Oh a update. I am sorry. That is impressive. Only negative I have found with 8dn is my primary is starting to groove right in middle of sheaves at cruising shift position. Its real common and started to be noticeable at 9000mi. Next season will be looking for new Primary clutch hopefully a mint used one from Barn Of Parts or others.
Sno-Xr
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Ok guys, hoping no one minds revisiting this thread, hoping to get a tried and trued update to the 8dn debate. After reading this thread, I still have a few questions Im hoping can get answered.
If the 8dn is wider, shouldnt the primary be shimmed to accept it? What prevents belt grab at idle?
Did I also read that it(8dn) has a different angle profile than the stock Viper belt? If not, what does Ulmers clutch machining accomplish? Or do the clutches have the same angle as all the older Yami clutches that run the 8dn?
Is shimming the secondary for belt height all thats necessary?
As for the primary wear, I had to replace my Nytro primary around 9000 miles also....heard this was a common issue
If the 8dn is wider, shouldnt the primary be shimmed to accept it? What prevents belt grab at idle?
Did I also read that it(8dn) has a different angle profile than the stock Viper belt? If not, what does Ulmers clutch machining accomplish? Or do the clutches have the same angle as all the older Yami clutches that run the 8dn?
Is shimming the secondary for belt height all thats necessary?
As for the primary wear, I had to replace my Nytro primary around 9000 miles also....heard this was a common issue
Shimming is all thats needed. Angle is the same. The 8dn is longer so the shimming actually tightens the 8dn.
hognit09
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Is there any performance benefits to the 8dn besides longer lasting and cheaper ?
TPAY243
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This is from my personal findings I have seen no performance gains with 8DN belt, but I have seen a loss with my 190 hurricane tuned viper. I have tried many different belts and have gone back to 8JP. Everyone says the 8DN is a harder compound then the 8JP but I think the total opposite I think the 8JP is the harder of the two. The gates belt is too soft and grippy when warm for my liking. All I can say is try it and see what happens it's very easy to do, if no performance loss then 8DN is a little cheaper.
ClutchMaster
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They are both pretty hard belts. The difference is the 8jp will disintegrate easier preventing wear on your clutches. Both are fairly stiff making them suck horsepower at higher speeds. The 8DN is about 7/16” longer and the same width as the 8JP. So little bit less top speed with the 8DN but not really noticeable.
I ran the 8DN for awhile and it lasted, with nice trail manners but I don’t like how it wears the clutches so I went back to the XS825.
Sno-Xr
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Thanks for all the replies! Recently picked up a 15 s-tx dx, and am installing the Thunder Products Venom clutch kit. Trying to decide if I should go ahead and switch to the 8dn.....which will be VERY convenient considering my kid will be my Nytro riding partner....or should I stick with the 8jp??
What is the XS825? Gates?? Any shimming involved? Benefits??
Thanks again
What is the XS825? Gates?? Any shimming involved? Benefits??
Thanks again
Aftermarket 8JP equivalent. I run a 8DN primarily but for a little less rpm and top speed I put my XTX 5033 on which is a Dayco 8DN equivalent. I would run it all the time but expensive! My advise. Pick a belt and stick with it. In my testing every different belt brand does effect rpm a bit. If your picky it will require clutch tuning when switching if you have a rpm goal in mind. For those of us used to tuning the clutches its not a big deal but if switching belts and expecting same rpm its not going to happen.
sxr70001
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What Cannondale said! I ran the 8DN for awhile because the original 8JP was so dirty, but have switched back to the Ultimax 8JP equivalent because I felt like I was leaving a few mph on the table. It lowered my RPM by around 300 and I have been adjusting clutching to get it back. As far as a spare I still carry an 8DN because everybody I ride with uses it and it would still get me home if I needed to use it.
Studroes144
TY 4 Stroke God
Keep in mind the width of different belts. 8dn and 8jp are same width. I’ve had great luck with gates carbon belt in the 8jp length which is a bit wider than the Yamaha belts. Not sure how other aftermarket belts compare. My biggest reasons for always going back to the gates belt is because of it being wider and still the shorter length it makes the sled very responsive since belt deflection is tight unlike the 8dn. With 8dn you can shim the secondary so the ride height is proper..but deflection is still going to be off unless you get the secondary machined. You can throw an 8dn on and it’ll work, but it’s going to bring factors into the equation that’ll make it a bit more of a challenge to get the clutching working properly if you’re fussy about the details. Always remember..the 8jp vs 8dn thing came about because of people having issues with the 8jp belt itself, not the length.
Sno-Xr
VIP Member
Cost, less belt dust, and the fact my other sleds run the 8dn make it more appealing, but would prefer the performance not suffer if it can be helped. What rpm is ideal for the Viper?
Also, noticed others complaining about the belt not reaching the top of the primary, but havent seen the conclusion to as why. Any thoughts? Mine doesnt appear as if has been either, but the owner before me did mostly boondock riding.
Also, noticed others complaining about the belt not reaching the top of the primary, but havent seen the conclusion to as why. Any thoughts? Mine doesnt appear as if has been either, but the owner before me did mostly boondock riding.
Studroes144
TY 4 Stroke God
Yamaha clutches are designed so the belt will not reach the top. Machining can be done to the primary to achieve this..but also will need to do the secondary as well because if your primary shifts further than what your secondary does you’ll have bad problems. Also, when considering getting clutches machines for overdrive, think about what your top speed is. With the exception of the mountain sleds and maybe one or two early year LE sleds the viper is geared for 105 mph in stock form +/- 1mph. If you’re not reaching those speeds then the only affect that machining your clutches for overdrive will have is that you’ll have less money in your pocket and a machine that doesn’t go any faster.
Sno-Xr
VIP Member
Thanks, good food for thought. I definitely need to put in some seat time for a base line before getting too deep into mods 
I just installed the Big Venom clutching, but think I need to re-place the secondary rear bushing....it felt really sloppy when I had it disassembled. Any preference on new bushings? OEM or is there a good aftermarket bushing? I havent checked Thunder Products, but will tonight.
I just installed the Big Venom clutching, but think I need to re-place the secondary rear bushing....it felt really sloppy when I had it disassembled. Any preference on new bushings? OEM or is there a good aftermarket bushing? I havent checked Thunder Products, but will tonight.
I will add that even with gearing dont expect any big gains unless big power is applied. The stock gearing is pretty much matched right on for the power we have. Now dont get me wrong. If you are the type who is always trying for the most on every long straight there will be issues with stock belt,gearing and clutching. I dont think they ever thought we would hold it tight for minutes at a time trying to eek out every mph! I dont forget the fact that if my stock setup with 8jp was held tight for minutes it would only last 3-500mi or less before absolutely coating the secondary with rubber. I went through 4 belts first season. None blew just totally lost all performance and trashed clutches every time right between 3-500mi. I did what was working for everyone else and switched to 8dn and never looked back. It was way more consistent. Obviously if Winders can run that 8jp belt I should have been able to but it was ride time and took the simple way out. I have a clutch setup now that any change I make is immediately rewarded with a change in rpm and its repeatable. So I can go up or down in rpm at top end and see if any gains are made almost as accurately as a dyno. Shoot for 8900-9000rpm that keeps you off the limiter and allows for those rare perfect conditions. Then decide is 100-105 enough to see under perfect conditions. Be realistic. Just cause a Nytro feels faster and shows faster on speedo doesnt mean it is faster. Race them. It will come down to who gets the jump mod for mod. This sled handles so well at speed it just feels slow. Honestly. If you feel like more is needed can join me in the quest for 110mph NA or be a cheater and throw a Turbo on it and sky is the limit then.
Sno-Xr
VIP Member
Ive owned my share of sleds and top speed has never been a major goal of mine, but would like to dial it in so that it is performing the best it can considering what it is. I dont plan to try and keep up with the Apex's and Winders past the 300' mark.......unless the trail is whooped to beat hell, then they'll be trying to catch me!! 
Thanks for all the input
Thanks for all the input
