Gas powervalves vs servo valves

[Waternut]

I understand the concept of power valves and what they're for but I don't really understand the difference in how they're operated. On a 66e it looks like the pv's are operated by an electric servo motor. Then everyone speaks highly of the gas operated power valves.

What are the differences, benefits, drawbacks, etc.?

 

[SXR-FOREVER]

I'm wondering the same thing..

 

[WFO Speedracer]

Gas operated valves are operated off exhaust gas pressure,the pressure overcomes the spring on the diaghpram and pushes the valve open,its really that simple.On a 66e the valves are opened via a servo motor and two cables,way more complexity than is needed IMHO.The servo motors break ,the cables bind up and break,you have lots more moving parts on the Yami setup.

 

[Waternut]

So basically when the rpms go up the force of the exhaust is too great for the spring and the power valve is pushed out of the way?

I keep reading it's better but seems like it might not open at the best possible time. I can only imagine it's more reliable but is it better performance wise? If all it is, is a regular power valve that isn't powered but has a spring and fancy adjustment knob, why are they so expensive?

 

[WFO Speedracer]

So basically when the rpms go up the force of the exhaust is too great for the spring and the power valve is pushed out of the way?

I keep reading it's better but seems like it might not open at the best possible time. I can only imagine it's more reliable but is it better performance wise? If all it is, is a regular power valve that isn't powered but has a spring and fancy adjustment knob, why are they so expensive?

They are expensive because they are custom made ,one off fabricated components ,unless we are talking about Seadoo RAVE valves,and they are not expensive and come stock on Rotax 787's.:cool2:

 

[SXR-FOREVER]

So other than the risk or the servo valve going to hell there isn't any difference between the who?

 

[WFO Speedracer]

So other than the risk or the servo valve going to hell there isn't any difference between the who?

If you are asking do they both open and close then the answer is yes,its kinda like the difference between a pushrod V-twin and a OHV V twin,do both types of valvetrains open and close the valves yes,are they the same no. :burnout:

 

[SXR-FOREVER]

as in performance..

 

[WFO Speedracer]

as in performance..

Performance no question about it ,Gas valves all the way.The whole Yamaha setup is ludicurous,it takes hours to disassemble clean and reassemble the Yami setup and eventually it has to be done,gas valves take minutes to remove ,clean and reinstall,gas valves react instantly to pressure changes in the exhaust,the Yami setup is electricall operated by a remote servo with cables at that.If you want the truth of the matter the reason the Yami setup uses all that crap is because Yamaha loves to make electronics and overcomplex designs and they couldn't copy the Rotax setup because of patent laws.

 

[Mile9c1]

I would say a servo type setup could perform better if set up correctly, since it is more controllable. They can be set to any position, at any RPM.

Also, gas valves don't react instantly, there is lag in the system even w/o cables. Pressure has to build before the valve will open. And if they are sticky they may not open together or open when you think they open.

The gas valves are of course hands down more simple and easier to maintain.

 

[superramjet]

When kawasaki's factory team was alive, their mod motors had electric servo driven power valves. Gas valves would have been easier but why did they choose not to?. I would think that electric valves can be programmed to open at specific rpms each and every time, a millisecond ahead of the time a gas valve would open after building pressure. I doubt they were trying to create more work, but can easily see how extra parts and electronics would be hard to justify in production craft. Could it be that the electric pvs can perform better but gas pv are simplier and cheaper?. I doubt the patent theory, polaris was running gas valves too on snowmobile motors

 

[Waternut]

I would say a servo type setup could perform better if set up correctly, since it is more controllable. They can be set to any position, at any RPM.

Also, gas valves don't react instantly, there is lag in the system even w/o cables. Pressure has to build before the valve will open.

That was my original thought. Since everyone changes them out on a Yamaha setup, can they not be adjusted to do exactly what you want or is it just too difficult to do?

 

[yamanube]

Performance no question about it ,Gas valves all the way.The whole Yamaha setup is ludicurous,it takes hours to disassemble clean and reassemble the Yami setup and eventually it has to be done,gas valves take minutes to remove ,clean and reinstall,gas valves react instantly to pressure changes in the exhaust,the Yami setup is electricall operated by a remote servo with cables at that.If you want the truth of the matter the reason the Yami setup uses all that crap is because Yamaha loves to make electronics and overcomplex designs and they couldn't copy the Rotax setup because of patent laws.

LOL I like how you totally skirted the question with a paragraph of gibberish.

 

[redrrocket]

snip , polaris was running gas valves too on snowmobile motors

Yes but the polaris operated differently, The pressure, "hole" was located farther up in the exhaust port and it was not as quick as the ski-doo setup.

THey had to change the locations due to patent laws.

They were somewhat easy to tune tho. with a simple change of spring.

Yamaha's servos were programmable and operated automatically to help in cleaning.

The first batch of polaris powervalve cylliders required lots of maintenance

They gummed up with carbon. They had to try and find a cleaner burning oil at the time. 1996-98.

 

[kevbo]

Aftermarket cyl mfgs use gas operated valves for economic purposes. It is not the fastest nor most accurate method of actuation but is the cheapest. Jetskiers dont care about details like that.

 

[WFO Speedracer]

The factory teams didn't really to worry about production costs,during the jet ski racing heydayat the factories would build whatever they wanted regardless of cost.Yes they do have to change designs to get around patent laws,even something as mundane as a seat latch will differ in design and operation,don't believe it just look at the seat latches on each of the sit down watercraft,very few are even close in design.I have seen some of the high dollar stuff that Kawasaki put out,their powervalves were electrically operated and the ignition modules that ran them were state of the art in design.Yes theoritically if you can match the ignition curve to the opening of the power valves you will have a more powerful and responsive engine but the complexity level goes way up as does the cost.There you go Nube a couple more paragraphs of gibberish just for you.

 

[Carbon Blaster]

Yamaha released powervalves in the early 80's & were controlled by a counterweight that was mechanically connected to the crankshaft. A pair of cables were attached to a rotating powervalve in the alloy exhaust port area - the higher the rpm, the more the powervalve would open.
They then moved to an electronic servo which was controlled by the cdi & changed the rotating powervalve to a flat sliding type.
This type is still used today in their motocross & grandprix bikes.
The difference in the powervalve requirements between bikes & jetskis are:
Bikes have constant hook up to the track surface
Bikes take a longer time to rev out & utylise a gearbox to help
Bikes are not constantly covered in salt water
Jetskis are not mechanically hooked to a track surface
Jetskis power is on/off & free rev to full rpm quicker
Jetskis speed catches up to rpm, not the other way around
An electronic powervalve would not see it's full potential with a jetski as the rpm is so on/off
Electronic powervalves would require so much extra mantainance compared to a pressure type powervalve to keep salt water out, & how many people in the scheme of things do heaps of mantainance on their skis
A pressure type powervalve is best suited to a jetski because it matches the throttle response of the motor, on/off
A proper electronic powervalve setup is very expensive to build as you need a servo plus a new cdi that has the powervalve mapping built in, or an aftermarket ignition that has the capability of switching a circuit on/off where selected, but this system would still only be an on/off system, not a progressive one like proper factory electronic powervalve systems are

 

[rkm]

You get better acceleration if the valve opens fully at WOT, even from a stand still. Thats something you cant replicate with gas operated valves.

 

[Waternut]

You get better acceleration if the valve opens fully at WOT, even from a stand still. Thats something you cant replicate with gas operated valves.

Uhhh I'm just a noob in power valves but doesn't that completely defeat the entire purpose of power valves? I mean if off idle the valve raised completely, it'd be no different than running without pv's. I could be wrong but just seems logical...

 

[#ZERO]

You get better acceleration if the valve opens fully at WOT, even from a stand still. Thats something you cant replicate with gas operated valves.

I guess you never had the power valve stick open because the most common symptom is lack of bottom end acceleration.

The electric servo motor control power valves have a greater degree of accuracy as well as being able to vary the opening of the valve and be tuned to conditions. Yamaha engineers realized that by altering the height of the exhaust port they could effectively change the engine power delivery thereby having optimal power and torque across the entire rev range.