Engine sounds

[Kris-with-a-k]

Hey guys, I have a genuine and frustrating problem I'm trying to figure out so I can start to model. ---How is just the exhaust sound from a car come from? (Yes, i know feom the individual explosions that are happening inside the combustion chamber, but its more complex). Also, why if your not in the right gear going up hill, and even tho your RPM hasn't changed, as you give it more gas, the engine note changes. ( besides the obvious answer because you're giving it more gas there's a more complex answer). And finally, what makes a Ferrari V8 sound SO different that a Chevy or Ford V8, excluding size and exhaust layout. I have an hypothesis. We will focus on one cylinder of an Engine of your choosing. Engine takes in air and fuel, its compressed to around 120psi, ignition, rise and heat are produced and the piston gets pushed down, ( (very simple introduction). However , as the piston is at bottom dead center and before the exhaust valve opens, there still remains a calculatable pressure that remains. Due to a volume of air now hotter than originally, there is still pressure inside the chamber. When the exhaust valve opens, rapidly even at idle and the piston is thruster upward, thoes hot exhaust gases, as hot as 50psi, are forced into the exhaust system and out the tailpipe. Now 50psi being forces out a narrow tube in ,even as low as .06 sec, is bound to "carry a tone" what do u think

[arc]

The Ferrari is capable of much higher RPM’s and for much more extended periods of time. This can only be done by very exacting design tolerances and assembling practices. They rather sound like what I would expect a very large high performance multi-cylinder motorcycle race engine would sound like if they had that much displacement.

[Scott of the Antares]

I think compression ratios within the engine will have an effect on the note as well as the exhaust.

[studiot]

The sound produced by an internal combustion engine is largely conditioned by the exhaust system.

The engine itself produces regular pressure pulses at a rate proprotional to the engine rpm, depending upon the number of cylinders or chambers (I once did some gas dynamics modelling on a rotary aero engine).

The pulses provide a forcing excitation of a (sometimes very) complex pipe and chamber system which has several functions, one of which is to maintain constant back pressure on the engine.

There are several proprietary programs dedicated to the analysis of the gas dynamics of exhaust systems.

The exhaust system usually has a helmholtz resonator to extract energy and reduce the noise of the machine (or enhance it in the case of motor sport / motor cycle machines)

Measurement of the noise accompanied by Fourier Analysis will result in a noise spectrum showing the engine input rpm and its harmonics, plus the effect of the resonators in the exhaust itself.

[Kris-with-a-k]

ok so. ive done some more reading based off what youve all suggested. What I am doing for right now is breaking the engine down to just ome piston.  I downloaded a program called  "engine analyser Pro". What it does is let you pick from a few engines or input the paramaters yourself. what is has told me about a single cylinder is that peak pressure inside the cha,ber during detemation is  1827psi @16.7* before TDC and the Cyl temp reaches 4502F.  The exhaust valve opens when the pressure is around 252psi and around BDC. That is where the Exhause Pulse is generated. hence, what we hear.   I want to build a single cylinder, with the paramaters of a chevy 350. So sat 4" bore and 3.48"stroke.  so each cylinder is 717 CC.

So lets say i made One cylinder 717CC. made it to match a chevcy 350. Filled it with 250psi and released an exhaust valve to evacuate all the pressure into an exhayse system that was the same as a camaro z28. I would then record that single pulse wave, and then add 7 more duplicates through an audio program.  Once i am able to at least simulate the 3rd stroke of the engine from one piston, i could be on my way to changing the pressure and release timing to simulate an inscrease in load.  I know there are alot of variables to overcome and math i must do. But technically it is possible to remake any engine that ever existed using one cylinder with the correct size {bore and stroke, valve timing, valve size, duration, and exhause shape. once i have a recording of ONE cylinder that works than skys the limit. Video games would sound so much better, movies would not have to buy a expensive mustang to do their shots, they coould use a v6 and my system woud make it sound like a v8. i wouold have full control of every cylinder, with ever p[ossible rpm and load. There is nothing that pisses me off more than seeing a video incar and the engine note is not even matched to the video...