Yoshimura R-77 Slip-On Exhaust | 15002B0520. The BMW R 1250 GS is a beautiful adventure machine that claims 136HP and 105 ft. pounds of torque in stock form. We decided to add to the excitement of the 1250 boxer engine.Using our Works Finish R-77 profile muffler we developed a slip-on that adds 1.4 % peak HP and 1.5% peak torque. These improvements not only make this beautiful BMW more fun to ride, our R-77 makes it rumble- Yoshimura R-77 Slip-On Exhaust | 15002B0520.