What do power valves do? ME and a few buddies in my riding group were trying to figure it out but no one could really figure it out. Also how would a power vavle delete kit work and how would it effect performance? Thanks!
Stupid question but...
- Thread starter Braaap12
- Start date
I'm not an expert on this, so if I'm wrong somone correct me... but ...
What the variable exhaust valves do is regulate a certain amount of back pressure on your exhaust manifold at varying RPM's .... what this does is help to develop a flatter power band for the motor and make it more driveable. It's similar to VTEC on a Honda car motor, at least in principle.
The only time you would want to "remove" your exhaust valves would be on a sled you were running at WOT only, ie, a drag sled .... the exhaust valves are automaticaly open on any sled that has them at WOT or perhaps even near WOT, depending on the model.
Here, I found ya an article describing them a little better.
http://ezinearticles.com/?Snowmobil...riable--Exhaust-Valve-System-Basics&id=902728
What the variable exhaust valves do is regulate a certain amount of back pressure on your exhaust manifold at varying RPM's .... what this does is help to develop a flatter power band for the motor and make it more driveable. It's similar to VTEC on a Honda car motor, at least in principle.
The only time you would want to "remove" your exhaust valves would be on a sled you were running at WOT only, ie, a drag sled .... the exhaust valves are automaticaly open on any sled that has them at WOT or perhaps even near WOT, depending on the model.
Here, I found ya an article describing them a little better.
http://ezinearticles.com/?Snowmobil...riable--Exhaust-Valve-System-Basics&id=902728
A
aksnopro
Well-known member
hm
i may be wrong but my perception on these things is at whatever designated RPM they move outa the way to allow for more exhaust to exit. and if there not running properly the machine will feel like it falls on its face after 6k rpm, they are key to opening up the power band at higher RPM's. not sure the exact technical details but they get outa the way at the exhaust ports at the designated RPM.
-Aksnopro
i may be wrong but my perception on these things is at whatever designated RPM they move outa the way to allow for more exhaust to exit. and if there not running properly the machine will feel like it falls on its face after 6k rpm, they are key to opening up the power band at higher RPM's. not sure the exact technical details but they get outa the way at the exhaust ports at the designated RPM.
-Aksnopro
2 strokes are very dependent on the exhaust to scavenge and produce power. That is why there is a big bulge in the pipe as opposed to 4 strokes with a straight header pipe. Back in the day before power valves, the exhaust was designed for power in one certain RPM range. Then it was determined that you could alter the exhaust shape and scavenging effect by moving a "power valve" in the exhaust. So in a way, it is like a variable size exhaust. By doing so the "power band" or effective RPM range of a motor is increased making more power throughout a greater RPM range. That's the basic jist of it in a nutshell.
Kind of like having a larger selection of rubber bands in a Volkswagon.
Kind of like having a larger selection of rubber bands in a Volkswagon.
Small exhaust port equal great bottom end power.
Large exhaust port equal great top end power.
Variable power valves give you both, the power valve servo motor pulls the power valves out of the exhaust ports at roughly 7,000-7,500 RPM (I can't remember the exact RPM 7,250?) and give your sled much more power on the top end than it would have with small exhaust ports.
That's why adjusting your cable length is so important. If they aren't adjusted properly, you won't get full power out of the motor because one both fo the exhaust valves will be blocking the exhaust ports.
Large exhaust port equal great top end power.
Variable power valves give you both, the power valve servo motor pulls the power valves out of the exhaust ports at roughly 7,000-7,500 RPM (I can't remember the exact RPM 7,250?) and give your sled much more power on the top end than it would have with small exhaust ports.
That's why adjusting your cable length is so important. If they aren't adjusted properly, you won't get full power out of the motor because one both fo the exhaust valves will be blocking the exhaust ports.
so why would someone 'DELETE' the power valves? what are the pros and cons of deleting them? can someone explain ?
They actually effectively "raise" the exhast port, as well as enlarging it, which raises peak power RPM. You can see power valve engines in the dynosheets, the power has a double hump, one peak for valves closed, the other for open. Gives a much flatter power/torque curve, much easier to drive with varying engine speeds. They add complexity and weight, though, and don't increase peak power at all, so if you are only after ultimate HP, they are just in the way.
John
John
Cool thanks for the replies
Braap,
from what we've seen the delete works best on bigger motors. It works well on the 1200, somewhat well on the 1000, and so-so on the M8. I can speak to the M1000, they gave a very small hesitation/decrease at low rpm, but were a definite gain in the middle, for the weight loss & the mid gain I felt they were worth it.
On the M8 I don't think they would be. For performance & weight loss the supreme tool valves are the holy grail imo, but pricey in comparison to the deletes.
oh btw, they make the sled louder on the bottom & mid for sure... you'd like that
from what we've seen the delete works best on bigger motors. It works well on the 1200, somewhat well on the 1000, and so-so on the M8. I can speak to the M1000, they gave a very small hesitation/decrease at low rpm, but were a definite gain in the middle, for the weight loss & the mid gain I felt they were worth it.
On the M8 I don't think they would be. For performance & weight loss the supreme tool valves are the holy grail imo, but pricey in comparison to the deletes.
oh btw, they make the sled louder on the bottom & mid for sure... you'd like that
haha touche, I wasn't thinking about doing the Delete kit I was just curious what it did. thanks!
