Found our missing power.

[stingray719]

Its lost in the clutch, the primary actually. After the 8DN debacle I went to work studying why this sled was so different from the Nytro clutches. I noticed our Viper came with a 2 stroke profile in the weight. That being a bump in the heel to raise take off revs (as 2 stroke have high horsepower not torque) and then a level ramp for about a third of the profile then a steeper ramp to raise rpm. And yes, why? This is a torque motor not a 2 stroke. I put the flat profile Nytro weights in (Matt from MPI suggested this, and this is what I did to our other boosted Yamahas so it wasn't anything new) and cut to desired rpm and that helped but it still seemed like something was missing. I mean this sled is a lot lighter than a Nytro and should be faster. So I came up with a bizarre test that worked.

All tests with flat profile 8FS weights cut down to 50 grams for above 10k altitude running. Weather about 25 degrees 3 inches snow on top of crust at 10k altitude. Race against 2008 Nytro with Can and a few add ons and a 2012 Nytro with 190hp Turbo


1. Stock clutches - Primary spring 35 open, 101 Shift -----------------------------------------------------Viper slightly slower than Nytro, Turbo blows it away

2. Stiffest primary spring made for this clutch (that I could find) Primary 45 open, 135 shift------------Even up with Nytro, turbo blows it away

3. Spring of my own design (exact details later)-------------------------------------------------------Viper blows away Nytro, and runs about one length slower than Turbo from stop to 50mph



Further testing and sharing of info with vendors before final details are released, can't have our two favorite Technical Wizards In Training telling me once again I don't know what I am talking about

 

[loudelectronics]

what do you mean by 45 open and 135 shift? Are you talking about spring rates? If so is this pounds, KG, NM and also at what compression as in 1" 2" or full?

 

[stingray719]

what do you mean by 45 open and 135 shift? Are you talking about spring rates? If so is this pounds, KG, NM and also at what compression as in 1" 2" or full?

Yamaha green-white-green

 

[Nytros rule]

Nytro XTX versus Viper XTX both have the same weights (8GL) Nytro came weighted .9, 4.5, 4.5 Viper came weighted 3. 3.6, 3.6. Same primary spring (blue silver blue). Nytro was white/white secondary versus Viper Pink secondary.
Blue Silver Blue is 35 KG. preload 2 KG. Rate

 

[stingray719]

Nytro XTX versus Viper XTX both have the same weights (8GL) Nytro came weighted .9, 4.5, 4.5 Viper came weighted 3. 3.6, 3.6. Same primary spring (blue silver blue). Nytro was white/white secondary versus Viper Pink secondary.
Blue Silver Blue is 35 KG. preload 2 KG. Rate

Nice information but what bearing does this have on the 8FS weights and stronger primary spring as I used?

 

[Nytros rule]

If I used that flat weight and strong spring I wouldn't be able to move, I would not be able get off the rev limiter.

 

[Nytros rule]

Nytro XTX versus Viper XTX both have the same weights (8GL) Nytro came weighted .9, 4.5, 4.5 Viper came weighted 3. 3.6, 3.6. Same primary spring (blue silver blue). Nytro was white/white secondary versus Viper Pink secondary.
Blue Silver Blue is 35 KG. preload 2 KG. Rate

Nice information but what bearing does this have on the 8FS weights and stronger primary spring as I used?

You need to understand the mountains in Saskatchewan are at least as big as the ones in North Dakota.

 

[FAMILYMAN]

Ya, clutching for sure. Good information.

 

[loudelectronics]

what do you mean by 45 open and 135 shift? Are you talking about spring rates? If so is this pounds, KG, NM and also at what compression as in 1" 2" or full?

Yamaha green-white-green

I am running the green white green spring and white spring on secondary. Has made a huge improvement. I have to add a bit more weight though to my 8Bu as it hit limiter on launch and then settles at 9060 rpm. I would like to try a lower engagement spring though as i think it will helpon take off in the trees.

 

[Studroes144]

I guess that's kinda the beauty of buying a complete clutch kit..in most cases atleast, you're not just buying the product, you are buying all the testing and leg work that has already been done. Lots of guys have had clutch issues right from the beginning of the season, I for one was not one of them but I still seen good gains with my clutch kit and I have continual adjustability for whatever I'm trying to achieve.

 

[stingray719]

what do you mean by 45 open and 135 shift? Are you talking about spring rates? If so is this pounds, KG, NM and also at what compression as in 1" 2" or full?

Yamaha green-white-green

I am running the green white green spring and white spring on secondary. Has made a huge improvement. I have to add a bit more weight though to my 8Bu as it hit limiter on launch and then settles at 9060 rpm. I would like to try a lower engagement spring though as i think it will helpon take off in the trees.

8FS with flat profile gets rid of higher rpm on launch. It will also drop engagement speed with same spring, dropped my engagement around 800 rpm.

Check the chart below and that initial hump in the charts kinda shows how much extra rpm needed to get over weight "hump" in the ramp. Non mountain weights tend to make your engine rev higher on take off and of course that is not needed or wanted on a mountain sled (or one with a torque engine like a Viper) Ergo the 8FS for mountain sleds (widely used in boosted sleds and torque engines)

http://www.totallyamaha.com/snowmobiles ... arts1A.htm

My opinion of course.

 

[Studroes144]

I agree you can work off the torque of this engine and not specific peak hp like a 2 stroke but in the countless hours of clutch testing that we've done, the best performance comes when the engine is able to rev right up quickly and get to peak hp, you want it to get to peak hp quick but you don't want it to over shoot and rev too high, that will more the less ruin the performance of the sled, get it to rev up to 87-8800 as quick as you can and then it should build a little bit from there. My viper runs best on long runs when I'm at 8850-8900 rpm. Any less than that and it doesn't want to pull the sled much past 90 mph. I totally agree clutching is 99% of people's low top end problems. If your rpm is good, check for full shift of the clutches. That will tell u right away what needs to be done, I've heard of people having issues with primary and some having issues with secondary

 

[Buster696]

IMO… gearing needs adjustment on this sled so the radio is below 2.00. If stock gearing for LTX is really 24/50 @ 2.08 ratio then my sled needs to get closer to a mid 1.9 ratio and then we should see more MPH. A 2.08 gear ratio is close to an ice drag 660ft and grass drag gear ratio with a stock track from my old notes that I looked up.

--Buster696--

 

[Studroes144]

IMO… gearing needs adjustment on this sled so the radio is below 2.00. If stock gearing for LTX is really 24/50 @ 2.08 ratio then my sled needs to get closer to a mid 1.9 ratio and then we should see more MPH. A 2.08 gear ratio is close to an ice drag 660ft and grass drag gear ratio with a stock track from my old notes that I looked up.

--Buster696--

Changing the gearing may help but it's not the some issue as some people are seeing good top speeds with box stock sleds and others are seeing very poor speeds..all of which have the same gearing.

 

[scott32]

Congrats on your clutch kit. I think we need an SR Mountain section as to not confuse set up for riding areas