powervalve??

[cudaman]

i know this is a newb question but what is the difference between pv and normal. i think i know i just want to make sure. please dont flame me too much lol.

[4TraxRider]

A powervalve basically closes the exhaust ports smaller, so taht you can produce more low end, and at higher RPM it opens and produces more topend.

[wilkin250r]

Originally posted by 4TraxRider
A powervalve basically closes the exhaust ports smaller, so taht you can produce more low end, and at higher RPM it opens and produces more topend.

Exactly. Two strokes don't have camshafts to adjust valve timing, the timing is based on the location of the intake and exhaust ports.

I'll give you a general guide by looking at the two extremes. When the exhaust port is really low (small hole) then you get more compression in the cylinder, which is great for the low-end of your RPM range. The problem is, when you get into the higher RPM range, you have more restriction to exhaust, which results in less peak power (because peak power is almost always at high RPM)

When you have a tall exhaust port, you don't build very much compression at low RPMs, so you don't get much power. However, with less exhaust restriction, you get GREAT power in the upper RPM range. This results in a higher peak power, but it gives it that "light switch" feel, you either have no power, or you are all balls out...

The powervalve changes the exhaust port based on exhaust pressure (which increases with RPM) so that you have a small port at low rpms, giving you great low-end power, and then will raise the exhaust port at high rpms, giving you great top-end power without the "light switch" feel.

This is a general guide of only one aspect. There are other factors involved. Overall compression ratio, tuned exhuast pipes, port design, and reeds all play a big part in power output and shaping the power curve, each of them can be more important than the exhaust port.

[KASCHAK]

hey how much does the powervalves run hard to install or is it just valves?

[wilkin250r]

You can't just "add" a powervalve, it has to be integrated into the cylinder. The only way to do it is to completely replace your top end with a powervalve setup. It will usually run about $1500-$2000, but it isn't any more difficult than a top-end rebuild. It can get more expensive than that, depending on what you want to do, upgrade the clutch, heavy-duty rod, machine the cases for a big bore...