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Exhaust sound manipulation

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FlightBikes

FlightBikes

Mechanical
Joined
Feb 13, 2016
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Im working on tuning sound of an exhaust system. If you've ever heard the phrase "music to my ears" well thats what im aiming for. Hope you guys can provide some feedback.
So most exhaust systems from 99% of mfgs, simple just make the tubing bigger and use different "packing" for mufflers. Sounds like crap to me.
My challenge is to make an Inline 4 cylinder, sound good. Its easy to make a v8/10/12 sound good, but the 4 is a little tougher. so Im trying to think this out methodically and experiment with outside the box techniques.

So for example I have a 750cc i4 motorcycle, which has a pretty short stroke (compared to most other 600/750 bikes) and it sounds pretty darn good, almost F1 like But the engine im working on is a 2L, with a fairly square bore/stroke. and it sounds quite tractor like. I realize there are factors that I can't change, such as the bike reving at 3X the rpm, and the smaller pistons etc. SO im looking for other ways that I can manipulate the sound. So I am thinking of it as a musical instrument.

Unfortunately I can't experiment with every idea, so Hopefully you all can help lead me down the path to ideas that have a better chance of working.

my first thought is related to tubing size. for example I have heard the sound of a 3" single tube. But what if I was to use 3, 1.5" tubes?

 
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Yer hurtin' fer about four cylinders.


Mike Halloran
Pembroke Pines, FL, USA
 
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"my first thought is related to tubing size. for example I have heard the sound of a 3" single tube. But what if I was to use 3, 1.5" tubes?"
I don't see how you can attempt this project without understanding acoustics, and that statement reveals that you don't! Do you have any instruments (sound meter, recorder, analyzer)? Have you recorded and analyzed over motorcycle sounds like the Harleys and BMW? If you are restricted to a specific engine, then why not measure and analyze that engine with stock exhaust system to understand your baseline, both sounds like and measure characteristics?

Walt
 
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Do bear in mind that Harley Davidson sued for trademark infringement against Japanese motorcycle manufacturers for synthetically generating the "Harley" sound. They didn't succeed, as far as I know.

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529
 
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A lot of factors can be manipulated to make the engine sound differently. Cam profile matters. Header pipe length and merge points matter a great deal in phasing the pressure waves and sound waves.

Have you ever heard of 180 degree headers? They make crossplane crank V8s sound a lot like flat plane crank V8s (hence the 180 degree name). Id imagine the sound of a crossplane V8 could be strikingly similar to a flat plane V8 if a 180 degree intake manifold were used in conjunction to the 180 degree headers, among other tools.


"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
 
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I was following a MX5/Miata on my way home last night. The owner had gone to town with the exhaust system and it still sounded like an I4 trying to play with the big boys. Not enough revs available to make it sound good.

Steve
 
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Have you ever heard a flat 4 Subaru engine with a good exhaust?

Its definitely not a V8 sound, but it is as good as a 4 cylinder can get

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
 
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Please specify where you want to hear the sound from? Is it from the driver's seat while driving or out side passby noise?
Is the vehicle manual or auto, sedan, pickup or hatch back, 4x4,2x2 or low rider?
 
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I agree, most 4 cyl (car) engines sound crummy and cheap.

Maybe headers that pair cylinders with uneven firing orders to give that V-engine rumble.

There may be a penalty in power and/or uneven combustion because of uneven cylinder scavenging, though millions of V8's seem to have gotten along fine.
 
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