Four-stroke power valve system

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The exhaust power valve of a 2007 Honda CBR600RR.

The servo motor controls the valve via two cables. Shown removed.

A four-stroke power valve is a device fitted to four-stroke engines that constantly adjusts the internal diameter of the exhaust system to better suit the speed of the engine. Yamaha was the first to develop such a system, called the Exhaust Ultimate Power Valve (EXUP).^[1] It first appeared on the Yamaha FZR EXUP and was later used on many other Yamahas.

Later versions from Honda went by the names Honda Titanium Exhaust Valve (HTEV) and Honda Variable Intake/Exhaust (H-VIX),^[1] appearing on the CBR600RR and Honda CBR929RR. Suzuki's version is called Suzuki Exhaust Tuning (SET).^[1] The system is also used on the Triumph Daytona 675 triple.