Not to sound dumb, but why do motors make noise. Is it the burning of the fuel.. or the air passing through the heads and motor... or the different parts moving around... or a combination of them all.

Why do engines sound different.. like the 4.6's or the V10 viper motor.. or our LS1?

Sorry again if this is stupid... just have always wondered that!

 

Not a stupid question at all, I've thought about this many times also. It's a combination of everything of course, with combustion being the major contributor. Any time you have the rapid expansion of gases as in an explosion of any kind, sound waves are generated if the explosion happens in an open area. An explosion is just very rapid burning. Since the valves open before this process is complete, you have plenty of sound output. The frequency or tone of the sound is based on the size of each explosion as well as how many of them occur per second. Cylinder size and charge density determine the size of the bang. The number of cylinders and rpm determine the frequency. In a V8, four cylinders fire for each revolution of the crank. In a 4 cylinder, only two cylinders fire. Camshaft design plays a big role because long duration cams dump the fuel into the exhaust while it's still burning. Even how the cylinders are aranged around the crank makes a difference; Harley's sound rough because they are a V-twin with much less than 90 degrees beteen the two cylinders, so the crank coasts then both fire in rapid sucession. Still another factor is the exhaust system dimensions; different length pipes have different resonant frequencies, just as in a pipe organ.

 

All moving parts create vibrations. Some of these vibrations enter into the audible range and can be heard as well as felt. Lifters, rockers, the friction of pistons, and the rushing of air create vibrations that one can feel, and hear. The most prominent of these is the combustion and expulsion of volatile gases through a exhaust system.
The combination of any set of vibrations might give one the sound/feel of a Camaro, or a Viper, etc. Because each vehicle has a set of parts different from any other vehicle, the composite vibration/sound will be different.

 

Yeah another thing too is with different car body designs the engine will sound different, because you have a different "interior resonance." If you have t-tops or a vert you can tell a real difference with the top out.

 

Thanks for the info.... i was not totally in the dark... but it is one of those things like... "How in the hell do this work"

 

As a side note, a couple of guys I know decided to save their Mom some money on installing a new exhaust sytem on a old car with a straight six. Just to yank her chain, right after they took the old system off, they told her it was fixed and called her over to listen. When they fired it up they thought it would blow her ears out, but it just quietly "gurgled" with it's worn, flat cam. The point is, cam design makes a huge difference. If you want to hear a good sounding engine, try a Ferrari V-12 dual-overhead cam at 7000 rpm!