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Discussion Starter #1
Hi all -

Just a question for those of you who know exhaust systems - how critical is pipe length to performance on a four-stroke?

On a two-stroke, the pipe length is very important, and you don't want to go around messing with it unless you know what you're doing. Is it the same for a 4-stroke?

I was looking at my new (old!) heap that I picked up (CB450), and was envisioning a two-into-one setup, but I don't know how that might affect things. What if I needed to make the pipes longer to route them correctly?

thanks!
 

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As far as length of the exhaust is concerned, I know of a couple Honda choppers running little more than the head pipes. Shorter/more open pipes may make the bike run a little lean, but its really kind of a get-it-running-and-tune-it-then type of deal. In other words, there's no way of knowing how it runs until you get it running...or something like that.

If I read you correctly, you are going to try to make your own pipes? Modify an existing set? Might be a tough job, especially 2-1. If you're just looking to ride it on the street and you've got a set, 2-1's are fine but I'd suggest getting it running with the stock headpipes and shorty mufflers. You got plenty of time for full custom pipes down the road.

Honda go sideways!

Edited by - krapfever on Dec 17 2006 8:43:23 PM
 

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About headers / exhaust pipes, a 4 into one is better than the stock configuration 4 into two because the colusion of pipes acts as vacumm helping in the riddance of gases more efficiently.Once a piston fires and exhaust stroke starts in one pipe , another cylinder already closed the exhaust valve and is heading into intake...just as it is closing its exhaust valve, the gases leaving the headers on that primary pipe go through the tail pipe and creat vacumm....aiding the next cylinder rid itself of gases as soon as the exhaust valve opens. It is a chain reaction.

Also, the lenght of primaries has effect on performance. ( primaries are the section of pipe that starts at the engine and ends at the junction, the tail pipe.)

Longer primaries are geared towards high RPM. Shorter primaries are geared for torque.

Cafe racer DOHC CB750F

http://cardomain.com/id/jaimesix
 

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Discussion Starter #6
Thanks, that's great info!


EDIT: and for the record, yeah, I gotta get it running first. Just pre-planning here, deciding how to spread out costs in a wife-pleasing fashion :)


Edited by - borzwazie on Dec 20 2006 12:07:20 PM
 

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4 into 1 doesn't work too well on a twin.<img src=icon_smile_wink.gif border=0 align=middle>
(ew, my first use of the little smiley things.... i feel ashamed)


2-1 should be no problem, lots of people run 'em on the honda twins. I'd post a pic of mine but it's already up here somewhere....






BORN TO LURK, FORCED TO WORK.
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Rosko,
You could run a 4-1 on 2 twins. Kinda like that Nazi plane they made by joining 2 fighters together at the wing tips to make a tow plane for big gliders. That way a gay couple could ride side by side. It might be cute.
Ken

AHRMA 412
Vintage racing - old guys on old bikes
 

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Another website with formulas, good stuff, mostly fiat based. They have some other good information too, but this most directly relates.
http://www.scuderiatopolino.com/Exhaust.htm

Length of primaries.

L=(1700)120/N N being desired RPM and L being length in inches...same as the other one I guess.

Diameter of primaries

V=(Piston Speed in feet per second)x(D2/d2)

V is velocity of gas, they say roughly 300fps is ideal.
D2 is the bore squared
d2 is the diameter of the primary squared.

Bring on the algebra!

I love the smell of 2-stroke exhaust in the morning...no seriously, I can't get enough of it.
 

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Another website with formulas, good stuff, mostly fiat based. They have some other good information too, but this most directly relates.
http://www.scuderiatopolino.com/Exhaust.htm

Length of primaries.

L=(1700)120/N N being desired RPM and L being length in inches...same as the other one I guess.

Diameter of primaries

V=(Piston Speed in feet per second)x(D2/d2)

V is velocity of gas, they say roughly 300fps is ideal.
D2 is the bore squared
d2 is the diameter of the primary squared.

Bring on the algebra!

I love the smell of 2-stroke exhaust in the morning...no seriously, I can't get enough of it.
 
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