These pipes are small diameter 1 1/2".... I guess back in the day, the factory felt the K Model 750cc side valves worked best with these smaller diameter headers? Similar sized to the ports, etc. I always like the big, free flowing straight pipes, but so far, this thing seems extra responsive and hopefully it will help bring back some low end to this thing . . ? Factory stock early Sportster muffler. It's got a set of -60R KR heads on it, and I resleeved the cylinders, new valves, guides, etc. The Delorto PHM38 is my new carb-of-choice (if you don't want to run an M53 Linkert). I haven't really rode it around yet, so I'm sure I'll have some tuning issues coming up. Hopefully not - is always nice ! I added my set of -60 aluminum wheels (I'd been saving for who know what?) and figured I may as well start using some of this stuff.... One thing is for sure, H-D made some pretty neat bikes back with the Ks and early Sportsters. Some of the neatest lookin' if done right.