Same engine sound no matter the displacement

[Spitfire1]

I was wondering why is the same engine sound on 785cc and a 10.8 liter engine?

[Spitfire1]

With all else left unchanged and just changing displacement it always sounds like a 4 liter engine. I talk specifically about v8s. It to me sounds always like something like a 4.5 v8 no matter what you do with the bore and stroke.

[Killrob]

There is astonishingly little difference in engine sound as a function of displacement in real life too, so that's why it isn't modelled as a dependence in game.

[Spitfire1]

Originally posted by Killrob:

There is astonishingly little difference in engine sound as a function of displacement in real life too, so that's why it isn't modelled as a dependence in game.

So a 3.5 ferrari berlinetta from 1995 sounds different from a 7.0 LS7 c6 corvette because of the crank and also exhaust configuration and has nothing to do with size at all? I am just trying to learn here. There is a decibel difference and bass increase with more size surely.

It is somehow hard to believe that. A 785cc tiniest v8 has same sounds as a full fat ls7 or a 10.8 liter V8 all else being equal. I just don't see it.

[Scraig]

Originally posted by Spitfire1:

Originally posted by Killrob:

There is astonishingly little difference in engine sound as a function of displacement in real life too, so that's why it isn't modelled as a dependence in game.

So a 3.5 ferrari berlinetta from 1995 sounds different from a 7.0 LS7 c6 corvette because of the crank and also exhaust configuration and has nothing to do with size at all? I am just trying to learn here. There is a decibel difference and bass increase with more size surely.

It is somehow hard to believe that. A 785cc tiniest v8 has same sounds as a full fat ls7 or a 10.8 liter V8 all else being equal. I just don't see it.

Considering that like 95% of engine sound is exhaust, I don't see why it's that hard to believe.

[Remmelnator]

Originally posted by Scraig:

Originally posted by Spitfire1:

So a 3.5 ferrari berlinetta from 1995 sounds different from a 7.0 LS7 c6 corvette because of the crank and also exhaust configuration and has nothing to do with size at all? I am just trying to learn here. There is a decibel difference and bass increase with more size surely.

It is somehow hard to believe that. A 785cc tiniest v8 has same sounds as a full fat ls7 or a 10.8 liter V8 all else being equal. I just don't see it.

Considering that like 95% of engine sound is exhaust, I don't see why it's that hard to believe.

Right, and the fact that bigger engines sounds different is also because they have bigger exhaust. The intake can also change the sound quite a bit but engine size hardly does.

[InitialYeet]

Yeah, its because of crank and exhaust.

[Dr. Dingo]

Watch some videos of model engines, they sound just like tiny little versions of the real things.

Engine sounds are mostly dictated by complex exhaust and intake design, but things such as crank offset and firing order (ie. "Big Bang" conversions) have the most direct effect on noise.

[Swartkin]

i think we should have different exhaust note depending on the exhaust size, having a 3.0L v8 sounding like a big 6.2L V8 is quite weird, if we already have that, it's not very noticeable

[Spitfire1]

Originally posted by Swartkin:

i think we should have different exhaust note depending on the exhaust size, having a 3.0L v8 sounding like a big 6.2L V8 is quite weird, if we already have that, it's not very noticeable

Also that. Changing exhaust diameter seems to have no effect on sound.

[T_Eighteen]

Originally posted by Spitfire1:

Originally posted by Swartkin:

i think we should have different exhaust note depending on the exhaust size, having a 3.0L v8 sounding like a big 6.2L V8 is quite weird, if we already have that, it's not very noticeable

Also that. Changing exhaust diameter seems to have no effect on sound.

Thats because majority of the exhaust notes come from the exhausts exiting the combustion chamber and into the headers/downpipes. Changing the diameter doesn't really have a drastic effect. The diameter mostly changes the back pressure, hence why you see an increase or decrease in power depending on the adjustments you make to the diameter. The change in tone isn't effected at all, or if very little.

[Spitfire1]

https://www.youtube.com/watch?v=qAu4iPV804w

[Killrob]

Thanks for the perfect example proving my point :) If that engine is 1/5 th scale, that means it is 1/5^3 the capacity, i.e. 1/125th the capacity! That little engine will have a much higher idle, as you do hear in the video, but other than that and a tendency to accentuate some higher frequencies due to the much smaller components involved, it does sound very similar to the 125x larger (capacity) original if it ran at the same RPM.

[Swartkin]

Originally posted by Killrob:

Thanks for the perfect example proving my point :) If that engine is 1/5 th scale, that means it is 1/5^3 the capacity, i.e. 1/125th the capacity! That little engine will have a much higher idle, as you do hear in the video, but other than that and a tendency to accentuate some higher frequencies due to the much smaller components involved, it does sound very similar to the 125x larger (capacity) original if it ran at the same RPM.

I don't think the sound of the car in the video was caused by RPM, atleast not much, it has to be at 4500Rpm or so in idle, and the car still sounds way less agressive than a full size v8, i think it has more to do with the exhaust

[Spitfire1]

Originally posted by Killrob:

Thanks for the perfect example proving my point :) If that engine is 1/5 th scale, that means it is 1/5^3 the capacity, i.e. 1/125th the capacity! That little engine will have a much higher idle, as you do hear in the video, but other than that and a tendency to accentuate some higher frequencies due to the much smaller components involved, it does sound very similar to the 125x larger (capacity) original if it ran at the same RPM.

Bigger displacement has a lower pitch as well as higher volume.

[Killrob]

Originally posted by Spitfire1:

Originally posted by Killrob:

Thanks for the perfect example proving my point :) If that engine is 1/5 th scale, that means it is 1/5^3 the capacity, i.e. 1/125th the capacity! That little engine will have a much higher idle, as you do hear in the video, but other than that and a tendency to accentuate some higher frequencies due to the much smaller components involved, it does sound very similar to the 125x larger (capacity) original if it ran at the same RPM.

Bigger displacement has a lower pitch as well as higher volume.

Not to first order, no. Higher volume yes, because there is more airflow in total. The pitch is primarily a function of the RPM and firing order, not the size. The Helmholtz resonance frequency certainly is a lot lower on larger engines (so high its not audible on the RC engine you linked), but that is on the intake side only for the sound and a secondary effect.