RPM and Track Speed fall flat in powder! Need Clutching Help Please

[AKpow]

My sled is an 07 M8 all stock except for a STM 11" Secondary with a SnoPro Green Spring and a 52/44 helix @ 0-5,000' elevation. Primary has 75G weights w/ Y/W primary. First day out in really deep snow with this setup and i could not get above 37 mph track speed in a moderate climb and RPMs would hit maybe 7600 then fall off to 7,000. The snow was at least 2' all day and was a lot like oatmeal. Anytime i tried to climb anything the sled would top out then fall on its face. It performed well just boondocking in the trees, but man it would not climb.
Every other ride out this year i have been in decent powder or windblown and the sled would rip and hold RPMs. usually seeing 7600 to 7700 RPMs all day. But not in the deep, pretty much got stomped on the hill by a couple of XPs.


Do i have too much initial angle on the Helix. I have a 48/44 that i need to try and i was going to swap it out in the field yesterday but didnt have all the tools with me. I am just tryin to get an idea as to what changes i need to make for more consistent clutch performance.

thanks

 

[Coxy]

I dont think your going to be able to pull that much helix. Even the 44 seems steep, even for your elevation.

 

[Arctic Thunder]

I dont think your going to be able to pull that much helix. Even the 44 seems steep, even for your elevation.

I agree way to much helix. Get a 40 or even a 38 straight or a 38/42 progressive and see what happens. Also sounds like you might have a bit to much weight.

IMO 37mph track speed sounds about right. Could be a bit higher. But you shouldn't expect anything over 40mph. But you need to hold the R's. A shallower helix will help.

Thunder

 

[Icedog]

I agree that that is ALOT of helix to pull. I'd think a 38* or 36* will work alot better, with closer to 73g weights I would guess.

 

[AKpow]

Thanks for the replies. I will try a lower angled helix this weekend.

One thing i forgot to mention is the STM Secondary is a Torsional clutch that is the reverse cam style like the older Arctic Cat (pre-Diamond Drive) Secondaries if that makes any difference. I assumed they ran a little bit higher helix angles, i have no idea where i got that assumption from. Luckily these older style helixes are cheap at the sled salvage.

I am gettin up 7700 RPM but it wont hold, thats why i was thinkin it was the helix and not the weights. I will swap helixes first then go from there. Thanks for the advice.

 

[Burn Down]

As stated above to much helix come back to a 38* or 40* & drop some primary weight maybe 70ish should get you to 8000.

 

[Coxy]

At that elevation why would he go to 70's? Or 8000rpm for that matter? Unless i missed where he said he had a pipe, 7700 or so is a good ballpark to start at. He could very well turn 75's at the lower elevation, its just trying to shift way way too fast. Not to mention its probably lacking in belt squeeze and making things hot.

 

[bigjb]

I may be all wet but this has been my experience. I would guess it's more the green spring than the cam angle. I have made the mistake of having too much secondary spring to get good backshift and the stiff spring does not allow the secondary to upshift to build speed. The initial rpm spike would probably be from belt slip and then settels into the running rpm where the secondary is not shifting out where it needs to be. I would guess that your primary is considerbly hotter than the secondary when you check it. I think the 48/44 would not make much difference being that you will be in the 44 while climbing anyways. I would try a softer spring to see if you can pull consistant rpms on the flats and then try it on a hill to see if it will bachshift to your liking. But I'm kinda learning at this clutching thing so I could be all wrong too.

 

[Burn Down]

At that elevation why would he go to 70's? Or 8000rpm for that matter? Unless i missed where he said he had a pipe, 7700 or so is a good ballpark to start at. He could very well turn 75's at the lower elevation, its just trying to shift way way too fast. Not to mention its probably lacking in belt squeeze and making things hot.

Your correct I thought he had a slp pipe, anyhoo he still needs to see about 7900 rpm thats peak power stock.

 

[DonoBBD]

If it is an open ended helix drop in goodwin's blue/yellow secondary spring with that helix. IT is still loose but the 11" may comp for it. That spring is ballanced with a 48/42 and shift assist. The spring rate is 295/395 but in a cat clutch more like 195/290. You can crank in the adjuster to make up for the helix angles and you will find the sweet spot.

You are headed in the right direction for the DDrive. I run a 60/90 in my 600 and it rips but the spring is top secret. It will back shift on the track stand with no load on the track. This is the key for powder.

Don.

 

[AKpow]

No pipe or engine mods. all stock

Dono,

Its a torsional spring setup using the older style reverse cam helix, like the used on the king cat, so its not the open ended helix. I can adjust the spring tension by moving the end of the spring into a diferent hole.

Thanks for all the replies.

 

[DonoBBD]

No pipe or engine mods. all stock

Dono,

Its a torsional spring setup using the older style reverse cam helix, like the used on the king cat, so its not the open ended helix. I can adjust the spring tension by moving the end of the spring into a diferent hole.

Thanks for all the replies.

Crank her in till the bog is gone. Trust me on this. Those helix angles are not bad in the old style helix.

Don.

 

[AKpow]

Crank her in till the bog is gone. Trust me on this. Those helix angles are not bad in the old style helix.

Don.

What i gather from this is the steeper the helix angle the higher the spring rate needs to be. Am i on track with this? The steeper the angle the quicker the clutch wants to shift out, but with the higher spring rate it will increase belt squeeze and not allow the clutch to shift out as fast. And the higher spring rate will increase backshift. correct?

so i could go with a lower helix angle and lower rate spring or run the steeper helix angle with a higher rate spring?

I know you know your clutching Dono as i have read may of your posts on here and other forums (Arcticchat or HCS i believe)

 

[bigjb]

Give the clutch theory thread a read over in the performance/modified section, lots of good info there. Its all a balance, once you get close its easier but getting in the ballpark is the hard part. Maybe check to see what some of the guys running the older cats are using for a set up.

 

[AKpow]

ttt

 

[CATSLEDMAN1]

Engine VS Clutch's

One way to approach this kind of issue is step back and ask yourself:

are my clutch's telling my engine what to do.........


or is my engine telling my clutch's what to do ?

Most riders will prefer a clutch setup where your right thumb controlling the engine is dictating to the clutch's.

From your description of different snow conditions and how your sled is reacting it sounds like your clutching is pretty close, problem is once in the heavier deep snow and more drag on the sled you went rite over the divide from being able to control sled performance with your thumb, to the clutch's overpowering your motor. So now you have to go back over to the bright side of sled performance where your engine is running the show.

OPTIONS out on the snow :

make sure your belt deflection is optimal !
more spring pressure on your secondary........so another hole in the OLD HOLE system, or screw in a little more spring pressure on a well outfitted DD, on a stock late model M.......no option here.
check belt and clutch's for cleanliness, carry a 3M scrotch brite and some kind of detergent in a film cannister or similar, take off the belt and shine up your clutch's and rinse with snow, painfull but necessary and often a pretty good improvement.

MONDAY EVENING IN THE SHOP : I think being slighty too light on the weights keeps your motor in more conditions running the show, your weights are toooo heavy. So, grind a couple of grams off the tips and be prepared to do it again. Heavy weights are not a manly thing !! and not a sign of good performance. Your clutch combination is not Arctic Cat, so no reason to think M8 range of stock weights are going to work.

Different secondary clutch with unknown geometry........gotta test for correct helix, who knows, the numbers mean nothing. As secondaries have gotten more efficient helix anges have been coming down and meaning less.
You see sleds today with 80-175hp running the same helix..........tells me that the new cat secondary can find pretty much optimal shift, 15 years ago it took a dozen helix's to tune all the cat models, that's why the old reverse cam is close to being aluminum scrap.

Suspension or clutch's............a stiff spring with little preload will give the widest range of good performance, the green cat spring is pretty good for that. Judge those secondary springs by wire diameter and length, you'r there.

And next week with different snow conditions it will all be different.........so chase it around until you find a good compromise, but keep the motor on top.

 

[1badm1]

You are trying to run to much weight. You only need enough helix to keep the belt from slipping in the secondary. You will be fine with the 52/44 helix as the 11" clutch has a lot more belt to sheave contact area than the stock cat secondary. As you go up in helix angles you need to back off of the weight in the primary, because the secondary shifts easier. I would guess at your elevation you could run a 52/48 with no problem if you go with lighter weights.

 

[AKpow]

ttt