The difference is the race version has a larger muffler baffle tube and end cap. The standard has a 2" opening with spark arrestor, the race is 2 1/4" and has no spark arrestor (although you could add one). The larger opening increases power and torque but makes it a bit louder. Either version needs to be repacked periodically but I believe the race version doesn't have as much space for packing so this needs to be done more often. XRO has had at least three vendors making their pipes over the years so there are many variations. For example, some have two-piece headers while others have three, and some go straight across the front of the frame and some taper inwards on the right side of the bike. Tightness of fit also varies. Obviously you don't want any air leaks from a sloppy fit so I'd be looking for some extreme temp silicone to fill any voids. The header isn't designed for clamps. Speaking of air leaks, it's a good idea never to reuse the round head exhaust gaskets...they need to be replaced every time.