Engine Power Vs. Engine Displacement Vs. Engine Configuration

[Mr.Tiv]

Obviously displacement is one of those factors that make it so there is no simple answer. You need specific details and examples to be able to argue this intelegently.

[jediali]

In this situation you need to decide what your priority is? powerful engines tend to be easier to make because all you need is power and therefore fuel economy and cdonstruction costs are less important. I think the hardest engine design problems lie in the sports saloon and premium hothatch arena. Think about it, the new M3 and M5 sharing engine platforms, bmw 130i vs vw golf r32. There is a demand for technical sophistiaction as well as effectiveness.

Out of interest Porsche made a 2.5l inline 4 (with balancer shafts of course) and it was pretty good apparently. This engine redlined at 6200rpm i think. However manufacturers stick to about 0.5-0.6l per cylinder simlpy due to thier generic research in combustion. They simply impose similar stroke/bore ratios and combustion chambers on all their engines to allow mass compatibilty, eg see audi V8 and lambo V10. This of course applies to the big manufacturers like ford,vw,bmw, etc etc.

A more essay like, not technical contribution.

[henk4]

So your saying a 1.8 litre at 20lbs of boost will make more then a 6 Litre LS2 at 20lbs? A engine will still make more horsepower with more ci no matter if its n/a or FI.

no, if you want to increase the performance of a 2 litre engine you can go to a 3 litre engine or alternatively use a turbo, in which way you replace one additional litre displacement with a turbo....

[Slicks]

no, if you want to increase the performance of a 2 litre engine you can go to a 3 litre engine or alternatively use a turbo, in which way you replace one additional litre displacement with a turbo....

Right, forced indcution is only an alternative, not a replacement for [adding] displacement.

[henk4]

Right, forced indcution is only an alternative, not a replacement for [adding] displacement.

would you care to elaborate what in this case exactly the difference is between alternative and replacement? And it is far easier to add a turbo to an existing engine than to significantly increase displacement...

[group c n b man]

Where do I5 and V10 engines fit into this? All cars that are powered by V10s or I5s sound very smooth to me, or are they also inherently unbalanced.

[LeonOfTheDead]

Where do I5 and V10 engines fit into this? All cars that are powered by V10s or I5s sound very smooth to me, or are they also inherently unbalanced.

every engine can be "balanced", and theoretically perfectly too.
The balance could not imply a worst sound though.
Also...which V10 powered cars are we talking about?
I recall just the Viper basically, which doesn't have a very stressed engine therefore the unbalance could even be "hidden".

[hightower99]

every engine can be "balanced", and theoretically perfectly too.
The balance could not imply a worst sound though.
Also...which V10 powered cars are we talking about?
I recall just the Viper basically, which doesn't have a very stressed engine therefore the unbalance could even be "hidden".

I think he was talking about the engine configuration's inherent balance (i.e. without the use of balancing devices).

I guess it comes down to what you mean by "theoretically possible" but only a few engine configurations can be considered close to perfectly balanced with any realistically possible solution.

I agree that group c n b man is confusing sound with balance.

You can only think of a Viper?
What about BMW E6x M5? Lamborghini Gallardo? Porsche Carrera GT? Audi RS6? Audi S8? just to name a few...

Hmmm I would like to know why you think a Viper engine is not very stressed and how that could "hide" an inbalance?

[culver]

In case it hasn't been mentioned, balance is also not the only key to smoothness. With balance shafts an I4 can be balanced to the point where it's very smooth at idle. However, if you put a load on the motor at low RPM you can feel the power pulses. I believe the V8 is the first engine configuration where the pulses are close enough such that you never are taking power from the flywheel to keep the motor turning. The opposite extreme is the 1 cylinder motor where you are adding power only during the single stroke of the combustion process then using the inertia of the flywheel to move things along for the next 1 1/2 revolutions.

Things like engine mounting and all that also mater. A friend of mine has had a BMW 530 since new. It was glass smooth when new but over the years has grown rougher (not bad, just not as good as new). I suspect the engine mounts have become hard thus transmitting more vibration into the car. I don't think he lost a cylinder

[LeonOfTheDead]

I think he was talking about the engine configuration's inherent balance (i.e. without the use of balancing devices).

I guess it comes down to what you mean by "theoretically possible" but only a few engine configurations can be considered close to perfectly balanced with any realistically possible solution.

I agree that group c n b man is confusing sound with balance.

You can only think of a Viper?
What about BMW E6x M5? Lamborghini Gallardo? Porsche Carrera GT? Audi RS6? Audi S8? just to name a few...

Hmmm I would like to know why you think a Viper engine is not very stressed and how that could "hide" an inbalance?

Don't know why I didn't remember all of those engines, so silly.

I think the Viper doesn't have a stressed engine, or a high performance one if you prefer, not exactly because it has a huge displacement and less than 100 bhp/liter of displacement, but because the power and torque curve are very smooth and constant, basically.
In this way, as Culver pointed out somehow, the engine is working in a pretty constant situation, therefore the balance can be done more easily than on an engine revving from 1.000 at idle to 20.000 at it top rpm.

by "theoretically possible" I meant with proper balancing masses and balancing shafts, designed and mounted correctly.
With a good design, which is possible with every configuration, and a proper mounting, basically every motor can be artificially mounted.
The point is again trying to balance an engine which has to work in very different situation, which is basically impossible, and also, among many other reasons, why an F1 engine idles at 7.000 rpm.

In case it hasn't been mentioned, balance is also not the only key to smoothness. With balance shafts an I4 can be balanced to the point where it's very smooth at idle. However, if you put a load on the motor at low RPM you can feel the power pulses. I believe the V8 is the first engine configuration where the pulses are close enough such that you never are taking power from the flywheel to keep the motor turning. The opposite extreme is the 1 cylinder motor where you are adding power only during the single stroke of the combustion process then using the inertia of the flywheel to move things along for the next 1 1/2 revolutions.

Things like engine mounting and all that also mater. A friend of mine has had a BMW 530 since new. It was glass smooth when new but over the years has grown rougher (not bad, just not as good as new). I suspect the engine mounts have become hard thus transmitting more vibration into the car. I don't think he lost a cylinder

well said.

[hightower99]

With balance shafts an I4 can be balanced to the point where it's very smooth at idle. However, if you put a load on the motor at low RPM you can feel the power pulses. I believe the V8 is the first engine configuration where the pulses are close enough such that you never are taking power from the flywheel to keep the motor turning.

It is possible but most I4 engines in production don't really come close to truly balanced. Smooth? yes, truly balanced? no. besides it is not when the engine is sitting at idle that engine moves the most. Normally it is revving from idle that makes the most movement due to both inertial balance and torque reaction.

BTW: an engine is always using energy from the flywheel regardless of the number of cylinders. The main job of a flywheel is not to keep the engine spinning but to reduce the amplitude of combustion based vibrations. During a combustion cycle you have high pressure which decreases as the cylinder moves. You also have a lever arm that changes length during the stroke. This means that the force fluctuates. The flywheel's job is to even out these fluctuations.

So even V8s need a flywheel in exactly the same way as a 1cyl engine.

Technically an I4 has a combustion event every 180degrees of crankshaft rotation so you could make an I4 that always has one cylinder in the combustion phase. A V8 fires every 90degrees so it is possible to make one which always has two cylinders in combustion phase. Of course normally a combustion phase doesn't last a whole 180degrees (exhaust valves BBDC), so you really need 6 cylinders to keep one in combustion at all times and 12 to keep two in combustion at all times.

I think the Viper doesn't have a stressed engine, or a high performance one if you prefer, not exactly because it has a huge displacement and less than 100 bhp/liter of displacement, but because the power and torque curve are very smooth and constant, basically.
In this way, as Culver pointed out somehow, the engine is working in a pretty constant situation, therefore the balance can be done more easily than on an engine revving from 1.000 at idle to 20.000 at it top rpm.

Oh OK you meant High Performance... Stressed to me takes things like mass into account. I don't agree with the idea that if an engine has a relatively smooth torque curve that it is not a stressed engine.

What about the BMW N54? would you say it is an unstressed engine?

Not sure I agree that the viper has a particularly smooth output curves either. The balance thing about it being easier then if it revved up to 20K is to do with harmonic resonant frequencies.

[culver]

BTW: an engine is always using energy from the flywheel regardless of the number of cylinders. The main job of a flywheel is not to keep the engine spinning but to reduce the amplitude of combustion based vibrations. During a combustion cycle you have high pressure which decreases as the cylinder moves. You also have a lever arm that changes length during the stroke. This means that the force fluctuates. The flywheel's job is to even out these fluctuations.

So even V8s need a flywheel in exactly the same way as a 1cyl engine.

I'm aware of all that. The flywheel is always needed to dampen torsional vibrations however, in a V8 (assuming even firing) the combustion events are overlapped enough that their is always net energy coming from the pistons (assuming we are under some type of load) into the flywheel.
Torsional Characteristics of Piston Engine Output, by EPI Inc.

This is different than a 1 cylinder which needs the flywheel to carry the engine between combustion cycles. This also means the 1 cylinder flywheel must be comparatively heavier than that used in a similar power V8 (not that you normally compare V8s to single cylinder motors).

[LeonOfTheDead]

It is possible but most I4 engines in production don't really come close to truly balanced. Smooth? yes, truly balanced? no. besides it is not when the engine is sitting at idle that engine moves the most. Normally it is revving from idle that makes the most movement due to both inertial balance and torque reaction.

BTW: an engine is always using energy from the flywheel regardless of the number of cylinders. The main job of a flywheel is not to keep the engine spinning but to reduce the amplitude of combustion based vibrations. During a combustion cycle you have high pressure which decreases as the cylinder moves. You also have a lever arm that changes length during the stroke. This means that the force fluctuates. The flywheel's job is to even out these fluctuations.

So even V8s need a flywheel in exactly the same way as a 1cyl engine.

Technically an I4 has a combustion event every 180degrees of crankshaft rotation so you could make an I4 that always has one cylinder in the combustion phase. A V8 fires every 90degrees so it is possible to make one which always has two cylinders in combustion phase. Of course normally a combustion phase doesn't last a whole 180degrees (exhaust valves BBDC), so you really need 6 cylinders to keep one in combustion at all times and 12 to keep two in combustion at all times.

Oh OK you meant High Performance... Stressed to me takes things like mass into account. I don't agree with the idea that if an engine has a relatively smooth torque curve that it is not a stressed engine.

What about the BMW N54? would you say it is an unstressed engine?

Not sure I agree that the viper has a particularly smooth output curves either. The balance thing about it being easier then if it revved up to 20K is to do with harmonic resonant frequencies.

The N54 is turbocharged, twice, it's a whole different world there
And about the rest, I didn't say it wasn't so.
Also, while the flywheel is there to eliminate the torque's variations at the crank shaft, doing so, it must absorb and release energy, keeping the shaft spinning. Not its job, but surely an effect.

[hightower99]

I'm aware of all that. The flywheel is always needed to dampen torsional vibrations however, in a V8 (assuming even firing) the combustion events are overlapped enough that their is always net energy coming from the pistons (assuming we are under some type of load) into the flywheel.
This is different than a 1 cylinder which needs the flywheel to carry the engine between combustion cycles. This also means the 1 cylinder flywheel must be comparatively heavier than that used in a similar power V8 (not that you normally compare V8s to single cylinder motors).

I would like to point out that any 4 stroke engine with 6 cylinders has over lapping combustion events.

Also just because a V8 has overlapping combustion events does not mean that the flywheel is always getting a net increase in energy from the cylinders. A V8 has 6 or 7 cylinders that are absorbing energy from the flywheel at any one time. The later stages of a combustion cycle are not enough to produce a positive net influx to the flywheel.

Also I assure you that a 1 cylinder engine will run without a flywheel. It won't be smooth or stable but it will run. Ever seen the small engines used for RC vehicles? Alot of them are 1 cylinder engines and alot of them don't have flywheels.

[culver]

I would like to point out that any 4 stroke engine with 6 cylinders has over lapping combustion events.

Also just because a V8 has overlapping combustion events does not mean that the flywheel is always getting a net increase in energy from the cylinders. A V8 has 6 or 7 cylinders that are absorbing energy from the flywheel at any one time. The later stages of a combustion cycle are not enough to produce a positive net influx to the flywheel.

Also I assure you that a 1 cylinder engine will run without a flywheel. It won't be smooth or stable but it will run. Ever seen the small engines used for RC vehicles? Alot of them are 1 cylinder engines and alot of them don't have flywheels.

I think you need to review the links I include. Perhaps if the 6 pot motor has a significantly different power pulse shape it might always be net adding power to the crank. However, the illustration shown clearly shows periods where the net work of the pistons into the crank is negative. The V8 does not have those net negative periods of work.

You are bending the facts with the RC motors. First, most are 2 cycle thus don't have to go over 360 degrees before the next power pulse. Second, they do have parts that perform the job of a flywheel. ANY motor that can't continuously produce power needs to store energy during the power generation pulse in order to carry the motor through the rest of the cycle. An RC motor may not have a dedicated flywheel but the weight of the crank and other attached parts perform the same function.