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johnc

More Cylinders, More Power?

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Given the same levels of technology:

 

The V12 will have more bearing surface area than a V8 or V10 (longer crank, more connecting rods) meaning more friction.

 

There's also an increased amount of friction from the cylinder heads (longer cams, more lifters,valves, etc.

 

Clearly, we can't assume friction levels are equal even with the same ring/cylinder circumference.

 

I, as well as many others also agree 100%. The 12 cylinder would most likely bring more friction to the table which would absorb more energy from the combustion events, therefore less of that overall BMEP at the flywheel to accelerate the vehicle. (How much more depends on bore to stroke ratio, bearing diameter and widths, bearing speeds, etc. So many variables that will influence that, I think we should just leave that portion out for now.)

 

In narrowing down the power difference between the 12 cyl vs 10 cylinder, if we left the friction aspect out of the equation, (which is how I interpret the original intent of this thread), the argument is; "A V-12 makes more power than a V-10 because it has more power pulses per complete otto cycle, (720 degrees of crankshaft rotation)."

 

Personally I am not seeing that. And then throw in the frictional aspect and dynamic mass as well, (accelerating more valves, compressing more valve springs, etc), just another nail in the 12 cylinder coffin. So regardless of friction, the arguement was a V-12 makes more power than a comparable displacement V-10.

Edited by BRAAP

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In the context of Formula 1, its true. I just checked another related article in Race Tech and it comes to some similar conclusions. There are negatives associated with a V12 layout (length of the engine, additional weight) that sometimes offset the additional power provided.

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John, does either of the articles explain why the greater number of smaller pulses produces more power?

 

I'm not trying to be argumentative, I just can't get a handle on how that works. It's kind of like the 4-7 firing order swap currently fashionable among the chevy crowd.

 

John

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I kinda covered it above. In the Formula 1 world everything in the combustion process is optimized to the point that any bore size over 98mm doesn't produce any more power (IMP) and reduces thermal efficiency (more fuel, not more power). The reason is that there isn't enough time (10,000 to 18,000 rpm) for the flame front to complete its job if it has to travel through a larger combustion chamber. NASCAR ran into similar issues with their 10,000+ rpm engines. More fuel but not much (if any) more power.

 

This also translates into lower rpms if the combustion process is highly optimized and is true for very large diesel engines (MTU and MAN).

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Thanks for the further explanation. After reading post 13 & 24 a few times and a good nights sleep, the lightbulb is beginning to flicker on for thickhead here.

 

There has been some discussion of the same problems with the speed of the combustion events among large bore V8 engines, like the mopars and pontiacs. With 4.5 and 4.6 bores, the same thing is showing up at roughly half the F1 rpm levels. It seems shorter rods with less piston dwell time bandaids the problem in the stockers.

 

Thanks,

 

John

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If the volumetric efficacy is the same on any given engine and you are producing 80hp per cylinder, then it makes sense that:

1= 80hp

2=160hp

3=240hp

and so on.

 

The differences are of course are rotating mass and friction from more surfaces.

This dose not change the potential from any given amount of cyls., and the losses will not equal or out perform the gains from more clys.

 

If I'm off base, I know I will hear about it;)

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I kinda covered it above. In the Formula 1 world everything in the combustion process is optimized to the point that any bore size over 98mm doesn't produce any more power (IMP) and reduces thermal efficiency (more fuel, not more power). The reason is that there isn't enough time (10,000 to 18,000 rpm) for the flame front to complete its job if it has to travel through a larger combustion chamber. NASCAR ran into similar issues with their 10,000+ rpm engines. More fuel but not much (if any) more power.

 

This also translates into lower rpms if the combustion process is highly optimized and is true for very large diesel engines (MTU and MAN).

 

 

 

That makes sense, John. But the advantage is because the 12 makes more efficient use of the bore/stroke combination, not because there are more frequent firing pulses. That's my take, anyhow.

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3) Induction and/or exhaust pulse tuning/scavenging attributes of the V-12 allowing more "natural supercharging" effect, =more power

 

I assume by "natural supercharging" you mean achieving volumetric efficiency above 100% at a certain point(s) in the rev band. I would think that this phenomenon is a much stronger function of runner geometry than amount of cylinders, since this effect comes from pressure pulses caused by the resonance of the runners.

 

As for the main topic, I would think that the V12 would be at a disadvantage in terms of the frictional losses already mentioned. At some point, having more cylinders will give diminishing returns.

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John. But the advantage is because the 12 makes more efficient use of the bore/stroke combination, not because there are more frequent firing pulses.

 

I would depend on the displacement/stroke limitations imposed by the rules.

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There has been some discussion of the same problems with the speed of the combustion events among large bore V8 engines, like the mopars and pontiacs. With 4.5 and 4.6 bores, the same thing is showing up at roughly half the F1 rpm levels. It seems shorter rods with less piston dwell time bandaids the problem in the stockers.

Not sure about the F1 engines, but I do recall finding a long list of NASCAR engines and their rod ratios, and they were all 2:1 or above. I think it is safe to say that the higher the rpm limit the longer the rod and the higher ratio you want. Not sure if/how bore size factors into that equation.

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You're right about the nascar engines, I was referring to big blocks. Somewhere, maybe Popular Hot Rodding, there was a long discussion about Jon Kasse's engine that won the enginemasters competition. It was a large bore/short rod combo that was chosen to minimize detonation, since they had to run pump gas. There was a good discussion of chamber design, flame propagation, piston dwell and the effects on power and detonation. These were big cubic inch low rpm engines, especially compared to F1 engines.

 

I'm pretty sure nascar limits bore size to 4.185" max.

 

jt

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I used to believe in all of the above theories and set forth to assemble such a V12. Some of you may have seen it. In all truth and a life time of hot rod learnin … the SB mopar V8 was just plain faster. I think if I were to start all over again, the small block LT1 (or variant) would be the way to go.

I would have to say for the record as one who’s been there, the V12 will not produce more power. But open the hood on a V12 and everyone says holy crap!

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I used to believe in all of the above theories and set forth to assemble such a V12. Some of you may have seen it. In all truth and a life time of hot rod learnin … the SB mopar V8 was just plain faster. I think if I were to start all over again, the small block LT1 (or variant) would be the way to go.

I would have to say for the record as one who’s been there, the V12 will not produce more power. But open the hood on a V12 and everyone says holy crap!

 

What was your buget?...cause that plays a big role..plus the fact that v12 is pretty much uncharted waters...I remember years ago the 4cylinders were frown upon when it comes to racing....in the 80's know one would take a 4 over a 8...now that people are putting fort an effort into these engines, it's amazing what a 1.8-2.0 can do..im talking 1000+hp..do you think anyone in the 80's thought this was possible?? 4's are affordable now so that spurs growth..Back then it was just easier, cheaper and smarter to get your garden v8 and mod that

 

The v12 biggest enemy is cost..it's not really worth it to even try to make a v12 powerful cause a 8 can do it cheaper...But i do think a v12 would be more powerful given the same cost, knowledge and avlibility..plus the fact that all the v12's you can get fairy cheap are crap engines...that doesn't help....

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What was your buget?...cause that plays a big role..plus the fact that v12 is pretty much uncharted waters...I remember years ago the 4cylinders were frown upon when it comes to racing....in the 80's know one would take a 4 over a 8...now that people are putting fort an effort into these engines, it's amazing what a 1.8-2.0 can do..im talking 1000+hp..do you think anyone in the 80's thought this was possible?? 4's are affordable now so that spurs growth..Back then it was just easier, cheaper and smarter to get your garden v8 and mod that

 

The v12 biggest enemy is cost..it's not really worth it to even try to make a v12 powerful cause a 8 can do it cheaper...But i do think a v12 would be more powerful given the same cost, knowledge and avlibility..plus the fact that all the v12's you can get fairy cheap are crap engines...that doesn't help....

 

Dot's car is kind of legendary, I believe it was a Jag V12. Truly an awe inspiring build, I wonder if the new owner knows about HybridZ...

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the greater the number of cylinders the greater the ability to aspirate the same displacement so a basic JZ engine (leaving out turbos) has 3 liters spread over six cylinders with four valves per cylinder (24 valves) and of course six spark plug and six injectors this yeilds aprox 200hp (not bad)

the 3 liter v12 in a 1958 Ferrari Testerosa has 4 valves per cylinder (48 valves) 12 spark plugs and 12 carb jets (which in that setup is aweful close to a injector) so the same size v12 has greater aspiration potential, has double the spark and better atomization of fuel and so despite it's greater bearing surface it makes more power 320 hp to be exact. obviously the two engines are not perfect comparisons but they do illustrate the point that it's easier to create a higher horsepower engine with more valves, spark plugs and injectors, than with fewer.

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Great analogy, thank you. That same concept “more aspiration potential” carries over the Datsun L-series. L20A 6 cylinder vs the L20B 4 cylinder. Very similar engines in design and architecture, both are 2.0L displacement, but the L20A brings to the table 2 more intake ports and valves and 2 more exhaust ports and valves to breathe through, (the ports and valves are smaller for the 6 cyl but the overall port area and open valve curtain area for the 6 cyl is still greater than the sum of the 4 cylinders ports/valve curtain area), which does seem to offset the additional friction of 4 more valves and corresponding components, 2 more pistons with rings, bearings, etc. In those examples, the L20A’s greater aspiration is allowing for greater overall BMEP at the end of the complete 720 degree cycle vs the L20b. The L20b is short of breathe!

 

When comparing those two engine up to 3000 RPM, the advantage of the L20a is probably not as pronounced as it is say around 6000 RPM or 7000 RPM. Point being, usable rev range is contributing factor.

 

I can see how this principle applies to todays more modern multi valve, center spark bolt, more efficient burn chambers, etc, due to the even greater RPMs these modern engines spin. Regardless, elevated RPM’s for cylinders with larger displacement are going to require more time for efficient filling or they are going to suffer similar out of breathe “aspiration” issues as the L-20b suffers vs the L20a. So by adding a couple more cylinders that are smaller, now each can “aspirate” themselves more efficiently in the RPM range they running. :wink:

Edited by BRAAP

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Well this has been one of the most thought provoking threads that I have read!

 

On to my very uneducated opinon....... I would agree with the information given, that more cylinders = more power (keeping same displacement as stated) I would like to add that the frictional forces would become minimal due to the crank being up to speed making the end product "smoother". Adding more down force to the setup would increase the output in the end no matter what.

 

To resate it, I am pleased with the way this is going.

 

Hope my rambling makes sence to someone.

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More cilinders is a smoother running engine. Look for instance at BMW V12. But I guess it al depends on the purpose of the build. Like the V12 Merlin Airplane Engine ( Spitfire e.d ) is a rough running engine, but delivers massive torque.

 

I think the friction is irrelevant, maybe a loss of a few hp.

You can't say more cilinders is more power. Because the bore and stroke can variate.

You can have 4 liter V12 engines, and 11 liter V8 engines.

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There is one aspect I haven't seen in this discussion yet. Maybe it's here under another name that I'm just not noticing being the non-engineer type. Momentum. The distance between power pulses, 60* for a 12, 90* for an 8 for example. If friction and momentum is a linier function than it really dosen't matter. But if it's more of a hump shaped graph than you would want to catch it at some optimum slope on the curve. Since each subsequent power pulse would have to recoup the momentum lost from the previous pulse, a 12 cylinder engine would have less recouping to do than and 8, or 4 cylinder engine would. Thus more of each pulses' power would go to providing output than recoup. But again, this depends on what that graph looks like. If it's linier, the slope being constant, it really doesn't matter and I've just wasted everybody's time.

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