What exactly is a powervalve? What does it do? How much horsepower do you gain by having one? I have seen them on some bikes and wonder if they are worth the money. Is there anything that can go wrong with them? Thanks for the help.

 

It's complicated in a simple way. Basically, a powervalve is a device used to change exhaust port timing in 2 stroke engines. On most models, it is a cylinder with a concave cutout on the side. When the valve is rotated to make the port smaller, it is the same as having a pipe made for torque. It makes the gas "waves" come into the cylinder with less force. When it is turned to open the port fully, it is like having a top end pipe. It allows the gas waves to return with more force. Other types of powervalves are the sliding "guiltine"(sp?), which is a flat plate that slides up and down.

On modern dirtbikes, it is actuated by a linkage connected to the crank and varies with engine rpm. Some models use a servo motor run off the electrical system and controlled by a tiny computer.

You can't just add a powervalve, it must be built into the cylinder because it requires a hole to be cast into the cylinder so the valve can be as close to the sleeve as possible, so it makes the biggest impact in power.

Not alot can go wrong with them other than being clogged by gummy buildup caused by poor quility pre-mix. That's why many companies advertise their oil to be non powervalve clogging.

The power added is hard to compare because manufacturers don't usually offer powervalve and non-powervalve models. I can give you some sort of idea though: I am building a liquid-cooled, powervalved blaster. A stock blaster makes roughly 17hp. With the liquid cooling and a powervalve, it skyrockets to 30hp. If that cylinder didn't have a powervalve, but was still liquid cooled, it would still make probly 23-26hp. The powervalve does more for the torque numbers than horsepower.

I am not an expert engine builder, but this info I have given you is what I see when I look for info on the subject. I may have put in the wrong terms here and there, but I think I pretty much explained the basics.

 

Thanks for the help. That was an excellent answer. I knew a little bit about them but you answered all the questions that i had. Thanks again for the help.

 

I just wanted to add a bit to what dirt817 had to say. A regular Blaster cylinder could be ported (in theory, don't flame me if there is not enough material or something) to yield the same peak HP as the power valve cylinder. However, that motor would have no low end torque. The power valve cylinder will likely also make higher peak torque because with the valve in the down position (sliding plate type) the exhaust port roof is probably lower than the stock cylinder. Without a power valve, you port for a happy medium between top end and low end. With a power valve, you can have both.

The Rotax twin in my Drakart has power valves that Rotax calls RAVE.