exhaust sound

[joshf2]

what characterises the way the exhaust sounds in a motor?

when i say this, there are different tones when the engine is under load, when its not under load, and when its under compression braking etc.

understandably, its "loud" when under load, ie WOT, but what about when its nearly silent in a small half-throttle range. im really hoping this makes sense.

and then theres a different tone when engine braking. and what causes the burble and pop on over-run...?

just curious

[Mechan1k]

Exhaust pulses change in frequency ... sound changes with this frequency as well.
Maybe with backing off you get there can be a fraction of a second that unburnt fuel escapes through the exhaust valves and ignites in the headers/extractors (then echoing out the reminder of the exhaust during the explosion.

Comes down to cam and valve timing and firing order too ... lumpier cams give off a different exhaust sound at idle ... and through out the rev range as well compared to standard.

There are many factors that can make the changes to the sound of the exhaust (and to the engine too).

I have only mentioned just a couple really.