines here but if volumetric efficiency is the ratio of fuel/air charge volume to swept cylinder volume then presumably the reason a higher compression ratio yields worse efficiency, is that you have to ease off the volume of gas introduced into the cylinder on each stroke, so as to avoid preignition, right? Because at high compression, knocking is going to occur if you cram too much gas in there.
Not exactly. Your definition of VE is pretty much on point. If you have a 500cc displacement cylinder but you are able to fill the cylinder and combustion chamber with 550cc of air/fuel mixture (10% more than the swept volume) you would have an engine with 10%+100% or 110% volumetric efficiency. Compression ration is the ratio of the swept+unswept volume to the unswept volume. This represents the volume ratio change to the intake charge as the piston moves from bottom dead center to top dead center on the compression stroke. As this volume ratio increases, in cylinder temperatures also increase and the likelihood for autoignition increase.
Great class good nowlege can't off tricky or confused but I highet comp lest boost more power that's my understanding great 👍 video man but very derispect full people in there
Compression ratio does not affect volumetric efficiency -- volumetric efficiency is just how much air mass a cylinder actually sucks in vs. how much air mass the cylinder can "maximally" hold (as if the piston did nothing and just sat with open valves at BDC all day). The slower the piston (giving more time for air to flow in) and the bigger the valves (for more air inflow "area"), the better the volumetric efficiency. Simple as that -- compression ratio plays no role.
He is right, increasing the compression ratio, decreases the volumetric efficiency, because it actually changes the total usable volume of the engine, thus, even if the VE as a % does not change by much, or it's insignificant, the actual torque decreases. He is not considering the actual flow of the engine, but the absolute volume and only when the change is major, from 8:1 to 14:1, or something like that. In the end, it's better to have more air compressed less, than less air compressed more...
@TheSilviu Not quite -- you should reread the definition of volumetric efficiency again. And if you reply please repeat the definition of VE in your post too so that I know if you actually understand what VE is or not. It has zero to do with actual engine volume or compression ratio. And technically all of the "volume" of a cylinder is both usable and is used, for your information, as there's no "perfect vacuum" anywhere in an engine.
@@MikeSmith-vb8ul Compression ratio can absolutely effect volumetric efficiency, both positively and negatively. It depends on how volumetrically efficient the engine is. An engine with a very high volumetric efficiency. Let's say 130% of theoretical maximum volume (obviously a high boost motor), would lose VE because the higher compression would come from a reduction in the theoretical maximum volume, therefore also taking away from the actual air volume it's seeing. The turbo is forcing air into the engine, when it's doing a lot of that, and you take away volume from the space it's trying to fill, it can't fill as much, and the higher boost your running, the worse that effect is. If you remove 1 CC of swept volume, what had more air in that CC, the volume at 15psi or 30? By reducing the theoretical maximum volume on an engine with over 100% VE, your cheating it out of potential air, because it can fill that volume at over 100% efficiency. Now of course thermal efficiency matters too, but just like static compression. Raising effective compression from boost also raises thermal efficiency. That's why a low compression high boost motor makes more power than a high compression low boost motor, It can have the highest VE AND the highest thermal efficiency. Now I did say that raising compression can also raise VE, and it can, but not to the same degree, and only engine with low volumetric efficiency, a reduction in the theoretical maximum volume in the form of a bump in compression, can actually raise volumetric efficiency if the engine wasn't filling it's theoretical maximum volume efficiently in the first place. Does that make sense?
I have a question, what about NA engines with no turbo/boost? Does high comp ratio equal more power in NA's? When would it be advisable to increase CR in a NA engine?
Thank You for sharing! I love all motor application, and this is definitely worth watching and learning! By the way, I was basing the 2L bore and stroke off from a factory K20 86x86. It’s easier for me to compared and reference. Love it! #allmotor
A lot of math,, but all is lost as you forget one thing. The higher unswept volume the more possibilites to have more diluted gasses left in cylinder when exhaustvalve closes. Especially in turboengines that reaches equal exhaustpressure as boost, or even worse, higher exhaustpressure than boostpressure. This combo won´t 'flush' the combustionchamber as good as an tuned N/A engine. One might think that pulsation would take care of that, and yes in an N/A engine it can do that, and reach high VE numbers. But a turboengine is something else. It can have some pulsation left, but as the pressurelevels over intake/exhaust during overlap is higher in boosted mode, the density is higher, tempratures is higher, so all pulsetuning in N/A mode alters quickly and might even become really bad. The experienced guy will recognize this that the N/A engine with a tuned header might have some 'chop' to the idle. And when slapping that turbo exhaust manifold on it the idle chop increases.
You didn’t explain WHY you get less power with more boost and higher comp ratio. Is it to do with knock limitation??... or are you still able to reach MBT??
Would this be the same for the FA20DIT application? Also have you guys seen any actual fa20dit with built engine's last more then 20k miles? I'm starting to believe the 15+wrx should not be built
All these numbers are peak HP? What about area under the curve. I've built a 10:1 RB25, all angled to mid range. Peak boost will be 28-30PSI. So what affect do you have in the mid range...
@@dsport But HP and torque is engine speed dependant. I' m Aware HP is a factor of torque and engine speed, have the formula somewhere. But as you said, higher cylinder pressure = higher torque.
@@tangles01 Nothing to do with engine speed. Compared to running at a 8:0 compression ratio, you will have more power off boost and when you stay under 18 psi of boost. At zero boost, you'll be making 3.6% more power thanks to the higher compression ratio. When you are at 15psi of boost, you'll be making 0.8-percent more power. Once you go over 19spi of boost, you'll be making less power than the lower compression ratio. At 30psi, you'll be down 2.0-percent in power versus what you would have been making if you kept the engine at 8.0:1. If you are making 600whp with the 10:1 setup, you would have made 612whp with the 8.0:1 setup at 30psi of boost.
@@dsport I'm not disagreeing with your math on the percentages or the on/off boost part. lets say it is 600 at 30psi it will be for round numbers sake 8000rpm, being an RB. I concede it will have been 612 or so at peak power. But I have 30psi at 4000rpm too. And we both know it's not making 600hp there (I haven't run it in just yest,so actual dyno numbers are TBA). My question is how is the torque affected then. Are your factors only a factor of peak HP or are they a linear deficient all the way though the power range? Or don't you know, which is a fine answer, most people don't worry about anything apart from the top number and for drag application and bragging rights, that the important one, for circuit racing however the mid range is critical for me.
Great video. it helped me a lot. I have one question if u don't mind. I have a car with a 4 cylinder 1.747 L engine that produces 130hp and a compression ratio of 12.1:1(multiport injection) and a weight of 1222 Kg or 2696 pounds. Let's say I want to achieve 200 250 hp, If put a turbo should I lower the compression? or can I get away with the same compression and not so much boost? what would you consider ideal and what would be ok to do? looking for a fun "reliable" build
12.1 comp is, in general, too high for boost on a stock motor. If anything, you'll want something more like 9-10 comp on low boost and preferably on e85.
Have you posted the Math or charts to calculate this. I am at 11:1, VQ37VHR at 22psi of boost. HP was 780whp. Factory compression was 11:1. I am trying to figure out what compression ratio I need to run. I am building another engine. Max boost will be 24psi this time.
You are very close to the tipping point. You would have a slight gain going down in compression ratio at that boost pressure level. However when the engine is at lower boost levels or no boost at all it will be slightly less efficient. So you should be OK with anything besides going up in compression ratio.
Honda engines.... I got a JDM F20B (11:0.1 Stock Compression). Thinking of fully building this engine & going 12:0.1 on 10psi max. How reliable so you think that will be? Honestly just making this build to daily the car & keep up with modern daily sports cars. I went from a D15B8 (70 HP) to F20B (200HP). Not building an all out racecar just want something fast & fun to abuse daily. Most likely going to keep it at 5 or 7psi since I don't want to blow the engine & lose all my $$. Reason why I say 12:1 Compression is because it's almost the same Compression as stock. I won't dare to go 13 or 14:1.
ok then can I ask something so what different compression 10:1 and 9:1 if they dynamic compression is same like 8:1 dynamic compreession?? what different in power and thermal efficiency between that 2 static compression ratio????
The best way to think about the effects of compression ratio is to understand that all other factors being equal, an increase in static compression ratio will increase the thermal efficiency of the engine and reduce the volumetric efficiency of the engine. For any engine, a change in the cylinder filling will change the engine's dynamic compression ratio. If you change the cams, modify the intake and port the cylinder head, the dynamic compression ratio can change. For your example, the engine with the higher static compression ratio will still have a higher thermal efficiency even if both engines share a similar dynamic compression ratio. Remember that most engines have identical compression ratios to expansion ratios. Even if the different camshafts affect the dynamic compression ratio, the expansion ratio of a 10:1 engine allows over 10% more volume for expansion that a 9:1 engine. Increasing the expansion ratio allows for more of the engine to be used for work instead being shifted off to waste (exhaust heat, cooling system, oil, etc.).
Nice work Dsport. But if you extrapolate the maths to even lower compression ratios then the numbers show significant total gains by going even lower than 8. Have you done the maths for a compression of 5 or 6? This show 10-20 percent gains on some engines in theory.
One of the most fun engines I ever built had 6.5:1 compression and ran close to 40 degrees of timing and around 15 psi of boost, and ran on 92 octane. Carbed and old school draw through turbo... it "felt" like a NA car with a really high compression ratio and sick SNAP throttle response and boost response.... Don't be afraid to experiment.
How big a turbo.....and then how much boost on that big turbo? I'm assuming if you watched the video you have a pretty good idea on how it will turn out.
You must be new at this. The engine is a combination of parts that must work together, hence a given compression ratio must be combined with the right cam and heads to max it out.
Very nice vid ive been building engines for a long time lol I just stuck to what worked but have a better understanding now I can picture it in my head what is happening thanks loads
For piston-ported 2-strokes (chainsaws), does this "volumetric efficiency" concept matter? I've watched your (awesome!!) presentation a couple times now and still struggling to understand this "losing volumetric efficiency" concept, when explained it basically sounds like "If you have a smaller combustion-chamber, you 'lose' volumetric efficiency" -- well, of course, that is inherent it's like using synonyms, to reduce the chamber and up compression is to inherently reduce chamber-size (though I'm still lost on the concept of 'volumetric efficiency' as, to my misunderstanding ears, it sounds like wishful thinking "Oh if only we had the larger combustion-volume *and* the higher compression" (ie have your cake & eat it, too) which of course doesn't happen....this "volumetric efficiency" concept sounds like it is automatically "inverse-correlate" to compression-level of the jug, so the idea of "efficiency" being part of the term confuses me (ie why not just say 'reduces area of combustion', yknow?) For chainsaws where boost is not on the table, and compression is kinda "the go-to" for higher-power modifications of saws, it has me wondering again if "more=better" for this application (IE, it's "more-better" at least until the point you're snapping rods / cracking pistons / etc) For context, I'm working on a pair of kit saws that are 92cc displacement, OEM spec is 13.1:1 compression ratio but I took the cylinder and squish band down so the entire jug sits lower on the crankcase *and*, with that higher squish band, my combustion-dome is now automatically smaller....problem is I'm having a helluva time telling what "ideal" compression would be here, I can really only aim at it as I've also ported the case (ie volume is now >92cc) but it keeps seeming like "I should go more & more compression until I'm worrying about the rod / internal failure of engine components", it doesn't seem like there's a practical wall to performance IE *if* I had titanium internals that could take 15:1, that *would* mean a stronger saw, period. Thanks again for the video & even more if you can help me out, have watched all the chainsaw-specific content that seemed worthy but so much misses so many critical concepts (it's a norm to take a 1/2" drill to the rear of the muffler "for flow & cooling" w/o a 2nd thought Re negating the back-pressure required of a muffler for a 2-stroke to function properly :P )
Pretty open ended question with too many variables. It's the law of diminishing returns, at some point the cost in race gas, ceramic combustion chamber coatings etc needed to run full timing with no knock will outweigh the .2% you'll gain from a full point compression increase but 16:1-17:1 isn't uncommon in piston engined race cars.
@@trixnhoez2964 I am already running the maximum factory setting of ignition advance on my Protege. Pause on the distributor part of my video if you want to? I have A prototype that reduces knock. It even works on diesel engines. Race gas is not needed, just 85 octane fuel will do the trick. Thanks, for your input on this subject!
32:25 I have a fa20 brz. So if I reprofile my combustion chamber and shave some of the of the material to mimic the fa20f combustion chamber, I can effectively lower my 12:5 compression ratio for boosted application?
@@lilmixdboy it's not that. It's more of getting to the same result with a different approach than the norm. ie shaved combustion chambers vs low comp piston swap.
Screw the science just drive a turbo trans am from 1980 with 8 to 1 and them drive a small block with 10 and a half to 1 flattop and the non turbo will roast the turbo car like it's a 4 cylinder 80 horse engine lol
I am hoping to build my k20 I want to turbo it at simi low boost What my goal is I want to increase my mileage and power my factory compression is 11.0 when i rebuild the engine I had planned to run 12.0 on 7-14 psi this is a normal street car and want reliability. I'm not chasing the drag strip mostly hoping to break end up with 300 ish hp and slightly better fuel mileage. would I be smarter to run 11.5:1, stock, or the 12.1 I had planned. the car will probably be out of boost most of the time and didn't want to give up the low end.
Linearburn these Honda engines are highly strung from factory. I wouldn’t dream of increasing comp ratio when adding boost to a already high comp engine. I doubt you’ll get to 14 psi on a 11:1 K20 with E85. You’ll probably reach MBT at like 11 psi.
i think you need to understand about level of combustion accure in different level of compression. i know when we increase compression ratio, it will degrease swept volume like you what you say. but its just make tiny different than increase compression. if compression increase, level of heat combustion will do. i am study in mechanical engineering. so i know about this.
It's about cylinder pressure not compression ratio. The bigger the cam in duration the more compression ratio your need to maintain a given cylinder pressure.
Before I view your video; I must emphasize an evident need of a multiple fuel types injecting systems of tweakings on an automatics management programing capabilities. And also; why isn't there a weighted type of piston or a ram system that cranks cocked a load that keeps a force or anything that makes more sense than top dead center being the combustion instead of the chamber being on a up down cycle as an also application where one's combustion is diverted as channeled within the last one before's chamber that it also had done the same(a need for 16 for 2 cycle and 32 pistons for a four cycle would be needed for this) ........... It takes such shallow concentrations in order to advance logistics of combustions engines; that I realised another while writing this. It's the chamber that needs to drive a crank driver; of or and an engine should be a drive motor.Cheers
@@isabellab617 I don't know if we are talking about the same truck/engine. Hardbobys were different trucks imported to Mexico from the USA. And it was a totally different trim than the panel mexican truck. Mexican Nissan panel trucks were made for heavy duty. Higher compression for fuel economy and short gear ratio specially 1st and 2nd for heavy loads. Engine were totally different than the one on the USA market Hardbobys. I owned both. And the brochure of the Mexican panel truck said near 11+ to 1 comp ratio. I just square it to 12. It doesn't said what engine series was but is all I remember. Plus I'm not going to argue about it. We use to load these trucks with 2+ tons. And not problem moving that weight on my town hills... Or around los Altos de Jalisco... Hardbobys where faster but not stronger with heavy loads. And also my street truck was a 76 gmc high Sierra 4x4 that I swapped in a 700r4 MD8 and a rare 327 4 main bolts engine. Now tell me " these 327 with 4 main bolts on the crankshaft doesn't exist".. Yes they do exist. I owned one.. It was a from a late 60's corvette. But that's Arina de different costal. I was racing 1/4 of mile on 4x4 in 1996. Now is the trend in the USA 😂😂😂😂😂
Would have been better if you went threw the maths how you found the loss in power on high boost etc You could be chatting crap lol but good content thanks again
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This classroom is dope, I wish I had this in school back in the days...
Thank you!
Only 41k views? This video is so under rated and full of useful information. Thank you Dsport, for taking the time to nourish us car geeks with this information
Blame it on the algorithms!! LOL
Great presentation. Very well spoken. DSPORT deserves an award who agrees?
This was absolutely fantastic!! And free!! Are you for real!! I feel like I waisted thousands of dollars in education after this. Thank you so much!!
D-Sport has been doin' the Lords' work!
😂 🙏 Hallelujah 🙏 😂
Thank you Tommy.
Truth🤘
Love the way you explain everything, goes straight to the brain. I wish, i could've got to attend your classes/workshop.
Higher compression in boosted applications definitely has its place more compression means you can make the same power with less boost and get faster spoil I think That's why things are really going that direction nowadays
This is why I'm watching this video im going from 8.2 to 9.0 boosted application
cummins 855 turbo diesels lower the compression to gain hp
@@ccclc6159 Diesel cycle has different thermodynamics and different combustion process(Heterogeneous). He is talking about compression ratio in otto cycle(Petrol) engines.
@@metaphorpritamhey dingdong did I mention diesel? he says pump gas and e85 in the first 30seconds, early farm tractors usually came with gasoline or propane engines, propane tractors had higher compression pistons installed so they would make about the same hp as the gas version, btw what is a diesel cycle? do you think there is a gas vs diesel cycle?
@@ccclc6159 Yes mr. Chutiya....you did mention Cummins 855 turbo diesel
XR650L - 2009 version. 8.3 going to 10.2 on local pump gas 95 Octane - should be a sweet spot. Smoking hopium until things turn out right. Cool channel. Greetings from DBN.
I raised my fiesta's compression to 12 to 1 and over bored it .75 and I can feel the difference. It was part of the Rebuild
I’m only 8 min in and I’ve already learned a ton. Cheers mate
Great video !!! You really didn’t addressed noc psi or NA engines or the math behind it, however this was awesome I think if you added a tiny bit of animated grafix and charts we would all understand allot better
As the unswept volume decreases with increasing CR , swept volume increases as well .. total volume remains constant . At 9:13/9:42 you call 2nd column unswept , later 10:19 calling it swept !!!
Yeah. That confused me too.
That is not correct. You have two segments that need to be looked at separately. The swept volume is only the distance between the piston top and the edge of the block when the piston is at BDC. The chamber volume (unswept) is a separate thing and when you change that volume, the swept volume doesn't change. But when you look at the combination of both (total volume) and you reduce the chamber volume to increase CR, the total volume decreases by the amount the chamber volume was reduced. Has no effect on the swept volume portion though.
The definition for engine displacement is flawed. Bore and stroke is not the total volume or displacement of a engine. To exclude the piston hight, the un-swept, or (combustion chamber), makes no sense.
There is always a give and take. The lower compression piston has less piston hight, taking up less space in the cylinder, giving you a higher displacement. The higher compression piston, means increased piston hight taking up more space of the cylinder, and decreasing displacement.
Using his example of a 2L 4 cylinder, with a 500cc cylinder. The piston that gives you a low 8:1 compression, has a un-swept of 55cc. Giving you a total of 555cc, that is a 11% increase to displacement, that is a big deal. Bringing the true or total displacement of the engine to 2220cc or 2.2L.
Now if you swap the pistons for a 14:1, I think he said you would have a un-swept of 35cc. Bringing the cylinder to a 535cc, and a total displacement of 2140cc, or a 2.1L. He also claimed a increase of 14hp, and a better fuel millage.
Now he claimed that increasing compression decreases volume efficiency. From the data he has provided, that statement is false. How can a engine that has less displacement, and uses less fuel be said to have a lower volume efficiency? This is only possible when you have a increase of volume efficiency.
We have to remember that all parts have to work together. For example increasing the flow rate of the head, on paper should mean more power, but in reality that might not be the case. A evo8 with the stock turbo would not see a increase in performance, it might actually decrease it, do to a decrease of air velocity or VE. The stock turbo does not flow enough air to support this. Now if you put a gt35 on it, then increasing the head flow rate makes sense and more power.
I just want to say thank you for making this video, and sharing your knowledge.
Can you post the charts for compression ratio thermic efficiency and volumetric efficiency? Does this mean there is a point where the amount of boost would dictate your compression ratio?
3 things determine displacement bore. stroke. # of cylinders. Higher ignition temps depends on octane/fuel. 94 octane gas burns cooler than 87, E85 is cooler yet. Also, there's no way a 8:1 engine will have a higher VE than a 12:1 engine with all things being equal. Another thing 8:1 engine @ 45 psi you certainly won't be running 45 psi on a 12:1. 15 psi on a 12.1 will be making equal to or greater horsepower than 45 psi @ 8:1, plus the VE & efficiency on the 8:1 when not on boost is going to be terrible. Now if you talking NA, compression ratio is KING DADDY, there's no compromise, and the VE on high compression will always be greater than lower CR's. Good thing some of the top racers don't subscribe to your theory haha. I could go on but I'm tired of typing.
nice reply by someone that knows his stuff wild
The drinking of too much RedBull, lead to nervousness, lack of concentration, patience and preciseness :)
he is incorrect@@vinlemarechal8296
8:1 engine allows the possibility of filling more total volume than a 12:1 engine as the unswept volume is higher. Lower compression ratio engines always allow the possibility for higher VE.
I have a question. I have a supercharged 9.0:1 vvt 4.4 with 12 psi of boost with centrifugal blower and intercooler the size of the radiator. if I went with a 10. 5 4.8 with all things being equal from engine to engine minus comp ratio an displacement would I loose or win. I understand it a very general question.
How do I determine the proper timing for a engine that is being built as a high compression engine?
What would the cross over point be on a port injection motor as we run much lower cr as opposed to direct injection
So does this all mean for any given engine, if I had say 16 degrees at 47psi, 8000rpm with 9.0 comp and then raised the comp to say 9.7 with everything else remaining the same, there is a much higher chance of knock and detonation and cylinder pressure?
Yes, with everything else remaining the same. However, the combustion quality of the engine also plays a role. For example, using a thick head gasket to drop compression ratio often decreases the combustion efficiency of the engine. This can make a 9.0:1 CR engine with a thick head gasket that delivers a 0.080" piston to quench pad clearance more prone to detonation than a 9.7:1CR engine with a more ideal 0.040" piston to quench pad clearance. The tighter clearance increases turbulence and mixing making the air/fuel mixture less prone to detonation.
Racing engines have a way greater VE than 100%. Cylinders at rpm are being filled with more volume than the math indicates. Due to valve events, and port velocity. Design of quench area is extremely important when building a engine that runs better than it should.
A 8 to 1 engine will spark knock way more than a 10 to 1 engine.
The efficiency of the combustion chamber is more important than CR within reason. 9:1 vs 12:1.
All my experience comes from NA Racing.
I know very little about boosted apps.
Very true. Always seek to make no decrease to combustion efficiency when changing the compression ratio,
Which one is good for fuel economy?
great work Michael! Very smooth delivery of technical stuff. Just a quick question: why does total volume increase with increasing compression ratios? I mean why not just decrease unswept volume like you showed in the Subaru heads example and increase swept volume to accordingly account for that decrease keeping total the same? or is is some kind of standard volume values manufacturers follow? Thanks!
The swept volume of an engine is only a function of bore and stroke. It won't change unless a change is made to bore or stroke.
The unswept volume is dependent upon cylinder head volume, head gasket volume, piston dome/dish volume.
I'm reading between the lines here but if volumetric efficiency is the ratio of fuel/air charge volume to swept cylinder volume then presumably the reason a higher compression ratio yields worse efficiency, is that you have to ease off the volume of gas introduced into the cylinder on each stroke, so as to avoid preignition, right? Because at high compression, knocking is going to occur if you cram too much gas in there.
Not exactly. Your definition of VE is pretty much on point. If you have a 500cc displacement cylinder but you are able to fill the cylinder and combustion chamber with 550cc of air/fuel mixture (10% more than the swept volume) you would have an engine with 10%+100% or 110% volumetric efficiency.
Compression ration is the ratio of the swept+unswept volume to the unswept volume. This represents the volume ratio change to the intake charge as the piston moves from bottom dead center to top dead center on the compression stroke. As this volume ratio increases, in cylinder temperatures also increase and the likelihood for autoignition increase.
Great class good nowlege can't off tricky or confused but I highet comp lest boost more power that's my understanding great 👍 video man but very derispect full people in there
Compression ratio does not affect volumetric efficiency -- volumetric efficiency is just how much air mass a cylinder actually sucks in vs. how much air mass the cylinder can "maximally" hold (as if the piston did nothing and just sat with open valves at BDC all day). The slower the piston (giving more time for air to flow in) and the bigger the valves (for more air inflow "area"), the better the volumetric efficiency. Simple as that -- compression ratio plays no role.
Agreed...
He is right, increasing the compression ratio, decreases the volumetric efficiency, because it actually changes the total usable volume of the engine, thus, even if the VE as a % does not change by much, or it's insignificant, the actual torque decreases.
He is not considering the actual flow of the engine, but the absolute volume and only when the change is major, from 8:1 to 14:1, or something like that.
In the end, it's better to have more air compressed less, than less air compressed more...
@TheSilviu Not quite -- you should reread the definition of volumetric efficiency again. And if you reply please repeat the definition of VE in your post too so that I know if you actually understand what VE is or not. It has zero to do with actual engine volume or compression ratio. And technically all of the "volume" of a cylinder is both usable and is used, for your information, as there's no "perfect vacuum" anywhere in an engine.
@@MikeSmith-vb8ul Compression ratio can absolutely effect volumetric efficiency, both positively and negatively. It depends on how volumetrically efficient the engine is. An engine with a very high volumetric efficiency. Let's say 130% of theoretical maximum volume (obviously a high boost motor), would lose VE because the higher compression would come from a reduction in the theoretical maximum volume, therefore also taking away from the actual air volume it's seeing. The turbo is forcing air into the engine, when it's doing a lot of that, and you take away volume from the space it's trying to fill, it can't fill as much, and the higher boost your running, the worse that effect is. If you remove 1 CC of swept volume, what had more air in that CC, the volume at 15psi or 30? By reducing the theoretical maximum volume on an engine with over 100% VE, your cheating it out of potential air, because it can fill that volume at over 100% efficiency. Now of course thermal efficiency matters too, but just like static compression. Raising effective compression from boost also raises thermal efficiency. That's why a low compression high boost motor makes more power than a high compression low boost motor, It can have the highest VE AND the highest thermal efficiency. Now I did say that raising compression can also raise VE, and it can, but not to the same degree, and only engine with low volumetric efficiency, a reduction in the theoretical maximum volume in the form of a bump in compression, can actually raise volumetric efficiency if the engine wasn't filling it's theoretical maximum volume efficiently in the first place. Does that make sense?
I have a question, what about NA engines with no turbo/boost? Does high comp ratio equal more power in NA's? When would it be advisable to increase CR in a NA engine?
In general yes. Of course you will be limited by fuel octane quality.
what about non turbocharged engines? like bike engines , what if it is changed from 9:1 to 12:1?
Thank You for sharing! I love all motor application, and this is definitely worth watching and learning!
By the way, I was basing the 2L bore and stroke off from a factory K20 86x86. It’s easier for me to compared and reference.
Love it!
#allmotor
Very interesting and informative.
A lot of math,, but all is lost as you forget one thing.
The higher unswept volume the more possibilites to have more diluted gasses left in cylinder when exhaustvalve closes.
Especially in turboengines that reaches equal exhaustpressure as boost, or even worse, higher exhaustpressure than boostpressure.
This combo won´t 'flush' the combustionchamber as good as an tuned N/A engine.
One might think that pulsation would take care of that, and yes in an N/A engine it can do that, and reach high VE numbers.
But a turboengine is something else.
It can have some pulsation left, but as the pressurelevels over intake/exhaust during overlap is higher in boosted mode, the density is higher, tempratures is higher, so all pulsetuning in N/A mode alters quickly and might even become really bad.
The experienced guy will recognize this that the N/A engine with a tuned header might have some 'chop' to the idle.
And when slapping that turbo exhaust manifold on it the idle chop increases.
Thus enters VVT and L to help balance chamber temp and there by helping change high and low pressure
You didn’t explain WHY you get less power with more boost and higher comp ratio.
Is it to do with knock limitation??... or are you still able to reach MBT??
He did explain it because....because there is less compressed volume to go "BOOM"
Less air which means less fuel = less power.
All that and miss the real point. Compression ratio is really the EXPANSION RATIO.
Would this be the same for the FA20DIT application? Also have you guys seen any actual fa20dit with built engine's last more then 20k miles? I'm starting to believe the 15+wrx should not be built
All these numbers are peak HP? What about area under the curve. I've built a 10:1 RB25, all angled to mid range. Peak boost will be 28-30PSI. So what affect do you have in the mid range...
Good question. Changing the compression ratio are not engine speed dependent at all. It only affects power on-boost and off-boost.
@@dsport But HP and torque is engine speed dependant. I' m Aware HP is a factor of torque and engine speed, have the formula somewhere. But as you said, higher cylinder pressure = higher torque.
@@tangles01 Nothing to do with engine speed. Compared to running at a 8:0 compression ratio, you will have more power off boost and when you stay under 18 psi of boost. At zero boost, you'll be making 3.6% more power thanks to the higher compression ratio. When you are at 15psi of boost, you'll be making 0.8-percent more power. Once you go over 19spi of boost, you'll be making less power than the lower compression ratio. At 30psi, you'll be down 2.0-percent in power versus what you would have been making if you kept the engine at 8.0:1. If you are making 600whp with the 10:1 setup, you would have made 612whp with the 8.0:1 setup at 30psi of boost.
@@dsport I'm not disagreeing with your math on the percentages or the on/off boost part. lets say it is 600 at 30psi it will be for round numbers sake 8000rpm, being an RB. I concede it will have been 612 or so at peak power. But I have 30psi at 4000rpm too. And we both know it's not making 600hp there (I haven't run it in just yest,so actual dyno numbers are TBA). My question is how is the torque affected then. Are your factors only a factor of peak HP or are they a linear deficient all the way though the power range? Or don't you know, which is a fine answer, most people don't worry about anything apart from the top number and for drag application and bragging rights, that the important one, for circuit racing however the mid range is critical for me.
So if increase the compression at top dead center(high comp piston) whats the technical terms ?
What compression ratio can I use in my all motor h22a,5100139 want more power
Great video. it helped me a lot.
I have one question if u don't mind. I have a car with a 4 cylinder 1.747 L engine that produces 130hp and a compression ratio of 12.1:1(multiport injection) and a weight of 1222 Kg or 2696 pounds. Let's say I want to achieve 200 250 hp, If put a turbo should I lower the compression? or can I get away with the same compression and not so much boost? what would you consider ideal and what would be ok to do? looking for a fun "reliable" build
The answer to your question is yes and no
12.1 comp is, in general, too high for boost on a stock motor. If anything, you'll want something more like 9-10 comp on low boost and preferably on e85.
Have you posted the Math or charts to calculate this. I am at 11:1, VQ37VHR at 22psi of boost. HP was 780whp. Factory compression was 11:1. I am trying to figure out what compression ratio I need to run. I am building another engine. Max boost will be 24psi this time.
You are very close to the tipping point. You would have a slight gain going down in compression ratio at that boost pressure level. However when the engine is at lower boost levels or no boost at all it will be slightly less efficient. So you should be OK with anything besides going up in compression ratio.
@@dsport I dropped down to 10:1 and turned up the boost a little more. My off boost performance is still good.
Honda engines....
I got a JDM F20B (11:0.1 Stock Compression). Thinking of fully building this engine & going 12:0.1 on 10psi max. How reliable so you think that will be?
Honestly just making this build to daily the car & keep up with modern daily sports cars. I went from a D15B8 (70 HP) to F20B (200HP).
Not building an all out racecar just want something fast & fun to abuse daily. Most likely going to keep it at 5 or 7psi since I don't want to blow the engine & lose all my $$.
Reason why I say 12:1 Compression is because it's almost the same Compression as stock. I won't dare to go 13 or 14:1.
EG_ VATO and what kind of fuel are you expecting to run??
When the teacher is teaching whith he’s heart and you got kids in the class room
very good sir, ty ty
ok then can I ask something
so what different compression 10:1 and 9:1 if they dynamic compression is same like 8:1 dynamic compreession??
what different in power and thermal efficiency between that 2 static compression ratio????
The best way to think about the effects of compression ratio is to understand that all other factors being equal, an increase in static compression ratio will increase the thermal efficiency of the engine and reduce the volumetric efficiency of the engine.
For any engine, a change in the cylinder filling will change the engine's dynamic compression ratio. If you change the cams, modify the intake and port the cylinder head, the dynamic compression ratio can change.
For your example, the engine with the higher static compression ratio will still have a higher thermal efficiency even if both engines share a similar dynamic compression ratio. Remember that most engines have identical compression ratios to expansion ratios. Even if the different camshafts affect the dynamic compression ratio, the expansion ratio of a 10:1 engine allows over 10% more volume for expansion that a 9:1 engine. Increasing the expansion ratio allows for more of the engine to be used for work instead being shifted off to waste (exhaust heat, cooling system, oil, etc.).
@DSPORT so i have a built Fa20 at 10:1 compression but with wrx pistons running about 20psi... can you explain what is going on in my chambers?
Easy, reduce your compression ratio to increase boost and actually gain herseper. Lol
Nice work Dsport. But if you extrapolate the maths to even lower compression ratios then the numbers show significant total gains by going even lower than 8. Have you done the maths for a compression of 5 or 6? This show 10-20 percent gains on some engines in theory.
One of the most fun engines I ever built had 6.5:1 compression and ran close to 40 degrees of timing and around 15 psi of boost, and ran on 92 octane. Carbed and old school draw through turbo... it "felt" like a NA car with a really high compression ratio and sick SNAP throttle response and boost response.... Don't be afraid to experiment.
Running a 13:1 big turbo on my built lsvt hoping to see how it runs
Kc Konuk it’ll run until you put your foot down... and then it won’t run... until you replace the block, pistons and rods.
@@mareksumguy1887 I miss typed that I'm running 12:1
Kc Konuk you have a lot of learning to do.
How big a turbo.....and then how much boost on that big turbo? I'm assuming if you watched the video you have a pretty good idea on how it will turn out.
An L shall be handed out when you go past 5500 rpm or so
You must be new at this. The engine is a combination of parts that must work together, hence a given compression ratio must be combined with the right cam and heads to max it out.
Very nice vid ive been building engines for a long time lol I just stuck to what worked but have a better understanding now I can picture it in my head what is happening thanks loads
farm tractors used to have low compression pistons to run on gasoline and high compression pistons to run on propane
Thank you sir,big help to me👍
Do the math using the imperial system. I dear you. Lol Nice vid.
so you telling me at lower boost levels a 250 could be improved?
For piston-ported 2-strokes (chainsaws), does this "volumetric efficiency" concept matter? I've watched your (awesome!!) presentation a couple times now and still struggling to understand this "losing volumetric efficiency" concept, when explained it basically sounds like "If you have a smaller combustion-chamber, you 'lose' volumetric efficiency" -- well, of course, that is inherent it's like using synonyms, to reduce the chamber and up compression is to inherently reduce chamber-size (though I'm still lost on the concept of 'volumetric efficiency' as, to my misunderstanding ears, it sounds like wishful thinking "Oh if only we had the larger combustion-volume *and* the higher compression" (ie have your cake & eat it, too) which of course doesn't happen....this "volumetric efficiency" concept sounds like it is automatically "inverse-correlate" to compression-level of the jug, so the idea of "efficiency" being part of the term confuses me (ie why not just say 'reduces area of combustion', yknow?)
For chainsaws where boost is not on the table, and compression is kinda "the go-to" for higher-power modifications of saws, it has me wondering again if "more=better" for this application (IE, it's "more-better" at least until the point you're snapping rods / cracking pistons / etc)
For context, I'm working on a pair of kit saws that are 92cc displacement, OEM spec is 13.1:1 compression ratio but I took the cylinder and squish band down so the entire jug sits lower on the crankcase *and*, with that higher squish band, my combustion-dome is now automatically smaller....problem is I'm having a helluva time telling what "ideal" compression would be here, I can really only aim at it as I've also ported the case (ie volume is now >92cc) but it keeps seeming like "I should go more & more compression until I'm worrying about the rod / internal failure of engine components", it doesn't seem like there's a practical wall to performance IE *if* I had titanium internals that could take 15:1, that *would* mean a stronger saw, period.
Thanks again for the video & even more if you can help me out, have watched all the chainsaw-specific content that seemed worthy but so much misses so many critical concepts (it's a norm to take a 1/2" drill to the rear of the muffler "for flow & cooling" w/o a 2nd thought Re negating the back-pressure required of a muffler for a 2-stroke to function properly :P )
What's the highest compression
ratio you would want to run on A NA build, if knock was not A factor?
Pretty open ended question with too many variables. It's the law of diminishing returns, at some point the cost in race gas, ceramic combustion chamber coatings etc needed to run full timing with no knock will outweigh the .2% you'll gain from a full point compression increase but 16:1-17:1 isn't uncommon in piston engined race cars.
@@trixnhoez2964 I am already running the maximum factory setting of ignition advance on my Protege.
Pause on the distributor part of my video if you want to?
I have A prototype that reduces knock. It even works on diesel engines.
Race gas is not needed, just 85 octane fuel will do the trick.
Thanks, for your input on this subject!
This was an awesome video. Thank you so much for making this
Thank you so much for watching.
I appreciate the video.
Thank you.
32:25 I have a fa20 brz. So if I reprofile my combustion chamber and shave some of the of the material to mimic the fa20f combustion chamber, I can effectively lower my 12:5 compression ratio for boosted application?
You cant buy new pistons?
@@lilmixdboy it's not that. It's more of getting to the same result with a different approach than the norm. ie shaved combustion chambers vs low comp piston swap.
Screw the science just drive a turbo trans am from 1980 with 8 to 1 and them drive a small block with 10 and a half to 1 flattop and the non turbo will roast the turbo car like it's a 4 cylinder 80 horse engine lol
Bore x bore x stroke x .7854 x number of cylinders🚀
You left the labels on the small containers...
I am hoping to build my k20 I want to turbo it at simi low boost What my goal is I want to increase my mileage and power my factory compression is 11.0 when i rebuild the engine I had planned to run 12.0 on 7-14 psi this is a normal street car and want reliability. I'm not chasing the drag strip mostly hoping to break end up with 300 ish hp and slightly better fuel mileage. would I be smarter to run 11.5:1, stock, or the 12.1 I had planned. the car will probably be out of boost most of the time and didn't want to give up the low end.
Linearburn and what fuel are you expecting to use?
@@mareksumguy1887 prob e85 altho if i can I would be nice to be able to switch to regular pump gas with just a change in ecu pramiters
Linearburn these Honda engines are highly strung from factory. I wouldn’t dream of increasing comp ratio when adding boost to a already high comp engine. I doubt you’ll get to 14 psi on a 11:1 K20 with E85. You’ll probably reach MBT at like 11 psi.
i think you need to understand about level of combustion accure in different level of compression. i know when we increase compression ratio, it will degrease swept volume like you what you say. but its just make tiny different than increase compression. if compression increase, level of heat combustion will do.
i am study in mechanical engineering. so i know about this.
It's about cylinder pressure not compression ratio. The bigger the cam in duration the more compression ratio your need to maintain a given cylinder pressure.
Acuérdense que hay comprensión estática y dinámica
@@jorgesalcedo5614 Duh
Nice guys!
Before I view your video; I must emphasize an evident need of a multiple fuel types injecting systems of tweakings on an automatics management programing capabilities. And also; why isn't there a weighted type of piston or a ram system that cranks cocked a load that keeps a force or anything that makes more sense than top dead center being the combustion instead of the chamber being on a up down cycle as an also application where one's combustion is diverted as channeled within the last one before's chamber that it also had done the same(a need for 16 for 2 cycle and 32 pistons for a four cycle would be needed for this) ........... It takes such shallow concentrations in order to advance logistics of combustions engines; that I realised another while writing this. It's the chamber that needs to drive a crank driver; of or and an engine should be a drive motor.Cheers
Did you use a Chinese version of Google Translate for this text?
🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥great teacher!
I see not all heros wear capes
❤️it!🇺🇸
Is it true that higher compression ratio only helps more or less below 5k rpm?
Not really but it's where the help is usually most needed.
How much compression ratio is the best
is that like a actual university?
Beware of the Crickets😳 if the guy in the other lane has crickets coming out the pipes at idle be very aware
I can't see shit with the fish in the way
This is why we turbo Méxican nissans engines with mexican stock ratio of around 12@1's like is nothing...
😂😂😂😂
Qué motores tienen una compresión tan alta? Hablas de las np? 👀
@@isabellab617 Nissan México mini trucks late 90's
@@djohnnineonesix820 yeah, those came with a KA24 or something similar, those are the NP300, or Hardbody D21
@@isabellab617 I don't know if we are talking about the same truck/engine.
Hardbobys were different trucks imported to Mexico from the USA.
And it was a totally different trim than the panel mexican truck.
Mexican Nissan panel trucks were made for heavy duty.
Higher compression for fuel economy and short gear ratio specially 1st and 2nd for heavy loads.
Engine were totally different than the one on the USA market Hardbobys.
I owned both.
And the brochure of the Mexican panel truck said near 11+ to 1 comp ratio.
I just square it to 12.
It doesn't said what engine series was but is all I remember.
Plus I'm not going to argue about it.
We use to load these trucks with 2+ tons.
And not problem moving that weight on my town hills... Or around los Altos de Jalisco...
Hardbobys where faster but not stronger with heavy loads.
And also my street truck was a 76 gmc high Sierra 4x4 that I swapped in a 700r4 MD8 and a rare 327 4 main bolts engine.
Now tell me " these 327 with 4 main bolts on the crankshaft doesn't exist"..
Yes they do exist. I owned one..
It was a from a late 60's corvette.
But that's Arina de different costal.
I was racing 1/4 of mile on 4x4 in 1996. Now is the trend in the USA 😂😂😂😂😂
Fantastic thank you
Our pleasure!
I want square pistons , square valves. Why wouldn’t this work and why hasn’t it been attempted?
why diesel engine run on lean mixture?
"Quench Pads"
What a bunch of disrespectful people in the class....
Yes untill detonation or preignition comes knocking on your door
This people don’t have no respect in that room
Would have been better if you went threw the maths how you found the loss in power on high boost etc
You could be chatting crap lol but good content thanks again