Well I was getting ready to pull my motor to install the 350cc big bore kit so I could degree the new cams in to make sure everything is good and get it back up to the dyno, but then I seen how small the pipe was inside the first inch of the pipe. It necks down to a 1 inch pipe inside, it looks big enough on the out side but it's a double wall pipe. I would have liked to used 1 3/8th O.D. pipe that the aftermarket pipes would be, but I only have 1 1/2 O.D. so I built it with that the first part, then jump it up to 1 5/8th into a little bigger back to a Muzzys muffler I had sitting around. We ran 1 1/2 pipes on the 200x for years so I think it will be OK.