The valve typically is spring loaded so if disconnected it will hold the valve in the full open position. It can be accomplished as easily as removing the cables that connect the valve to the motor. Removing or bypassing the valve is quite easy. The exhaust valve system is typically replaced for several reasons including the installation of an aftermarket exhaust that does not have the valve (most full systems and some slip-on exhausts), the valve or servo motor fails and needs to be replaced or removed, or the owner just wants a little more power. Why should I eliminate the exhaust servo motor? Additionally, in the USA, most bikes close the valve again at the upper RPM range, but in Europe they do not (different regulations) and the European bikes typically create a few more HP on the top end as a result. The proof of this has been shown on the dyno where removing the valves and retuning the engine creates a flatter better torque curve. The exhaust valves are partially closed at idle and low rpm to reduce noise, and closed again at the upper RPMs to meet peak noise regulations.
Unfortunately, this probably isn’t the real reason the true purpose of the exup valves is to meet noise regulations. The purpose of this system according to the motorcycle manufacturers’ marketing departments is to create back-pressure at lower RPM’s to increase torque.
The cables are used to isolate the motor from the hot exhaust and allow it to be placed in a more convenient place on the bike. This motor, which is controlled by the engine control unit, has a pulley on top that rotates the cables to open and close the valve in the exhaust. Connected to this valve is a set of cables that run to the other part of the system, the servo motor. This is a simple butterfly valve that can open or close to change the amount of exhaust flow. The system consist of a few parts, the first is the valve assembly inside the exhaust pipe. Exhaust valves and servo motors explained What does an exhaust servo motor do?Īn exhaust servo motor is one component of the exhaust valve system (sometimes called the ex-up or power valve system) found on almost every modern sportbike including all Honda, Kawasaki, Yamaha, Suzuki, BMW, Ducati, Triumph and a few others.
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