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Discussion Starter · #1 ·
I was driving my gasser today and enjoying the exhaust drone on the freeway. Made me think about what exactly is it that causes noise out the exhaust anyway.
I know different exhaust systems and mufflers will sound different, as well as number of cylinders, engine size and gas vs diesel, but what is the root source of the noise?
From my understanding exhaust valves will typically open while the piston is still on the downstroke during the combustion stroke. Is combustion still occuring on as the valve opens and thats what you hear? or is it the physical sound of the exhaust gasses passing the valve? Why does a diesel sound different than gas? And why are rice burners so damned annoying -:t?
 

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There are actually pressure waves produced by each exhaust valve opening. The hot combustion gasses are still expanding when the valve "pops" and there's a pulse of expanding gas before the piston comes up on the exhaust stroke to shove the rest out of the cylinder. The sequence and timing of the multiple cylinders "firing" into the exhaust causes these pulses to compound, combine and reflect/nullify each other. The differences in temperature, pressure, timing and volume between a gasoline and diesel engine make the biggest difference. The turbo on the DMax also squashes and blends the exhaust resonance since it's a "choke point" in the whole system. Gasoline engines also have a lot of time and engineering put into exhaust scavenging design in the manifolds. Non-turbo diesels are a lot simpler, just "get it out." In addition to the scavenging design in the gassers, they actually "tune" the mufflers and resonators for sound. I can really notice the unique sound of a 5.0 Mustang vs. other gas engines.

As for the ricers - they just are. What do you expect when you run a 1-1/2" pipe off a lawnmower engine into a big chrome muffler with a 6" tip?
 
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