EXUP

EXUP (EXhaust Ultimate Power valve) is a device fitted to selected Yamaha motorcycles (FZR,YZF,XV1900,R series) that constantly adjusts the back pressure within the collector of the exhaust system to enhance pressure wave formation as a function of engine rpm. This ensures good low to mid-range performance.

At low engine speeds the wave pressure within the pipe network is low and hence to increase low RPM torque large amplitude exhaust pressure waves are artificially induced. This is achieved by partial closing of an internal valve within the exhaust (EXUP valve) at the point where the four primary pipes from the cylinders join. This junction point essentially behaves as an artificial atmosphere, hence the alteration of the pressure at this point controls the behavior of reflected waves at this sudden increase in area discontinuity. Closing the valve increases the local pressure, hence inducing the formation of larger amplitude negative reflected expansion waves. This thus enhances low speed torque up to an RPM where the loss due to increased back pressure outweighs the EXUP tuning effect. At higher RPMs the EXUP valve is fully opened and the exhaust is allowed to flow freely.

A full description of the process can be found on the exhaust manifold page. A servo motor controlled by the ECU opens and shuts the valve. The EXUP valve operation goes from being almost fully closed at idle speed, through to being fully open at 9000 to 11000 RPM (2500 RPM for XV1900).