bajardine
New member
I finally got my Viper head mods done on my '03 Mtn Viper. I took a set of SRX 600 heads and opened them up to the 700 bore and then cut them to end up with a squish measurement of .055-.058. I ran it this weekend and it ran great. I previously went from 144" to 151" and dropped the gearing to 21/42 per Tom Hartman's recommendation.
Now that I have the heads done, I need to dial in my clutching. We were pulling some hills in the 7,000+ altitude range and my RPMs were hitting 8500-8600 max. According to the Viper dyno graphs I've seen and the instructions from SLP for my pipes, I want to be in the 8800-8900 RPM range. I need to raise my engine speed by 300 RPMs. I pulled the fly weights out of the clutch tonight and found they were still stock 8EK-00 instead of the 8DN-10s that SLP recommends. I've searched alot on the subject and have seen several members' recommendations. One member recommends "1 gram to each weight = 3 grams=approx 300 rpm's". Another member recommends "1 gram to each weight will drop rpms by approx 100, not 300".
I just finished the chapter in Olav Aaen's clutch tuning handbook. He lists the formula: F=MRV^2 He then gives an example for an engine running 8500 RPM with 50 gram weights. He says to go from 8500 to 9000 RPM you do the following: Force difference = 9^2/8.5^2 = 1.12 or 12% To find the gram weights you need to run, you divide the starting weight of 50 grams by 1.12 and it gives you 44.6 grams.
In my case to go from 8600 RPM swinging 39 gram weights to 8900 RPM I calculate Force difference = 8.9^2/8.6^2 = 1.07 and then 39/1.07 = 36.44 grams. This is close to the second member's comment of 1 gram to each weight drops (raises) RPM by 100. So if I need to go down to 36.44 grams per fly weight, will the 8CH-00 flyweights work for me? They weigh 35.32 grams. I'd be 1.12 grams short. What are my options for making up the difference? Is there much of a difference in the cam angles to be concerned about?
Now that I have the heads done, I need to dial in my clutching. We were pulling some hills in the 7,000+ altitude range and my RPMs were hitting 8500-8600 max. According to the Viper dyno graphs I've seen and the instructions from SLP for my pipes, I want to be in the 8800-8900 RPM range. I need to raise my engine speed by 300 RPMs. I pulled the fly weights out of the clutch tonight and found they were still stock 8EK-00 instead of the 8DN-10s that SLP recommends. I've searched alot on the subject and have seen several members' recommendations. One member recommends "1 gram to each weight = 3 grams=approx 300 rpm's". Another member recommends "1 gram to each weight will drop rpms by approx 100, not 300".
I just finished the chapter in Olav Aaen's clutch tuning handbook. He lists the formula: F=MRV^2 He then gives an example for an engine running 8500 RPM with 50 gram weights. He says to go from 8500 to 9000 RPM you do the following: Force difference = 9^2/8.5^2 = 1.12 or 12% To find the gram weights you need to run, you divide the starting weight of 50 grams by 1.12 and it gives you 44.6 grams.
In my case to go from 8600 RPM swinging 39 gram weights to 8900 RPM I calculate Force difference = 8.9^2/8.6^2 = 1.07 and then 39/1.07 = 36.44 grams. This is close to the second member's comment of 1 gram to each weight drops (raises) RPM by 100. So if I need to go down to 36.44 grams per fly weight, will the 8CH-00 flyweights work for me? They weigh 35.32 grams. I'd be 1.12 grams short. What are my options for making up the difference? Is there much of a difference in the cam angles to be concerned about?
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I run high altitudes and all I usually do is tighten up the spring in the secondary. Raises RPM about 400 rpm amd makes for very quick backshifts. Might not be the recommended way but it works for me.
stingray719 said:
When you say you "tighten" up the spring, are you switching the actual spring to a stiffer spring or just a tighter wrap (60 to 80 or 90)?
Once again this is kinda old school...lol. But I turn it as far as I possibly can by hand and set it there. Been doing it so many years I am afraid I have never looked to see what the actual setting is.
bajardine
New member
Wrong secondary spring?
Okay, so I pulled the secondary off tonight to see what was in there. Lo and behold, not what I expected. SLP recommends the green spring at 5-9,000 ft set at 80 deg wrap. From 9-12,000 ft they recommend the silver spring set at 90 deg wrap. The previous owner had the white spring in there which is two springs stiffer than the silver spring and it was set at 90 deg wrap. Not sure just yet what having too stiff of a spring set at too much wrap will do and if it will affect my engine RPMs. Time to dig out the clutch tuning handbook. Any body know off the top of their head what having the secondary set up like this will do to the RPMs?
Okay, so I pulled the secondary off tonight to see what was in there. Lo and behold, not what I expected. SLP recommends the green spring at 5-9,000 ft set at 80 deg wrap. From 9-12,000 ft they recommend the silver spring set at 90 deg wrap. The previous owner had the white spring in there which is two springs stiffer than the silver spring and it was set at 90 deg wrap. Not sure just yet what having too stiff of a spring set at too much wrap will do and if it will affect my engine RPMs. Time to dig out the clutch tuning handbook. Any body know off the top of their head what having the secondary set up like this will do to the RPMs?
02ViperMtn
Member
subscribed
dirtjumper895
New member
I would assume the primary RPM's would go up, because the engine has to have more RPM's to make enough shift forcein the primaries flyweights to make the belt shift through/into a stiff secondary setup.
Someone correct me if my theory is wrong.
Someone correct me if my theory is wrong.
That's what I would've thought. Don't most loosen/ unwind their secondary by 10 - 20 degrees or more when going off trail/ powder. I could be wrong but that'm my thought. Maybe go from 6-1 (70 degree wind) wind to 3-3 (60 degree) or 3-2 (50 degree), or down a bit like that........dirtjumper895 said:
9801srx
Member
totally opposite of what you said. the more twist the more rpm ,less twist the faster the clutches will shift and the lower your rpm will be. on ice or good hard packed snow you can use less twist. then when you go off trail you can increase the twist to maintain your proper rpm.Super Sled said:
Don't know if this will help you dial in but for a Mountain Viper ported, 20cc domes with stock pipe and can, at 6500' average elevation I'm running 8DN-10 with 2.44 grams each hole, YWY primary spring but a Rapid Reaction secondary, 8500 steady rpm with 185-190# loaded rider, 22/40 gears and 9 tooth drivers. Seems to be a good balance for on trail, in powder and for steep climbs.
My clutching experience is lots of trial and error with detailed notes for each sled. I have found that different sleds react different to the ramp weight, such as a 1 gram change on one engine may change the rpm by 250 where only a 1/2 gram on another engine may do the same. Kind of have to devote a few hours with my little box of rivits, springs and ramps to really getting a sled dialed in.
For riding in loose deeper snow and powder I tend not to get overly high with the secondary angle as the backshift can cause the nose to dive - which can get you into trouble. For aggressive riding on winding trails, the steeper backshift can work for you going into corners but too steep can also get you into trouble on ice or slick snow.
My clutching experience is lots of trial and error with detailed notes for each sled. I have found that different sleds react different to the ramp weight, such as a 1 gram change on one engine may change the rpm by 250 where only a 1/2 gram on another engine may do the same. Kind of have to devote a few hours with my little box of rivits, springs and ramps to really getting a sled dialed in.
For riding in loose deeper snow and powder I tend not to get overly high with the secondary angle as the backshift can cause the nose to dive - which can get you into trouble. For aggressive riding on winding trails, the steeper backshift can work for you going into corners but too steep can also get you into trouble on ice or slick snow.
02ViperMtn
Member
i understand that reducing the twist will genereally decrease rpm slightly. You would think a stiffer spring will increase RPM, however, in this case haveing a much stiffer spring in there may not be allowing the primary to shift all the way up the sheaves, thus resulting in the engine working a lot harder than necesarry and not being able achive peak rpm.
Possibly try the silver at 90 as suggested by SLP and see where it puts you.
Possibly try the silver at 90 as suggested by SLP and see where it puts you.
mod-it
Member
It's odd that you have the EK weights in your Mnt Viper. Was it originally a short track that was long tracked? The 8EK weights were stock on a short track viper, but the Mnt vipers came stock with 8dn-10's.
Tightening up the wrap when riding powder is so it will hold a lower gear instead of shifting out too soon. It's kind of like down shifting a dirt bike when hitting some sticky mud so the engine doesn't bog down. With as stiff of a spring and wrap that you are using, I'd say the engine certainly isn't bogging down. More like it is being held in too low of a gear and has the power to be able to shift into a higher gear and still pull it.
Seems like a pretty stiff spring and amount of wrap. I'm running 5-9000 feet, but I stayed with the green spring and use 70 wrap. My 8dn-10's have 3.6 grams in inner and outer hole. It was fine with just the 3.6 grams in the inner hole and empty outer, like SLP recommended, until I put the flo-rites in. Then I had to add 3.6 grams to outer hole to get rpms back down to 8900. My gearing is still the stock 40-21. With this set up I'm turning 8900 when climbing and maintain 49-51 mph track speed. By the way, what helix are you running? Stock short tracks came with a 47, and stock Mnt vipers came with a 45. I'm running a straight 43 and love it, it was a big improvement over the stock 45 that it came with.
I don't claim to be a clutch guru, but I would try a green or silver spring and start at 70-80 wrap and see where the rpm's are at. From their I'd adjust the rivets in the primary until rpm's were holding at 8900. Keep in mind that you may over turn the rpms at lower elevation, but once you get up higher and get out in the powder they will drop 200 or so. When I start out from the unloading area in the places we ride I'm only at around 3-3500 feet. My rpm's will hit 9100-9200 until we get up on top, but once up into our play areas they hit 9000 when I first turn it on and then drop and hold at 8900 when climbing.
Tightening up the wrap when riding powder is so it will hold a lower gear instead of shifting out too soon. It's kind of like down shifting a dirt bike when hitting some sticky mud so the engine doesn't bog down. With as stiff of a spring and wrap that you are using, I'd say the engine certainly isn't bogging down. More like it is being held in too low of a gear and has the power to be able to shift into a higher gear and still pull it.
Seems like a pretty stiff spring and amount of wrap. I'm running 5-9000 feet, but I stayed with the green spring and use 70 wrap. My 8dn-10's have 3.6 grams in inner and outer hole. It was fine with just the 3.6 grams in the inner hole and empty outer, like SLP recommended, until I put the flo-rites in. Then I had to add 3.6 grams to outer hole to get rpms back down to 8900. My gearing is still the stock 40-21. With this set up I'm turning 8900 when climbing and maintain 49-51 mph track speed. By the way, what helix are you running? Stock short tracks came with a 47, and stock Mnt vipers came with a 45. I'm running a straight 43 and love it, it was a big improvement over the stock 45 that it came with.
I don't claim to be a clutch guru, but I would try a green or silver spring and start at 70-80 wrap and see where the rpm's are at. From their I'd adjust the rivets in the primary until rpm's were holding at 8900. Keep in mind that you may over turn the rpms at lower elevation, but once you get up higher and get out in the powder they will drop 200 or so. When I start out from the unloading area in the places we ride I'm only at around 3-3500 feet. My rpm's will hit 9100-9200 until we get up on top, but once up into our play areas they hit 9000 when I first turn it on and then drop and hold at 8900 when climbing.
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bajardine
New member
Okay, this is what I'm thinking. I'm trying to find a set of used 8DN-10s per SLPs recommendation. Until I can find a set, I'm going to pick up a grn/wht/grn spring with a couple of shims. I'll grab some rivets and or bolts to play with my 8EKs for now. I'm thinking my Viper may have been a short track to begin with given that there's the 8EK weights and a ylw/wht/ylw spring in the primary but I'm a little puzzled because it has 144" rails and what looks to be a stock tunnel extension. I've since added Hartman rail extensions to 151" and 20/42 gearing. I talked to the owner of the local shop and he said I might be able to get away with turning the white spring down to 60* wrap. I think I will try this until I find a used green or silver seconday spring.
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bajardine
New member
Mod-it,
What size track are you running? I'm considering moving back down to a 40T gear on the bottom.
What size track are you running? I'm considering moving back down to a 40T gear on the bottom.
mopar1rules
Active member
I have a green and silver spring for sale. Pm me.
02ViperMtn
Member
definately relax the twist on the secondary some. Maybe try that first. Your cluchtes will be fighting each other with the stiff springs and become inefficient.
mod-it
Member
bajardine said:
I'm still running the stock 144.
A simple way to see if your sled was a short track originally or if it was a Mnt is to measure your ski stance, center to center. A Mnt came with a narrower stance than the short tracks, they had a 38.5" stance to help with side-hilling. Another thing that concerns me now is if you have 8-tooth drivers or 9-tooth. The short tracks came with 9, Mnt with 8. This is important to check, the gear ratio will be different between the two. I can't imagine that they would've stayed with 9-tooth drivers, you should have 8-tooth on it.
As far as gearing I know that A K MntViper is running his 151 Viper with the stock 40-21 gearing and is able to get the same 50mph track speed that I do, so they have plenty when triple piped. Keep in mind that these sleds were geared for 120 hp and the pipes have given a significant gain. I wouldn't worry about the gearing you have too much, it may even help with your track speed.
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bajardine
New member
mod-it said:
The guy at the local sled shop told me the same thing. He was curious too after I told him the clutch had the 8EK weights in it. I went home and measure and I've got the narrower ski stance. Definately an original Mtn Viper. It had 8 tooth drivers on it when I swapped them out for anti ratcheting drivers. I think after I get the clutching dialed in to where I want it, I might play with the gearing a little bit and see if it doesn't affect my track speed and clutch efficiency.
For tomorrow, if I make it up to the hills, I've got a different couple clutching combinations I'm going to try. Since I'm 300 RPM too low, I thought I might try three spring shims first to see if that gets me to where I want to be. I'll run the ylw-wht-ylw spring with three shims and the 8EK weights no rivets. If that doesn't do it, I bought a grn-wht-grn spring to try with or without shims and a handfull of rivets to play with the RPMs. I set the white secondary spring at 60* until my new green spring gets here. I've pretty much decided I want to order a set of 8BU-10's to play with. I was looking at the profiles of some weights with the local dealer and asking him about the 8DN-10's. He said that's what he usually set the Mtn Vipers up with. Then he saw the 8BU's and said that those would be an even better weight to go with over the 8DN-10's. So maybe I will do down that road. Looking for a set now...
mod-it
Member
Sounds like you're on the right path for the clutching.
I wouldn't worry about changing the gearing, should work good for a Mnt set-up.
I wouldn't worry about changing the gearing, should work good for a Mnt set-up.
bajardine
New member
We got back from riding tonight and I'm a little puzzled. We went up probably about 1000 ft higher than our normal play area. We were around 8100 ft. I had the ylw-wht-ylw spring in with three shims and the empty 8EK-00 weights. It was engaging around 4500 RPM which was fine but I didn't see any more than 8500-8600 RPMs. I figured maybe it was due to the additional elevation. No problem. I took out the ylw-wht-ylw spring and put in the grn-wht-grn spring with the three shims. Thought for sure my RPMs would hit higher. Engagement hit closer to 5000 RPMs but when I got on it full throttle, nothing! The stiffer spring/shims combinations did not affect my shift speed at all. I was still only hitting 85-8600 RPMs still. Now I've decided I have to drop some fly weight but with the 8EKs I'm already empty. I have a set of 8CH-10 weights that I think were out of an SXR 700. These are not quite four grams less than the 8EKs I have in there now so I'm hoping these might get me up to where I want to be. I think next weekend I'll put those in without any rivets and see what these do. I'm just not understanding why I'm so far off from what SLPs recommendations are. I'm looking for a set of 8DN-10s but if my sled won't spin the 8EKs up to the RPMs I want, why would the heavier 8DN-10s be any better? Any suggestions? I got my green spring in the mail today so I'll give it a try wrapped at 70-80* next Saturday. I think I'll definately go to the other spot at the 7000 ft elevation mark to be sure the altitude isn't throwing me a curve as well.
I just have to add... 3 feet of fresh powder. It was the best powder riding I've done in three years. Just haven't gotten out enough last two years.
I just have to add... 3 feet of fresh powder. It was the best powder riding I've done in three years. Just haven't gotten out enough last two years.
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