I was looking through the different N/A engine rebuild threads here, and in my350z, and I started wondering: what would these engines sound like? With luck, someone has some experience and can shed light on the pitch differences. (Numbered to separate my thoughts ) Please let me know where I am wrong.

1- Less restrictive intake and exhaust seem to take the engine closer towards what the engine would sound like if no intake or exhaust were attached. This coupled with temporary pitch changes from reinforcement and resonance due to overlapping of reflected sound waves.

2- The number of cylinders is not related to the tone, just the sound consistency. When a harley is stopped at a light, it sounds very similar to an old muscle car, except that it appears to be stuttering. My assumption is that this is because the cylinder size is the same, but the number of pulses is four times less than it would be on an old v8.

Here is where I start to have trouble forming concepts

3- Bore and stroke are interchangeable when comparing sound because the volume of a single pulse will be the same. Here is a drastic example for contrast (I realize these numbers are not possible):
1" bore, 8" stroke, 8 cylinders = ~200ci
2" bore, 2" stroke, 8 cylinders = ~200ci

4- While it has the same "note" the larger bore will have a sharper tone than the longer stroke, because it will take less time for the air to evacuate the cylinder (more shallow) than it would if the stroke is longer.


I realize I am making quite a few unfounded leaps here, and expect be wrong on several of them (if not most or all.) Many thanks to anyone with the experience, knowledge and time to correct this.
-Boog

 

"The number of cylinders is not related to the tone, just the sound consistency." ???????

The frequency depends on the rpm since a V6 has 3 events [intake and exhaust] per rpm and frequency of noise is speced as so many events per second. Obviously a V6 generating 30 HZ is lower than a V8 generating 40 HZ at 600 rpm [10 RPS].

Remember the exhaust is forced out by heat expansion when exhaust valve opens not the piston, same with intake the earth's atmosphere rushes in with a 9-14.7 psi pressure to fill the empty space in cylinder.

Bore and stroke just define the space.

 

Thanks for your input.

This would mean that a 1.5L, 4 cylinder engine at 6k RPM would sound the same as a 5L, 8 cylinder engine at 3k RPM. So, displacement must have an impact.
I guess I was looking for how it changes the sound, rather than just "the larger the displacement, the deeper the sound."

Lets say we have two V6 engines, one with a larger bore, but less stroke, and one with a smaller bore, but more stroke. If they have the same displacement, will they sound the same at the same RPM?

Any more details you can point out, or suggested reading would be appreciated.
-Boog