I just bought an HMF Penland Pro (utility series) race muffler w/quiet core and jet kit for my stock 650 Prarie 4x4. Anybody have any clue as to how much horsepower and torque I'll gain? As it is now, The book states I have 42hp @ 6500 rpm and 38 ft-lb of torque. The original main Jets are #'s 138 (front) and 142 (rear). The new HMF main jets are #'s 142 (front) and 145 (rear).

 

Probably 5hp or less. An exhaust alone wont give you all that much. If you havn't try a new CDI. I've ran the dyna on everything from my stock motor to my 730 and have never had any trouble.

 

What about with the new jet kit? what will that add?

 

With a pipe, jetting, filter and snorkel, a CDI, and some new clutch springs, mine would run dead even with a 2005 brute force, which has 51 hp. I would say the pipe and jets are around 4-5 hp. Get a CDI for another 4-5 hp and you will be getting somewhere. Just don't expect to outrun 800 bombs and renegades, cause it won't happen.