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Old 02-17-2014, 06:05 PM   #1
TheJackDaniels
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What makes your exhaust so special?

Reading through posts on here I couldn't find much info on what actually shapes an engine's exhaust note...For example the glorious benchmark that is the Subaru STI exhaust tone. What factors create its iconic tone? Obviously engine size yes but even the 2.0l motors sounded great. I can't imagine the fact that the cylinder arrangement is what creates the monstrous tone...


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Old 02-17-2014, 06:25 PM   #2
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I do believe it's the size, arrangement and firing order. Same with the old vw motors. Just have a different sound
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Old 02-17-2014, 06:28 PM   #3
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Combustion chamber shape, Combustion pressure, Ignition offset, Exhaust pulse path.

In a I4, traditionally at some point all the pulses merge together. If that point it located in such a way that and in such a point that pulses match (either aligned peak to peak or peak to valley), nothing done from that point back will change the sound much. Intensity of the sound will be the only change.

In a H4, the manifolds are designed in such a way that the exhaust pulses are offset slightly. One bank meets the other between a peak/valley and does not cancel.



This is a good video example of the difference:

YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.
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Old 02-17-2014, 06:34 PM   #4
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So essentially the unequal length headers is what causes the sound?
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Old 02-17-2014, 06:40 PM   #5
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For the most part.

http://www.indiana.edu/~emusic/etext...r1_waves.shtml

There's some decent information in there that can explain much better than I can.


The basics are,
Bore determines tone. Large bore, deep tone/pitch. Small bore, jar of bee's.
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Old 02-17-2014, 09:17 PM   #6
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Quote:
Originally Posted by iminhell View Post
For the most part.

The basics are,
Bore determines tone. Large bore, deep tone/pitch. Small bore, jar of bee's.
Think big block V8 and weed eater.
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Old 02-18-2014, 12:08 AM   #7
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Harley, BMW flat twin, inline 4 "crotch rocket". Harley tried to patent it's sound.

Honda's old CX500 twin, and all it's versions, sounded like a V8 at the local racetrack when it revved up due to the V angle & crank setup. The high RPM it ran at gave sound pulsations like an engine with more cylinders turning slower.
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Old 02-18-2014, 12:16 AM   #8
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That was a whole jar of knowledge just opened up there. I believe i have learned more just now than 4 years of automechanics in high school
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Old 02-18-2014, 12:22 AM   #9
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Seriously. I paid for college classes and still had to ask this simple question. Thank you for the schooling gentlemen. (Or women)

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Old 02-18-2014, 12:27 AM   #10
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Yea thanks everyone!
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