What does the PV chamber do?

[stay_upright]

Could some-one explain how the PV cover/chamber on the LH side of the engine works

Also what is the idea behind the two additional rotary PV 'valves'

 

[socalscott]

Could some-one explain how the PV cover/chamber on the LH side of the engine works

The left rotary PV when closed(hi compression) diverts exhaust to the
chamber. Effectively creating a larger volume head pipe segment.

Also what is the idea behind the two additional rotary PV 'valves'

Wider port area. They provide hi-compression up to mid rpm and lo-compression from mid on up. There's an ideal point for them to open. It's where hp can take over just as bhp peaks. We can play with that point with
PV gov. spring pre-load or different spring rates.

 

[mountain thumper]

are you saying you can "tune" the pv

 

[JoshP]

Thrusty does make a tunable PV cover for the euro's. With some fancy on the fly tuning dial. Almost seems like cheating.

 

[Skidad]

Thrusty adjustable power valve

http://www.trialendurodirect.com/products/15_17/Adjustable_Powervalve_Cover_139.html

Also see the pics I posted above for this.


Skidad in MA

 

[JoshP]

Now all your need is the GasGas Skidad. Sorry had to say it.

 

[nhrider]

Now all your need is the GasGas Skidad. Sorry had to say it.

He's trying! Skidad, don't worry something will come up...

 

[asshat]

Adjustable pv's rock.

I just bought an 2002 xc 250 in close to mint shape, around 25 hrs. But my older ride is a ATK lq 260 with a Rotax in it.
The rotax used has an adjustable power valve. I must say it is one of the cooler things about the bike. The engine is great. Not a powerhouse but for my lightweight, it goes well. Ultimately reliable. In the spring I crank the PV spring tension tighter to open later, and its electric. As it dries towards summer I set it mid depending on traction required, if it's hard, I just set her to open earlier.
Why they all don't do this I have no Idea. Sounds like a decent way to take the edge off of those XC's,DE's and MC's people out here in the East are running. Cheaper than an expanded pv cover/Throttle Cam/Flywheel weight/ EC ignition combo. And once installed way easier to go back and forth. Simply bend over and crank the screw.
Anyone running one? How easy to install?

I am asshat

 

[stay_upright]

So the chamber (LHS cover) acts as sort of a mini expansion pipe then?

i.e. exhaust gas goes in - reflects off a surface and is pushed back into the cylinder?

 

[2 strokes 4 life]

They way i look at it is Vboost like on a Yamaha Vmax almost. It opens after a serten amount of exhaust gasses that pass through it and then it whacks open and lets more exhaust out.

 

[GMP]

The LTR PV cover adds effective volume to the header area of the pipe at lower RPM. This is because when the the PV drum valves are closed to the cylinder exhaust ports, the other side opens the PV chamber to the header area. The Trusty cover includes a replacement left drum valve, that engages a spring that is preloaded by the knob. This has the effect of adjusting the total PV spring force by adding to or subtracting from the force of the governer's spring, depending on the setting, making the valve open sooner or later.

 

[stay_upright]

OK thanks GMP - I am still al little surprised it has a noticeable effect though since I would estimate the area of the LTR PV cover to be 1/100th of the expansion pipe so the change in effective volume should be minimal....

I suspect something else is going on though since the exhaust gas from the cylinder goes directly into the pipe at low RPM but does not go directly into the PV chamber (not without going through 180 degrees anyhow...)

 

[GMP]

Its the ratio of PV cover volume to HEADER volume, not the entire pipe. The change is subtle, and will also depend on what pipe you are running it with.

 

[iancp5]

I would guess it's to do with change in pressure and as the PV chamber is connected right at the beginning where pressure is highest it could have a sizeable effect. There may also be some reflection effect at some point too. It may be small compared to the expansion chamber but it's big compared to the volume of the cylinder head when the exhaust port opens.

 

[socalscott]

OK thanks GMP - I am still al little surprised it has a noticeable effect though since I would estimate the area of the LTR PV cover to be 1/100th of the expansion pipe so the change in effective volume should be minimal....

I suspect something else is going on though since the exhaust gas from the cylinder goes directly into the pipe at low RPM but does not go directly into the PV chamber (not without going through 180 degrees anyhow...)

Consider that FMF sold spacer rings that installed at the pipe header. You can get changes with an 1/8".

The chamber is not a flow thing, just as the intake Boost Bottle isn't. It's strictly volume per the header section of the pipe. BTW, exhaust does go instantly into the chamber. It's not 180*, not even 90*.

I installed a DMC KIPS spacer on my OEM piped '89 KDX200. It was much smaller than LTR's and it changed response to MX. That's significant cuz that motor had zero snap.

 

[stay_upright]

So what is the layout for this thing? i.e. does it go cylinder - exhaust valve (LHS rotating one) - PV/LTR chamber - pipe header?

so the exhaust gases flow out in that order?