Powervalving???

[Nightbiker07]

ok....this one has me stumped.
i know, with complete ann total understanding of the mechanical workings of 2 and 4 stroke engines.....but this mod has me stumped....
it is something done to a 2 stroke, correct?
how, in jesus name, do you powervalve a 2 stroke? will someone explain the mechanics of this mod? cause 2 strokes dont have valves.......

[Tyler]

A powervalve is used to change the height of the exhaust port. The higher an exhaust port the better the top end. Think of exhaust port height as like cam duration on a four stroke. The ports shape (width and height) determine the powerband by altering the timeing of exhaust and reversion (from the expansion chamber) which helps bring in a fresh intake charge. The powervalve is simply a a valve that opens and closes the exhaust port to alter the shape of the exhaust port. It is timed by rpm as to how much the valve opens and closes.

[Nightbiker07]

ah i see. i guess lol. so is there an actual moving assembly, or is it just changing the exhaust port in the cylinder wall?

[McDerry]

In addition there are other systems, like the old honda ATAC. On the ATAC it opens a butterfly valve in the exhaust manifold allowing the escaping exhaust charge to enter into a additional chamber. This increases the size of the expansion chamber and artificially increases the length of the exhaust chamber (sound waves/ exhaust pulses follow along the outside surface of the exhaust in addition to moving through the fluid medium aka air). Inturn you gain the benefits of a large pipe, in addition to controlling the timing on the reversion.

[McDerry]

Heres a linky to show yah how the powervalve adjust the port sizing (http://www.dansmc.com/powervalve.htm)

[GoodKarma]

If the technical stuff doesn't make sense, think of it like this: There's a part that sits right at the exhaust port, the powervalve. This part is a cylinder with a flat spot, sort of. Anywho, when the motor is at lower rpm's, the powervalve is closing off the exhaust port. When higher rpm's are reached, the powervalve is rotated to open up the exhaust port. So this is where that flat spot moves to allow the exhaust pressure out at high rpm's.

I guess it's not that easy to explain, but if you see one up close, it seems pretty simple really!

[cr480r]

There has been many different exhaust valve designs used over the years by manufacturers.. But they all are trying to do the same thing... and that is to make a broader powerband... A powervalve doesnt make horsepower... it just allows the power to made without sacrificing the low-end performance... The best of both worlds is the goal... Some designs alter exhaust port timing... others open and close auxiliary ports... and some alter the tuned effect of the pipe by opening and closing resonance chambers...

[Nightbiker07]

ah i understand now, i guess.
i would have to see it to completely grasp the concept, but i ave a good idea now !

[tecat-z]

Seems Yamaha has almost always used the power valve to alter exhaust port timing, while kawasaki used valves to open and close auxilary exhaust ports, at least on the Tecates. Never understood how 250 and 500 quadracers exhaust valve worked. Yamaha always semed to have the most straight forward and time tested design. While other oem's were changing designs many times during the 20 plus years powervalves were being used to find the 'perfect balance' of power.

[factoryX]

post pics please..!!

[cr480r]

Never understood how 250 and 500 quadracers exhaust valve worked.

Thats because they hardly even do.. lol... Most suzuki riders cant even tell when the valve gets stuck or the the linkage fall apart...

[factoryX]

well that is because suzuki has always had motor problems...