Exhaust: Max.HP with Min.dB - how?

[Apolan]

thanx NoHachi, your knowlidge always appreciated

I just wonder how would such piping work with a stock header (for now)? Should i keep the oem middle section, to keep a 4-2-1 design, or should i have a 55mm pipe done from header on (with one straight throu muffler in the middle and a bafled one at the end) to make a 4-1 system? or make a new middle section wit 2-1 design? just draw something for me hehe

[NoHachi]

Its a 4-2-1 design, you can't just change the length/joins of the header pipes since those actually are calculated to give a nice spread trough the rpm range.

From there your plan seems sound. You can switch around between whatever muffler designs your shop has lying about to try and determine which sound appeals most to you. Having driven a car with a straight through exhaust for 2 years, never again will one find its way onto one of my cars. Noise should be produced by the intake, not exhaust. That way, the car is quiet during idle and cruise, but growls under full throttle.

[Apolan]

silly me, ofcorse.. so the diameter of the twin pipes in the middle part is fixed by the header. im guessing i should also keep the "oem" lenght of this "twin" section right? and when they join (as smoothly as possible) i should put cca 55mm pipe all the way to the back, using one straight through resonance muffler in the middle and a baffled type mufler in the rear. sounds good? sorry for overcomplicating things, but i need to determine every aspect of my build. knowlidge saves money.

[NoHachi]

That sounds ok. The diameter of the last section should be the same as the diameter of the collector at the flange, if that is 55mm then its fine. The length of the secondary tubes is also calculated (though less important then the primaries), so preferably leave those as they are.
Most difficult bit is finding mufflers that have the correct inner diameter and size.

[jamiemirror]

http://www.toda-racing.co.jp/jp/product/.../4ag-1.jpg
http://www.toda-racing.co.jp/jp/product/.../4ag-2.jpg

[Bean]

jamiemirror Wrote:http://www.toda-racing.co.jp/jp/product/.../4ag-1.jpg
http://www.toda-racing.co.jp/jp/product/.../4ag-2.jpg

I'd love one of those they're lovely but so expensive...
there's another system from toda whick uses the stock header and replaces the 2-1-1 bit of the stock item, very loud though as far as I've heard...

[jamiemirror]

Forget about expenses - look at tube sizing.

[NoHachi]

Its not just tubesizes Jamie, its tubesizes in combination with tube lengths. I believe you had acces to engine simulation software, try out several combinations and you'll find that these are interrelated.

What I do like about the Toda exhausts is the motorcycle style tube connections with springs. Best way of doing things.

[jamiemirror]

Agree NoHachi. But TODA were not so kind to publish all parameters of their headers, I found just these Better than nill.

[NoHachi]

Okidoki

Just found a nice illustration of why you want intake noise to dominate and an as quiet as possible exhaust. Check out these two video clips. Both of a miata (so 4 cyl), both made at the same location with the same camera and external microphone. Only diff is that one has the mic position right above the exhaust tip, while in the other clip the mic has been moved near to the intake.

Exhaust:
http://www.youtube.com/watch?v=ie1jyeUjwy0

Intake:
http://www.youtube.com/watch?v=em2Ri6bN2Xc