This listing is for a TSP oversized powervalve cover to suit all 250 & 300 23-on TBI models. This includes SX, XC, EXC and XC-W models. The cover will work with stock or aftermarket pipes.

This cover will not only enhance the aesthetics of your bike, but it adds power at low throttle and low/mid revs where most riders need it most! It is ideally suited to trail riders and hard enduro riders who want smooth power delivery and maximum torque at low revs, before the powervalve opens.

Our TBI Oversize Powervalve Cover is not just bling! Its been carefully designed and tested to ensure noticeable gains at low/mid revs. It is most effective between 3000-5000 and at low throttle, adding a torquier feel to the power delivery.

Check out the dyno results on our 2024 KTM300EXC TBI shop bike. This bike is running a Medium Compression TSP head with a TSP ECU tune. Adding the Oversize Powervalve Cover further increased hp and torque down low by a noticeable amount.

Dont be fooled by cheap bling covers on the market, they are not the same product as our TSP Oversize Powervalve Cover!

How does it work?? 

At high revs the pressure waves travelling back and forth through the expansion chamber help to supercharge the cylinder, filling it with more fresh fuel/air than it would otherwise receive. This supercharging effect, and the extra power that results, is often what riders feel when they say a 2 stroke is “on the pipe” at higher revs.

The downside of this phenomenon is that the same pressure waves that help to supercharge the cylinder at high revs actually make it harder for fresh charge to enter the cylinder at lower revs. This causes a drop in power at low/mid revs. To combat this some powervalve systems incorporate a ‘Torque Chamber’. A Torque Chamber is a chamber on the side or top of the cylinder which is opened and closed by the action of the powervalve. When the powervalve is closed or down, the chamber is open to the exhaust gasses. When the powervalve opens at high revs the chamber becomes closed to the exhaust gasses.

At low revs, when the chamber is open, the pressure waves travelling through the expansion chamber enter the Torque Chamber and are dissipated somewhat, losing some of their strength. The reduction in the strength of these waves helps to improve the filling of the cylinder with fresh charge. Therefore, the Torque Chamber adds extra power down low by reducing the negative impact of the pipe in this rpm range. By adjusting the volume of the Torque Chamber we can further reduce the negative impact of the pipe at low revs, and increase power even more. This is how the TSP Oversize Powervalve cover helps to increase power at low revs (approx 3000-5000rpm).

In order to find the ideal volume of the chamber we spent months dyno and track testing various designs until we settled on a design that made a noticeable improvement in low/mid torque.