Header Diameters

[XSWestgate]

I've started getting parts for an exhaust system to replace the old welded special ones. The headers are about as far as I could get before running into uncertainty where to go next. The headers are the ones with bend on the lower section. The odd thing is, when i'm shopping around for mufflers they quote either 45, 42, 38, or 35 mm and mine seem to be right in the middle at 40 mm. the muffler i'm currently considering is the taper tip from xs650direct which quotes a fit on the 45mm or 38mm headers. My concern is that i'll buy something and have to hack at it to make it to half-a**ed fit. i'll head home and take more measurements but wanted to see what input this group has.

Aside from that, I'm considering a custom setup with straight pipes and the homemade baffles as well.

What do you guys think? Thanks for your input.

 

[aldo5468]

I've started getting parts for an exhaust system to replace the old welded special ones. The headers are about as far as I could get before running into uncertainty where to go next. The headers are the ones with bend on the lower section. The odd thing is, when i'm shopping around for mufflers they quote either 45, 42, 38, or 35 mm and mine seem to be right in the middle at 40 mm. the muffler i'm currently considering is the taper tip from xs650direct which quotes a fit on the 45mm or 38mm headers. My concern is that i'll buy something and have to hack at it to make it to half-a**ed fit. i'll head home and take more measurements but wanted to see what input this group has.

Aside from that, I'm considering a custom setup with straight pipes and the homemade baffles as well.

What do you guys think? Thanks for your input.

1 1/2" OD is a common diameter for aftermarket pipes for our 650's - that is 38mm. 45mm is 1 3/4" OD, which is too large for the exhaust gas volume coming from a 325cc cylinder.

 

[5twins]

Large diameter pipes only make good power at very high RPMs, like near, at, or above red line. Maybe that's OK on a race bike, but not too practical on a street bike. Also, they make less power in the low and midrange RPMs than a smaller diameter pipe. As mentioned, 1.5" is the accepted norm for a good replacement pipe. It's slightly larger than the original about 1.25" pipe, but not too big. The originals are rather restrictive but the first couple inches up at the head are good like that. If you're going to build your own header pipes, you might consider using the first couple inches off your old stock pipes and weld your new slightly larger pipe to that. That will give you the nice fitting flange for sealing purposes and the smaller I.D. for the first few inches that this motor likes.