Why do oversized PV covers do what they do?

[motogroove]

People are changing their power delivery using the oversized covers. Better low end I believe is the goal.

The action of the rotary valves that (I think) port the exhaust over into the PV cover(s) is kind of hidden, and I'm trying to understand the how and why.

When is the PV chamber in use? High revs or low?

My crude understanding is that the PV chamber volume is used sort of like stretching the exhaust like a trombone. But I could be way off and I still don't quite get the timing, etc.

Anybody want to take a crack at explaining it?

Thanks a bunch!

[noobi]

They work to boost bottom end response by increasing the resonating volume of the exhaust, I think?. They are only in effect when the PV is closed, when the PV opens at higher revs that area is blocked so no longer effects. It gives the bonus of adding length to the pipe for bottom end advantages with out the disadvantages of a longer pipe, which is obviously harder to make fit on the bike.

Someone else will have to chime in on the mechanics of it, I havent covered that part of my degree yet

[GMP]

Thats basically it. The left side drum valve in the PV is like a two position valve. At lower RPM, the exhaust sub port is open to the chamber formed by the cyl and PV cover. At higher RPM, the drum rotates and closes off this chamber as it opens directly to the main port/header.

The PV cover has more effect on the 200s and 250s than the 300s, and also more effect if you are running a mid to top end orientated pipe. I like how it works on a newer 250. With this, a head mod, and good jetting, it will pull from a crawl at idle to a screaming top end. An older 300 with an old Gnarly pipe will not benefit or need a high volume PV cover.

[HuskyDude]

Ya...what they said.

I have one on my 2010 300. I tried it with and without and I think it does have a positive effect at really low rpms. The bike doesn't stall as much and pulls real hard from a almost dead engine. Great for tight S/T, logs and stuff.

[bchatt]

OK, thanks for those explanations, I understand what you are saying but I have a question. I have been wondering why the actual volume of that left chamber is so important, and why the increase in volume gained by the addition of the larger PV cover has the effect that it does. I have made a 10mm spacer, and found it made no difference. The aftermarket covers all seem to be about 20mm. What's the significance of this volume and why don't the engine designers get it "right"? How did they come up with the volume that they did?

[wasp4banger]

Originally Posted by bchatt

OK, thanks for those explanations, I understand what you are saying but I have a question. I have been wondering why the actual volume of that left chamber is so important, and why the increase in volume gained by the addition of the larger PV cover has the effect that it does. I have made a 10mm spacer, and found it made no difference. The aftermarket covers all seem to be about 20mm. What's the significance of this volume and why don't the engine designers get it "right"? How did they come up with the volume that they did?

When you say how don't they get it right, any design is at best a compromise. We all ride with different styles over different terrain with differing levels of ability. The factory set up is a good starting point, most who know how to ride, set their bikes up to suit their own needs.
I wanted more bottom end tractor like power, so added a large volume PV cover, and reduced the base gasket thickness and jetted to suit. The bike is now awesome off bottom and no slouch at wide open throttle. My mate with a KTM 300 wishes his bike pulled like mine off bottom.

[husley]

Originally Posted by HuskyDude

Ya...what they said.

I have one on my 2010 300. I tried it with and without and I think it does have a positive effect at really low rpms. The bike doesn't stall as much and pulls real hard from a almost dead engine. Great for tight S/T, logs and stuff.

Exactly what I wanted to hear...........which cover did you purchase?

thanks!

J

[HuskyDude]

Originally Posted by husley

Exactly what I wanted to hear...........which cover did you purchase? thanks! J

[GasGasDreamer]

Originally Posted by GMP

An older 300 with an old Gnarly pipe will not benefit or need a high volume PV cover.

IMHO, I added the PV cover and loved what it did for my '06 300 bottom end.
I tend to take the enduro where trials ride so maybe that has something to do with it too.

[kyle]

Originally Posted by Elvis74

I just like to know everybody that I ordered new spacer plates for the PV and they will be ready in about 2 weeks.
They are 15mm and come with gaskets and screws.
I will sell them for 33,- euros including international shipping.
I am not a dealer, I am just having fun of doing things like this.

If anybody wants one, please send me private message.

Just got elvis74 spacer. His product and sevice would put big dealers to shame. Excellent . Many thanks.!!!

my fingsers are tio fat fir the keypad