Big bore ski-doo

[lancelarue]

A little info for the folks interested.(Mountain sleds only, race sleds different of course)
Series 3 860 TRA / drive
After many years experimenting with countless clutching combinations / primary and driven.
1) I only run at low elevation here in Alaska, sea level to 6,500'. Bear that in mind-(this is Alaska!!)
2) There is no way you can load to potential an 860 up here on the bottom - mid range with any, I repeat, any factory ramps, arms, /oversize rollers etc.
They need to be loaded really hard to work. (a good one that is !!)
So, here's what I've ended up with--
Start with 417 ramps. They will need to be ground from engagement to about 1/2 shift point. Compare them with a 415 ramp. When you're done, you will be lowerthan the 415's all the way to 1/2 point with-out the hump.
Stock rollers= no bushing issues.
I should clarify this is with nothing shorter than a 151" up to whatever.
If you're running stock arms, this equates to more shift on the bottom, able to swing more weight on top for the bigger track.(belt squeeze)
If you're running Thunder arms, it works really well as you don't have to load the bottom of the arms (first hole) to the point the arms are rattling bouncing off the ramps @ idle.
If you have the correct helix / spring in your chosen driven,( one that will hang on to the belt with YOUR load), you'll be happy, I know I am-------

 

[winter brew]

Yep, the BB's do like to be loaded.....have to be to show the gains from what I found also.
I found a ramp similar to what you describe, then also loaded a bit more with spring and initial helix angle. Was able to avoid using HUGE pin weight which seems to wear rollers and arm pivots quicker.
Good stuff-

 

[swrev]

A little info for the folks interested.(Mountain sleds only, race sleds different of course)

Start with 417 ramps. They will need to be ground from engagement to about 1/2 shift point. Compare them with a 415 ramp. When you're done, you will be lowerthan the 415's all the way to 1/2 point with-out the hump.
Stock rollers= no bushing issues.
QUOTE]

Trying to understand the whole clutching thing w/ the ramps so I am just asking a questions--wouldn't grinding the ramps to that point lessen the load on the motor? The ramp would be steeper all the way through and the engine would gain rpm easier. I thought a flatter initial ramp loaded the motor more--clutch shifted easier making the engine torque do the work. Am I backwards in this? I have a turbo XP and am running 441 ramps (my sled did not have the clutch setup that came from the turbo builder), I was going to try and grind them down similiar to what you are talking about to make the engine rev easier. I like the 441 for finish, but it, in at least what I thought was the way to go w/ the ramps, would be the worst ramp for a turbo application--extremely flat initial portion of the ramp??? Maybe all I need is to get a different spring w/ a higher starting point.

Running an 860 also w/ 417 ramps, w/ fully loaded pins and it works great, but slow speed backshift isn't quite what I would like. Did your grind help there?

 

[lancelarue]

A little info for the folks interested.(Mountain sleds only, race sleds different of course)

Start with 417 ramps. They will need to be ground from engagement to about 1/2 shift point. Compare them with a 415 ramp. When you're done, you will be lowerthan the 415's all the way to 1/2 point with-out the hump.
Stock rollers= no bushing issues.
QUOTE]

Trying to understand the whole clutching thing w/ the ramps so I am just asking a questions--wouldn't grinding the ramps to that point lessen the load on the motor? The ramp would be steeper all the way through and the engine would gain rpm easier. I thought a flatter initial ramp loaded the motor more--clutch shifted easier making the engine torque do the work. Am I backwards in this? No you're correct. I have a turbo XP and am running 441 ramps (my sled did not have the clutch setup that came from the turbo builder), I was going to try and grind them down similiar to what you are talking about to make the engine rev easier. I like the 441 for finish, but it, in at least what I thought was the way to go w/ the ramps, would be the worst ramp for a turbo application--extremely flat initial portion of the ramp??? Maybe all I need is to get a different spring w/ a higher starting point. You can run a higher start on your primary spring to slow the upshift with better backshift, but, your engagement is going to go higher. First off, are you running stock arms or Thunder arms or ?
At any rate, if your engine is too slow on the bottom, lousy backshift,you need a steeper ramp = slower shift / more rpm and still keep your same engagement+-.

Running an 860 also w/ 417 ramps, w/ fully loaded pins and it works great, but slow speed backshift isn't quite what I would like. Did your grind help there?

Flatter ramp after grind = shifts out faster = lower rpm more load. Utilizes additional torque of the engine if you have it.

 

[lancelarue]

Driven clutch

Mountain sleds w/ big tracks
Tuning the clutches with all the different options and variables can be confusing / frustrating some times. Lots of aftermarket kits and parts to choose from. All great stuff. It's nice to have options.
Sometimes trying to find the "magic", we lose sight of the real picture.
There is only one torque sensing part of the equation and that's the driven.
If the driven has the wrong helix it will not respond to the torque load correctly. The spring is basically only for minor tuning upshift backshift/ rider preference etc. It will in degrees allow to slow or speed up the shift and if the correct helix is not available will definitely have an effect, but, better to find the correct helix and just fine tune with the spring. Way less bs and variables.
So, the driven senses the load and either upshifts because the torque from the engine is stronger, or backshifts if the load is greater than the available torque from the engine.
If the driven can't hang on to the belt, everything goes south. Typically the drive clutch heat will be hotter as the belt starts slipping, and belt sucks in the driven and the drive loses tension and ability to grab the belt.
If the driven has the correct helix for the load, than the drive needs to be set up to match the driven.You can run huge spring end loads to be able to run big pin weights in the drive and chase it all over the place, BUT, IF THE DRIVE DOESN'T BALANCE WITH THE DRIVEN all you'll end up with is belt slip = heat = bad stuff!!!!!
So, obviously the drive controls the rpm, but it's HOW you get there is what counts.
Example 1
44* helix in a given driven clutch
Engine needs to be @ 8,200 rpm. Hypothetically, you can get there with say a 200# finish on the primary spring with 12 grms weight or say 19.5 grms with a 350# finish on the primary spring. You could conceivably get the same rpm +-. The difference is the SHIFT FORCE. Same target rpm. You say what's the difference? It's SHIFT FORCE. More weight = more force.
So, when you set your drive clutch up, the drive force has to match the set up in the driven!!!!!!!!!
Ramp profiles / roller sizes / spring rates are all tuning tools, but the WEIGHT is calling the shots!!!!

 

[swrev]

Thanks, good information. I am going to start grinding. I am pulling a lot of weight w/ the wrong type of ramps for the turbo for sure after reading this. Turbo kills the torque level at lower rpm but really screams after a little boost. My 48 degree helix probably isn't helping--not builders recommendation either. Going to put in a 43/47 to help from overreving at full speed.

What did you use for grinding the ramps?

 

[lancelarue]

I wouldn't start grinding until you've explored all the options/oem ramps. The only reason I will do it is if ramps aren't available to match the shift curve the motor wants.
Having said that, I know there are a ton of different ramps with the same approx. finish as a 415 with higher engagement and or steeper angles @ the bottom where your turbo isn't spooled up yet. I've yet to get to play with a turbo set up on a sled, other stuff lot's!!!
Rather than going up on the helix angle and loosing belt squeeze(43X47),try a straight helix to simplify things and pick it according to your track size / load / conditions. A turbo would absolutely rip with the helix you're talking about IF you can get up on the snow and plane out, but, if you can't stay on top, and you're in and out of the throttle with some trenching etc. it's going to probably be slipping if you're anywhere close to that 47* range. Drag racing- wfo straight line pulls, probably rip if you had ramps to match-
If you're running a QRS driven, it's going to be hard to beat a Shockwave adjustable helix. Tune for the conditions all the time! Heavy and deep, screw that sucker in to grab the belt, starts packing and setting up, screw it out, match with the clickers to a point. I know some of the guys say they've been breaking some parts on those, but we have good luck here. (in the mountains)
What are you running? Complete set up--------
I'm sorry, got carried away with myself and forgot your question ie. grinding. I built a jig so that the heal of all the weights rests on a common machined surface with a machined pin / nut tightened down on the ramps so everything is straight with the world. Set it up in my milling machine with a good stone with good coolant, keep the stone perfectly dressed so as to stay straight and rest the jig on the table and grind by hand. It's not too bad once you get the hang. Finding long enough good stones poses a bit of problem sometimes.

 

[swrev]

I am unsure of the springs in my setup--didn't write down what they were and tinker w/ enough sleds that I shouldn't guess. My enagement is about 3800 rpm so heavier initial spring is where I'll start. Then put 417 ramps since I have some to 'borrow' and test a different start rate. You are correct on the straight 48 for straight line pulling, it builds speed in a hurry, and actually isn't bad for boondocking. I've never weighed the weights. Stock arms and instead of a pin w/ weights to be screwed in, I've got basically a solid bolt w/ head and all. Appears that it would be about twice(??) the weight I have in the 860. Never have any black marks w/ belt slippage. 860 has a Shockwave and it has held up well for two seasons, I was leary of putting one in the turbo but may have to try it anyway.

 

[lancelarue]

Give me a shipping address here or pm me. I have some ramps I'll send you to try but I need some info.
Spring colors/ #'s you've tried or have now.
Your gearing
Drivers if not stock
Track
Skid
Stock arms? ( or Thunder, Tom's etc.)
I'm assuming stock spring in the driven?
After you try the 441's with the 43X47, your opinion--What don't you like?
Mark the drive clutch inner sheeve with a felt marker BEFORE you make a pull in your conditions and measure down from top of sheeve to rub mark to show me your set up.
If it's still too lazy with the low 43 start on this helix, get a picture in your mind of where the engine comes to life in regards to track speed, shift point on the ramps.
Ex. Feels doggy / lazy, slow backshift until 5 mph, 10 mph, whatever---->
And lastly, most important, what state of tune is your engine? Is it dialed as far as fueling, turbo wheels / housings, size, etc. etc?????? There's also no sense in chasing the clutching if the engine fat on the bottom/ mid or whatever.

 

[swrev]

Give me a shipping address here or pm me. I have some ramps I'll send you to try but I need some info.
Spring colors/ #'s you've tried or have now.
Your gearing
Drivers if not stock
Track
Skid
Stock arms? ( or Thunder, Tom's etc.)
I'm assuming stock spring in the driven?
After you try the 441's with the 43X47, your opinion--What don't you like?
Mark the drive clutch inner sheeve with a felt marker BEFORE you make a pull in your conditions and measure down from top of sheeve to rub mark to show me your set up.
If it's still too lazy with the low 43 start on this helix, get a picture in your mind of where the engine comes to life in regards to track speed, shift point on the ramps.
Ex. Feels doggy / lazy, slow backshift until 5 mph, 10 mph, whatever---->
And lastly, most important, what state of tune is your engine? Is it dialed as far as fueling, turbo wheels / housings, size, etc. etc?????? There's also no sense in chasing the clutching if the engine fat on the bottom/ mid or whatever.

You want to know more about getting this sled setup than I do!

I don't get a ton of riding/testing time but I'll be glad to let you know how it works w/ each change. Have a few changes I am making to the sled/turbo setup before I get too far into clutching. Before any clutching, I am changing to fuel pressure reference off the center section of the pipe, otherwise it was hard to get the fuel pressure to come up fast enough when running above 10lbs of boost, lower boost was not an issue. I am also currently running block off plates instead of powervalves. Valves are going back in w/ a pressure relief valve to see if I gain any more bottom that way, if nothing else, fuel mileage. I burned 16 gallons in one day last year. Both of those changes are going in at the same time. I'll ride it that way for a trip and than start making clutching changes.

Also I apolagize to other readers of this post, I've sort of monopolized it w/ more turbo clutch questions rather than 860.

 

[Ove]

Mountain sleds w/ big tracks
Tuning the clutches with all the different options and variables can be confusing / frustrating some times. Lots of aftermarket kits and parts to choose from. All great stuff. It's nice to have options.
Sometimes trying to find the "magic", we lose sight of the real picture.
There is only one torque sensing part of the equation and that's the driven.
If the driven has the wrong helix it will not respond to the torque load correctly. The spring is basically only for minor tuning upshift backshift/ rider preference etc. It will in degrees allow to slow or speed up the shift and if the correct helix is not available will definitely have an effect, but, better to find the correct helix and just fine tune with the spring. Way less bs and variables.
So, the driven senses the load and either upshifts because the torque from the engine is stronger, or backshifts if the load is greater than the available torque from the engine.
If the driven can't hang on to the belt, everything goes south. Typically the drive clutch heat will be hotter as the belt starts slipping, and belt sucks in the driven and the drive loses tension and ability to grab the belt.
If the driven has the correct helix for the load, than the drive needs to be set up to match the driven.You can run huge spring end loads to be able to run big pin weights in the drive and chase it all over the place, BUT, IF THE DRIVE DOESN'T BALANCE WITH THE DRIVEN all you'll end up with is belt slip = heat = bad stuff!!!!!
So, obviously the drive controls the rpm, but it's HOW you get there is what counts.
Example 1
44* helix in a given driven clutch
Engine needs to be @ 8,200 rpm. Hypothetically, you can get there with say a 200# finish on the primary spring with 12 grms weight or say 19.5 grms with a 350# finish on the primary spring. You could conceivably get the same rpm +-. The difference is the SHIFT FORCE. Same target rpm. You say what's the difference? It's SHIFT FORCE. More weight = more force.
So, when you set your drive clutch up, the drive force has to match the set up in the driven!!!!!!!!!
Ramp profiles / roller sizes / spring rates are all tuning tools, but the WEIGHT is calling the shots!!!!

AGREE!

Moore shift force allso make it moore stable from one day to the next, Supremetool arms is nice and has good bushings in them.

 

[lancelarue]

Big bore Ski-doo / Paragon

Well I'm finally getting closer to break in on a new build. Still have to get the fueling done but waiting until it's completely done breaking in. Motor seems to have a lot of potential, responding well to intake & combustion chamber changes this year.
Thought I would share what's working with the Paragon:
Thunder arms 72.7 total arm weight w/ stock rollers
ground 417 ramps
100X260 spring
58X55 helix with green cat spring 1/4" to 1/2" twist
Good to 5,500'
This is close to what I ended up with last year except for the spring. I had to drop finish to calm the rpm down. I'm thinking this might do it or a 230# finish, we'll see. Clutches balance out really close, cool running.
I'm thinking I'll have to gear up a couple on the bottom to stay out of overdrive.
Snowing, waiting for a riding day!!!!!!!!!!!!!!