Yoshimura R77 Slip Ons

[Huls]

I've always been told that by removing the stock exhaust on any bike and replacing it with a freer flowing system will impact upon torque, power and air/fuel ratios. Stock exhausts are fitted with lost of baffles etc to reduce noise, emissions and this obviously slows down exhaust gases exiting. The back pressure from the stock system helps with torque which is why Yamaha patented their EXUP exhaust valves years ago. The EXUP valve would be in place below say 5000rpm to assist with noise, emissions and torque, then rotate out of the way as revs rise in order to take advantage of freer flowing exhaust gases as faster exiting gases assist with improving engine performance. By fitting R77's you have achieved the same things. Downsides are loss of back pressure and therefore torque at lower revs and potential changes in air/fuel ratio causing flatspots and leaner/richer running at certain revs. Change the air filter to a K & N or similar and get the bike dynoed to take advantage of the changes you've made.