Exhaust ultimate power valve

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The exhaust ultimate power valve (EXUP) 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 speed. This ensures good low to mid-range performance.

At low engine speeds the wave pressure within the pipe network is low. A full oscillation of the Helmholtz resonance occurs before the exhaust valve is closed, and to increase low-speed torque, large amplitude exhaust pressure waves are artificially induced. This is achieved by partial closing of an internal valve within the exhaust — the EXUP valve — at the point where the four primary pipes from the cylinders join. This junction point essentially behaves as an artificial atmosphere. 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, inducing the formation of larger amplitude negative reflected expansion waves. 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).

See Also

Exhaust manifold