Last edited:
power valves.... block or not?
- Thread starter Clarke673
- Start date
I
IQRIDR
Well-known member
Ok I am going to plug them off this weekend, put in some pink exhaust valve springs from the old 800 VES motors, and I will report back with my exact results. My sled pulls 8250 flat right now, 8300 on the trail so I will add a gram and see what it does. If the wash and plugs look good, and it pulls the same RPM with more weight, I'll definitely be keeping them plugged.
I will report back with concrete results. I will be testing at sea level- 4,000 ft elevation.
I will report back with concrete results. I will be testing at sea level- 4,000 ft elevation.
Duh, Do it!!
G
gman086
Well-known member
It was an HONEST question for an '07 800R, not an E-tech NOR an '08, and I OWN A PRO ALSO (WHICH IS WHY I'M READING) SO STEP OFF! I can see why many stay away from SnoWest because of dealing with those making lame assumptions and lame retorts like yourself! I'll talk to Tom Dines tomorrow about the problem and report back; he knows a helluva lot more about this mod and can respond in a mature manner!
UNBELIEVABLE!
G MAN
Last edited:
Since you are carbureted you likely wouldn't have to do anything as a result of this. Your fuel is regulated by float bowl pressure and vacuum created by flow in the air horn.
Suggesting something that might work for a carbureted sled as a benefit for a fuel injected is just plan inappropriate.
Modern fuel injected 2 stroke run on a map and have very limited ability to adjust to changes made to their air flow system. So as said above when the valve opens at an unpredicted time the map is not making a parallel adjustment to deal with this so there will be two points on the map that will be wrong for this operation. 1 when the valve open-it will be fat, 2 when the valve was suppose to open—it will be lean. This in turn may or may not be an issue depending on how you ride and it likely will not be a problem at full throttle because that is not one of these two points.
G
gman086
Well-known member
Not entirely true starting with the '07 REV which has an ECM that IS tied in with BOTH the DPS (float bowl pressure) and the TPS and that DOES have an affect on what the RAVE solenoids do or are supposed to be doing. Bottom line is I have a lean bog off the line that I didn't have before the block off mod. Who knows, maybe it's just fouled plugs or too large of a plug gap. I'll be speaking with Tom tomorrow and he's one of the first to figure this mod out so... stay tuned.
Have FUN!
G MAN
Last edited:
Does the 07 800r have two sets of exhaust valves per cylinder, one on the main port and one on side ports? Are both sets contolled by the solenoid? If they are and both are opening at the same time I bet that is too big of drop in flow resulting in too large of flucuation in flow crating a lean bog. Maybe we need to move to the Ski-doo forum. I've never owned one but have work on many on the trail so i've learned a few things riding around them over the years. Good luck.
Ok forgot thats not true I own to 1972 elans in perfect condition that are a kick to ride.
Ok forgot thats not true I own to 1972 elans in perfect condition that are a kick to ride.
G
gman086
Well-known member
They're a triple guillotine design with ears for sideports. Tom pins them together so they all open at once. I think you might be right and I need to add fuel. Will discuss in the Doo section but would still like to know if this is an issue for doing the mod to a Pro.
Thanks for your response!
G
C
Clarke673
Somewhere between too dumb to quit and flat earth
soundsgood. to be more specific i was on hard snow with about 8" of fresh. I am about 230 pounds geared up. sled is a 11 assualt 155 and all stock with an HPs can. I was at 6500-8000 feet.
Hey, if you could, report back what Tom says in this 4M, think you're on to it. On my non-ECM mods, rave spring pressure changes had noticeable impacts to midrange RPM, disguised as clutching ghosts. Damn things work. Regarding dumbass comments, at least those of us that know you and all your sleds just chuckle 'bout it. If peeps can't drink and type, you can imagine how the drink and ride thing goes...
G
gman086
Well-known member
Will do. I did hear back from a very reputable forum member who confirms the problem as stated by Cardiac Kid. The fix was to unpin the guillotines and go back to the small internal springs but still keep the valve hoses plugged like suggested for the Pro. Apparently Dave Trygstad is the one who started this whole mod. Would be good to get his input too.
Have FUN!
G MAN
G
gman086
Well-known member
I heard from Tom and he said there shouldn't be that problem because he includes stiffer springs with his RAVE mod which does help prevent them from opening too fast off the line. He feels my problem is more related to using the wrong starting rate spring for his clutch kit and is sending me a couple to try.
So... using a stiffer spring under the cap should work for the Pro too IF there is the lean bog. I think I'd like to go that route for doing the mod on the Pro regardless. The stock spring is orange, whatever that equates to. Maybe someone has a race manual with the different rates and can tell us what the next stiffest one is?
Cheers,
G
So... using a stiffer spring under the cap should work for the Pro too IF there is the lean bog. I think I'd like to go that route for doing the mod on the Pro regardless. The stock spring is orange, whatever that equates to. Maybe someone has a race manual with the different rates and can tell us what the next stiffest one is?
Cheers,
G
Last edited:
FWIW, I did brown 600ho springs (stiffer) on a piped 800ho mod years ago running +8200rpms, and it took away the midrange RPM drop I had, so his advice is consistent with my experience. Thanks for the update! Back to poos...
G
gman086
Well-known member
Well unless you understand what exhaust valves do and what the mod does then you're not going to benefit. IN FACT flatlanders like yourself and NapaMatt are better off NOT doing the mod and even going to a stiffer spring as opening up sooner at sea level has no benefit. You'll just lose some low end torque that can be a big benefit on your trails! Power valves are NOT brand specific, developed by Yamaha in the late 70's! Here is some good info: http://www.alfagroupnews.com/snowmo...ctic-cat-variable-exhaust-valve-system-basics
Have FUN!
G MAN
Last edited:
G
gman086
Well-known member
It wasn't meant as a diss! There are some real performance needs/differences in exhaust valve settings for sea level riders... just ask BJ at Sled Heads Racing in MN about his trail torquer kits!!! I grew up riding in MI and had plenty of fun there too!
Cheers,
G
1/4" fuel line shutoff valve?
Would installing a 1/4" fuel line shut off valve above the "T" coming off the powervalves work? If it would do the same thing as installing a plugged hose on the valves you would have the option of just turning the valve to unblock them again.
Would installing a 1/4" fuel line shut off valve above the "T" coming off the powervalves work? If it would do the same thing as installing a plugged hose on the valves you would have the option of just turning the valve to unblock them again.
Now there is a great "out of the box" idea!
