Powervalve Question(s)

[WD-fourD]

First of all what exactly does a powervalve do? I'm pretty sure it smoothes out the powerband, right?
Second, when were they introduced? I know that 80's didnt have them until 1999 or so. What about 125's and 250's?
I am asking this because I am thinking about buying an older model (mid 90's) 125, and don't know if a bike with a powervalve will be any different from a bike without one. Any help would be appreciated.

 

[kawamaha]

without a powervalve you have to decide, do i want power low to mid, or mid to high rpm? of course, every bike has mid to high. 1983 (or earlier) Yamaha introduced the YPVS, 1986 Honda came out with the HPP on the CR250 (the ATAC is not so effektive). 1987 i think Kawasaki followed with the KIPS. all systems increased the power from low to mid without decrease the high rpm power

 

[i_955]

A valve of any kind is a device that restricts flow.
In an exhaust port it is closed (not completely of coarse) during low pressure, or low RPM. As the rpm increases the valve is forced open by the air pressure (or other mechanical means) until it is fully open at max RPM.

While the exhaust valve is closed at low RPM it generates back pressure which aids in the engines ability to expel the burnt exhaust gases efficiently.
The end effect is a more controlled burn at lower RPM, giving a more usable spread of power or less of a “hit” when the motor finally gets on the tuned pipe.

I personally would search for a bike with a power valve. But I’d search for a bike with modern suspension long before I’d dode up for a power valve equipped on. Unfortunately all modern suspension equipped bikes come with power valves.

I think that is mostly correct. :cool:

Good luck.

 

[2-Strokes 4-ever]

If you've ever ridden an early model Honda Elsinore, you'd know the benefits of power valves and reed valves. Those bikes were screamers, but no low-end at all! Use the "search thread" button for more info...power valve cleaning, adjusting, etc...

 

[bikepilot]

It simply varies the port size/shape/timing based on engine rpm, allowing it to be closer to optimal for a wider range of rpm's.

I don't think there's been a MX 125 or 125 without powervalves since the mid 1980's. I know that by the 1990's they all had powervalves. No need to worry there.

 

[WD-fourD]

OK thanks everyone. Thats what I needed to know