Here is my situation. My bike (1990 CBR600F) already has a Vance and Hines SS2-R slip-on installed with the factory header. I recently purchased a never used Yosimura header from ebay. This is the same header used with the old Yoshi systems made back in the day for the Hurricanes. My plan is to bolt on this header while using my SS2-R slip-on and the chrome midpipe that came with it. In order to make this system work, I need to fab up a short piece of pipe because the new header exits underneath bike while the old header exited under the right hand side of the bike. The collecter on the new header hasa 2' OD which means I can use pre-bent pieces of exhaust pipe from any parts store. The only thing that concerns me are the crimp bends in the pipe itself. BUT here's something interesting. A mild built Chevy 350 will flow 2.25' pipe without any restriction. My 598 cc engine is only 36.5 cubic inches. It would take roughly 10 cylinders from my bike to equal that of a 350. SO regardless if I decide to use these crimp bent pieces, they should still flow adequatly for my relatively stock engine. To make this work I'm only going to need 2 30 degree pieces to make the system fit together. Just eyeballing those 30 degree pieces, the diameter doesn't look to uncheanged but like I said im only flowing 37 cubic inches. What are your thoughts for a situation like this?

 

if you aren't racing or trying every last horsepower trick, i wouldn't worry about it. if you've ever looked on the inside of exhuasts put together after welding, there is plenty worse then crimps - weld slag, pipe ends that weren't dressed or reamed clean, poor alignment, etc. and oem pipes that are mig welded are the worst becuase there is very little prep and not a whole lot of skill. you would find a lot of manufacturing no-no's in there.

as for flow, you aren't restricting it, so i wouldn't worry.

 

I would imagine it would still flow better then the OEM header did.

 

well, if you wanted better flow, just run straight pipe or ditch the whole exhaust system, headers all the way back. it'll probably save you 30lbs in the process.

 

I was comparing the old and new header. Of course an open exhuast flows the best but then you run into legal issues.