POwervalve question

[LapTraffic]

Sorry if this is a stupid question, but what is a powervalve and what does it do for the engine? Is it something that would benefit any 2 stroke, like a banshee or is it primarily used on 250r's?

Thanks!

[SBC101]

This should help read this.
One of the challenges of designing a high-performance two-stroke power plant is finding the right combination of peak horsepower and useable power. Two-stroke engines that develop a lot of power tend to have that power focussed around a narrow rpm range. If the engine's application required that it run at a constant rpm the entire time it is in operation, useable power wouldn't be such a concern. In the situation where the two-stroke engine is the power plant in a vehicle, a careful design compromise must take place if the operator is to accelerate to cruising speeds.

Many high-performance two-stroke engines are equipped with a feature that broadens the useable power range. This feature is more commonly identified by its generic name: "power valve". The ultimate goal of a power valve is to make the engine's power more useable by broadening the useable power range while affording the designer higher peak power levels at less of a compromise.

Here are some of the various power valve technologies used by two-stroke engine manufacturers:

SAEC Suzuki Automatic Exhaust Control
ATAC Automatic Torque Amplification Chamber (Honda)
KIPS Kawasaki Integrated Powervalve System
YPVS Yamaha Power Valve System
HPP Honda
EEMS Electronic Exhaust Management System (Polaris)
AETC (Suzuki)
There are two main types of power valve designs. One type modifies the volume of the exhaust pipe's tuned chamber (i.e. SAEC, ATAC). The other type is generalized as "exhaust port modifiers". Exhaust Port Modifiers varies the exhaust port timing in the cylinder (i.e. YPVS, HPP, RAVE) in one fashion or another. I say "one fashion or another" since KIPS is technically different than the others in that it open and closes auxiliary exhaust ports where as HPP and RAVE simply raise and lower the top edge of the exhaust port. One thing that is common to all of these technologies is that they actuate, ideally, in response to engine rpm and throttle position to a lesser extent.

The presence of this feature doesn't, in itself, increase peak power, but it allows the porting design and exhaust pipe shape to be more focussed on providing the greatest amount of peak power, relying on the SAEC chamber to return the low rpm power that is often lost on high peak power porting designs.

[LapTraffic]

lol
freaking perfect!

So on a 250r does it come with a powervalve or is it added later? What are its drawbacks?

do they do the same thing with a banshee motor? are the effects similar?

Thanks!

250rs didnt come with a powervalve they have to be installed. Also it gives much better low end

[wilkin250r]

Try doing a search. This question comes up alot, and many people (including myself) have written responses on the technical aspects of powervalves.

As I'm sure you know, two strokes don't have valves like a four-stroke. The timing is based on the hieght of the intake and exhaust ports. Doing port work on a two-stroke is just like adding a high performance camshaft in a four-stroke.

Exhaust gets pushed out by a fresh new fuel/air mixture, but some of that new fuel/air also exits the exhaust port. Imagine if you could vacuum out the old exhaust, but when your new fuel/air mixture starts coming out your exhaust, you can suddenly increase the back pressure so that you don't lose any of your new fuel/air mixture. This is exactly what a tuned pipe does, it creates a sound wave that will create a vacuum and back pressure at exactly the right moment. However, the sound wave with the exactly length at timing is only produces by a certain rpm. This is what creates that "two-stroke powerband" because this is the rpm that will produce a dramatic increase in power because the sound wave will produce an increase in back-pressure and the exact time the new fuel/air mixture is trying to escape out the exhaust port.

A powervalve creates variable valve timing by raising and lowering the height of the exhaust port. This allows the engine to produce great low-end torque because the exhaust port is smaller, so it can build more compression. But when the rpms rise, so does the exhaust port, so you can take full advantage of your pipe and top-end power.

Most of the time, you can either have great low-end power and torque, or top-end horsepower, but you can't have both. A powervalve will give you both, it's the best of both worlds.

[LapTraffic]

Thanks for the reply and I'll do a search on the subject.

One last question since i doubt I'll find it in my search on this forum. I hear about Powervalves in 250r's, but not in banshee motors. Is the benfit less in a banshee? Just curious.

Thanks

[lilmxe#43]

if ur goin to put in a power valve, try to get a top end pipe, a pipe that benefits top end power,that way u will have extreme top and a braod low end. Have done this on many 250r's and works like a dream!!!

[wilkin250r]

Originally posted by LapTraffic
Thanks for the reply and I'll do a search on the subject.

One last question since i doubt I'll find it in my search on this forum. I hear about Powervalves in 250r's, but not in banshee motors. Is the benfit less in a banshee? Just curious.

Thanks

Yes, there are banshee powervalve kits out there, try doing a web search. I think LRD and a few others have powervalve kits for the banshee.