A few questions...

[400EX QUADER]

I always see stuff about power valves and I was wondering what they are compares to regular cylinders??
http://www.esr250.com/power_valve_cylinders.htm
also whats the best size to do for the oregon dunes and still bein farely reliable? also what would the best pipe out of these to use with it?
http://www.esr250.com/250r_pipes.htm#trx6 and would a pwk 39mm airstyker be good for it? Any other mods ya wanna do with it? what would the hp numbers be? I might get a 250r within the next year or so and was wondering. And can ya tell me about the reliability of these/performance..
thanx

[wilkin250r]

First off, you need to understand exactly how these 2-stroke motors run, and how they are different from 4-stroke motors. The port timing, and how the expansion chamber (exhaust pipe) helps build power.

A powervalve helps give a little more low-end power at low RPMs, and then high-end power at high RPMs. It does this by altering the height of the exhaust port as RPM changes. It gives a very smooth powerband.

That smooth powerband is extremely important in racing, because you don't have that hard "hit" that causes the wheels to break traction. You get much better hook-up and better lap times.

However, there's nothing in the world that can prevent wheelspin in the dunes. It's sand, it's impossible to have great traction, even with the best paddle tires. That's why (in my opinion) powervavles are almost useless in the dunes. In fact, I would take a non-powervalve for the dunes any day, because I want that hit, that burst of acceleration. I love it.

[400EX QUADER]

ok sweet! whats a good pipe for like a 270 or 290 kit? trx5 centerpipe?

[wilkin250r]

TRX5 is a decent pipe, but take a step back and think about the bigger picture.

Why are there different pipes on the market? If there was one "best" pipe, wouldn't we all be using it? Then how would any other pipes sell, if everybody is only buying and using only the "best" pipe?

Pipes are different, and they each have different characteristics. The "best" pipe isn't an ESR or a CT Rcing pipe. The best pipe is the one that gives you the power characteristics you want, the one that works best for your particular riding style. Some people like low-end power, some want all-around power, others like peak HP in the high revs.