slightly off course and ive asked this before, do any of think their is any performance to be gained by redesigning the muffler  portion and going to a center style mount? ive seen lots of trx guys run a center mount style rear muffler portion that slightly shortens the total length and has a straighter shoot out vs bending the pipe to go around the frame to clear the factory air box. most high hp builds do not run an air box so why design a pipe to clear a part that isnt used??? on the pic from the first posts, looks like their are unnecessary bends to clear an air box that isnt there.

The center mount pipes that ESR makes reduces the back pressure a little on the TRX5, TRX9 and TRX11 pipes.  The tubing bender that ESR uses to make their out of frame silencers and stingers crushes the bends about .100".  The extra bends in the stinger and the crushed bends limits you to about 50 hp before you start to have piston overheating on the above mentioned out of frame pipes.

The center mount pipes allow one to make a little more power power before running into the same problem.  When you try to push  over 55 hp of exhaust through the center mount exhaust on the big bore engines (310s, 330s, 350s, 370s,) we are still seeing piston overheating due to to much back pressure.  Pipe restriction is a function of HP. 

We have solved the piston overheating problem on the ESR pipes by making larger stingers and silencers for engines over 55hp