doesn't the viper have a detuned srx engine? i'd check that out with a dealer or on ty forum (totally yamaha). maybe you can use the stock triple pipes from a srx. with that said....
SLP claims 33hp+ w/ their pipes
Yamaha - 700 Viper Triple Pipes - Starting Line Products
SLP trail porting for the Viper in conjunction w/ their triple pipes will give you 160hp
Yamaha - Viper Trail Porting - Starting Line Products
just start looking around, i really suggest the ty forum. my buddy has a 98 srx and has found amazing deals on the forum. people with massive knowledge and parts (like here) but only yamaha.
