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Wow...no matter what I entered in there... CC's, CID, etc it gave me some whacky ass numbers. Like an exhaust pipe 2.5" long and .15" in diameter.

Entered the numbers for a 400 CID V8...it gave me 8" primaries a little more than 1/2" in diameter.

JohnnyB
 

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By the way.... for the typical Honda twin, primaries about 22-26" long seem to work good. Shorter to enhance high rpm power....longer to enhance lower end power.
JohnnyB
 

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Discussion Starter #6
I ask because I know what the standard pipes available are, and there are a few formulas out there. For my project the numbers come up shorter than what is available over the counter. Even with the mid-range enhancing length. Just wanted to check the numbers. For what it is worth I like this calculator:
http://www.mez.co.uk/mezporting/exhaust_length.html

BORN TO LURK, FORCED TO WORK.
www.NYCvinMoto.com
www.VinMoto.org
 

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just to throw this out at you; got these when i was at MMI many moons ago.

primary pipe length=P

P= [850x(exhaust opening angle+180deg)]/rpm; or:
P=850 x the total of exhaust opening angle plus 180 degrees, all divided by desired rpm of operation.

pipe id={sq rt of[cc's/(Px25)]}x2.1; or:
pipe id equals the product of the root of cc's divided by Px25, all multiplied by 2.1.

is that clear?

if at first you don't succeed, use a bigger hammer
 

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fr, maybe if both of us get together, we can find someone who can do this for us.

jc

i dont know shit
 

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Pete...I'm gonna save that post. I've been wanting to write a piece of exhaust software to go along with my Helmholtz resonance software for calculating intake track length.
Tuning for Speed has some similar info.

You know what I've done in the past. Find a good picture of a factory race bike of similar displacement and cylinders to yours....import it into a CAD program....scale it using the rim size....measure the primary pipe length, megaphone length and taper.

I've even used calipers on the parts of high quality models of old Honda GP bikes....you'd be amazed how accurate they are.
JohnnyB
 
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