Modifying exhaust question | GTAMotorcycle.com

Modifying exhaust question

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PhyrexianMoto

New member
Hi all,
I have an honda cm250, 82 or 83, the one with the belt drive. It's been garage stored for many years, and during the holidays I've been tinkering with it, with the plan to get it up and running for spring. The exhaust pipes had welds were the pipes meet the muffler on both sides and these terrible welds were rusted and full of holes. Finding an exact replacement (i found one) is a little too expensive. I was hoping someone might know what the impact would be to replace the stock exhaust with 2 separate pipes that aren't joined together.
If you tell me I shouldn't do it, could you tell me if it could be cut, and new piece of pipe added at either of the 2 locations (yellow or red) indicated in the picture.
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Thanks
 
Iirc removing the cross tube will cost you some power. I'm not sure if it was tuned to a certain distance from the exhaust ports or just placed at a convenient location.
 
It might cost you a little performance, and you might not even notice. Is called the exhaust balancing pipe and what it does is increase the volume of your headers before reaching the muffler. How important that is? only Mr.Honda knows for sure, but it likely has something to do with how restrictive the Doh! the exhaust thingy is! <- stupid advertising virus won't let me type smuffler
 
The cross-over pipe, and its (relatively) exact location and size, are quite important for the way the pipe is tuned - and that's quite important for how well the bike runs. If you are going to the trouble of cutting out the rusty original and replacing it, put it in the same place as original and as close to the same diameter as possible.

Putting the cross-over pipe further downstream (longer header pipe) will theoretically make the exhaust pipe tune to a lower frequency (i.e. favour low end operation but cost top end power). Using two fully separate exhausts will make the exhaust tuning like that of a single ... hard to get right, and really favour low end over top end power. This is not simple. Don't try to re-engineer what Honda built.
 
I'll take everyone's advice and retain what I have.
Do you guys know if any old muffler shop will be able to make the kind of mods I have in mind? Specifically, cut from the red lines and remake everything that was cut away (mounting tabs, and the flared ends).
 
A normal run-of-the-mill automotive exhaust shop will have trouble with the small pipe diameter and the tapered shape. It's not something they normally deal with when putting an exhaust system on a car. The custom and hot-rod places (the ones that can do general custom fabrication) might be able to do it.
 
For a small motor I wouldn't goof too much with the exhaust, you will get yourself into tuning and maybe jetting issues that can be a lot of work to solve. Any muffler shop can do this, cut from the red lines on your pic and replace with a replacement swaged at both ends to the appropriate pipe sizes. I have had a few done at Global Muffler, Global Muffler Inc. -- it's not their main line of work but when I've walked in with cash, they have made me stainless adapter pipes for $20 each. No guarantee and I have no affiliation with them but it might be worth a try.

The toughest part is the mounting brackets -- Global does tube bending and swaging, I don't know whether they would cut and weld the brackets for you.
 
I can’t see the damage in your photos but I’d be tempted to JB Weld and/or exhaust tape over the holes and then cover with exhaust wrap.


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Patching up what you already have makes good sense imho.
I wondered if Woody might have a set but no way would they be in great shape anyway.
 
Can you post a real good pic and closeup of the damage ? Someone might be able to just weld in some patches ?

I expect anyone that does this for living is going to be 100 bucks an hour or more , and it looks like more than an hours job to do it right.
 
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