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Discussion Starter #1
The id measurement of the head pipes on my cb/cl350 is 1 1/4". If I were to run these into mufflers id measurement of 1", what kind of issues would I run into? Several mentions have been made here as to the lack of benefits running less restrictive exhaust systems on 350s, since they require some back pressure. My motor is stock with velocity stacks & no filters (a no-no I'm aware of). The mufflers are from a Kawasaki ex250, and I have no idea how restrictive they are.
 

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How do you physically intend to manage that? If they're megs are your plan is to cut them up to a point where the ID exceeds the OD of your header, no problem (though there's no guarantee that your performance isn't adversely affected). If on the other hand the plan was to run the muffler mount inside the header (as opposed to the other way around), I'd advise against it. Muffler restrictions are designed to slow air down in an orderly fashion... nothing orderly will happen if you force the air into a narrower tube than it was previously traveling down. Furthermore, the narrower the exhaust path, the faster air travels and the louder it is (which is why mufflers expand). You won't be doing yourself any favors in terms of noise.

...but of course I'm making some assumptions here. What's your joint scheme?

A
 

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Discussion Starter #3
The inlet on the mufflers nearly matches the exhaust header, then narrows just past the joint. My initial thought was that the decrease in pipe diameter would speed up the exhaust gases - much like a venturi in a carburetor. If that's the case, and the only drawback is louder exhaust, I'm tempted to give it a try. On the other hand, if the smaller pipe diameter is going to create so much back pressure that my engine performance suffers, I might think about cutting into the mufflers to the point where I could replace the inlet pipe with something a little bigger.
 

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Discussion Starter #4
Nobody else has any input here? No one even, who designs & fabricates custom race exhaust systems?
 

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OK, I'll throw in my 2 cents worth here. On my racebike, the 2-1 system I cobbled together works much better than the stock headpipes with crappy megaphones did. That being said, I don't like my current system much. It is routed poorly so I can't get a good belly pan fit and it is UGLY. So based on what JohnnyB said about stock headpipes being big enough to handle the flow, I want to put a set of stock CL header pipes on it with some Supertrapp megas and see how it does.

Ken

AHRMA 412
Vintage racing - old guys on old bikes
 

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I'll try to help. Even though I don't build exhaust or know anything about CB 350s.

If you're talking stock 250 mufflers I don't think anything you do to them short of gutting will make them loud.

I'd figure theoretical CFM for both applications. The 250s smaller but turns much more rpm. CFM= rpm x displacement/3456 Displacement is in cu in. in my formula, you'll have to convert it to cc. That's also figuring 100% VE, but I don't have any idea of a realistic VE # so lets pretend they're both 100% efficient @redline. The 250 is surely the more efficient motor anyhow.

But aren't the 250 mufflers huge and heavy?

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