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post #11 of (permalink) Old 12-16-1999, 11:23 AM
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Re: 650 cluching & gearing

Steve, I had a 1.25 133" track on mine. No bog and it was a monster out of the hole. If you figure your clutches are not the bog problem I did change my pilots for throttle response. If I can remember it was rich and I went down one. As far as engagement I cut my weight heels to get what I wanted which was 5000. Top speed was over 100 speedo so I would guess maybe 90 give or take real speed. Your track should be faster top or just try 22-39. Is that a Polaris blue? If so it is about 120/280. The dk blue is 120/300. One other thing you might like to experiment with is the S series weights. They have more mass in the tip which should give more aggressive upshift. S53B = 49g, S53R = 51g, S55R = 53g.

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post #12 of (permalink) Old 12-16-1999, 01:40 PM
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Re: 650 cluching & gearing

Minus40, where do you get your clutching tech info from?

I had thought of leaning out the pilots one jet size also. They're definitly a touch on the rich side. In warmer temperatures the machine runs rich overall with very dark brown/black plugs. When it is around -40 the machine is a little snappier, but it still has the bog. Also at -40 the plugs are a perfect light rust color. I figured for reliability reasons I'd stick with the rich jets and work the clutching instead. My other machine is a 1978 340 RV (free air) and it required rejetting for every 20F change in temperature, just to keep it drivable. My goal with the Indy 650 was to have a fast machine that didn't require any tweaking during the season for temperatures (our sledding temperatures vary from -40C (-40F) to 5C (41F)).

The spring I'm running is the Polaris blue (I guess those guys were full of bs when I called them - your numbers sound more believable considering it has a fairly short free lengh). Assuming it is 120/280 and it now engages at 4300 (to be conservative when the spring was new but broken in) with the 10AL weights and I want 5000. From physics 101 I assume a 160/280 ((5000/4300)^2*120) would give me a 5000 engagement. EPI makes a 165/280 (almond). Unfortunately it would also pull the max rpm's up too high at lower track speeds. Looking at pictures of variable helix's they seem to start with the small angle (for the low gear ratios) and end with the high angle (for high ratios). A variable helix looks like it would compound the problem, lowering the clamping forces (and thus rpms) at high speeds high torque conditions. A stiffer secondary spring installed in say the #1 location seems like it should help to lower the low track speed rpms and keep the high track speed rpms.

I guess the advantage to the variable helix and a stiffer spring combination is at high track speeds the rpms stay high at light throttle, giving better high speed throttle response.

Do you know the clamping and torsional numbers for the Polaris red secondary spring? Why doesn't EPI publish torsional stiffness numbers for their secondary springs?

Probably a simpler way (changing less parts) to get what I want is to find a set of weights with an appropriate shape. I was originally thinking more mass at the tip was what I want, but that will also keep the rpms up at low track speeds. I'm now thinking if I change the weights I want something that generates a profile similar to the 10AL, once the primary clutch has moved say 0.150", but has less weight hanging over the pivot point below that (decreasing the centripital moment & increasing the engagement rpm).

It looks like there are many ways to get what I want. I'll just have to figure out what's available stock and come up with the right solution (hopefully without too much trial and error ($)).

As far as gears 22:39 is a 1.773 reduction; 21:39 is a 1.857 reduction. Currently I'm running 21:35 (1.667). If I switched to 22:39 I'd need a new 66p chain plus both gears. Obviously, durability wise, it's better to run larger gears, but I was thinking of going cheap and trying either a 20:35 (1.750) or 19:35 (1.842) and sticking with the stock 64p chain. (first I have to keep hoping for enough snow to check out where the belt is running at max speed) Is it really worth going for the complete new chain & gears if the stock ones are in decent condition?

Steve S.
http://home.off-hoad.com/~ovo/members/sshaw/sshaw.htm
post #13 of (permalink) Old 12-17-1999, 12:03 AM
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Re: 650 cluching & gearing

Steve, Wow your doing some thinking here!! Not sure I am qualified to explain this but I can tell you what I think I know. You have to remember though that you can have lots of very different clutching setups and basically achieve the same results. Did you say you where getting Aaen's book? That will be good reading I'm told. I will try to follow your post in replying.

The numbers and such come from various aftermarket catalogs and Polaris manuals. Allot of it I can remember as I am always messing with this stuff.
Your missing out on some hp and lots of performance by not jetting. Cheapest way to get 4-5 hp, more if your sled is real bad. If you don't want to jet you might want to look into the tempaflow or variflow. Heard they work. It is tough to clutch a sled that is not running consistent.

If you want more engagement and are happy with your spring and weights just cut the heels of the weights. You may have to reset the belt to sheave clearance though. Another thing to keep in mind is spring rate. To figure this you subtract the pretension from the finish and divide by sheave travel. If I can remember right it is 1.31 but you should check that figure.

Multi or radius helix’s start with the high angle and shift out to the low angle. If you put a high engagement spring in and you have over rev at the start a radius helix will pull the rpm's down. It opens the clutches faster and the acceleration is greater. If you have never felt high engagement, steep helix and traction working together properly, you are in for one hell of a treat!

Red Polaris sec spring compressed at 2.5 =21 lbs and at 1.375 =44 lbs. Torque in inch lbs at 67 degrees of rotation is 38 and 150 is 84. Give or take 1 on the numbers. One way of guessing the numbers for different springs is to measure the wire diameter and length and compare to known ones. Once you get into figuring out aftermarket stuff you will find out some interesting things.

Almost every weight I have seen has the same curvature, or very minor diff, as the stock Polaris 10 series. Is that what you meant by profile? More mass in the tip will want to shift harder and faster. It won't have higher rpm's as it pulling the motor down due to more aggressive shifting and should top out with the same rpm. It may not backshift like you want.

Lets see if I can explain this one correctly- I suggested larger gears, not for durability but for the torque to the track. It changes the leverages on the shafts. You will notice this in the newer Polaris sleds and others.

Warning!! - this stuff will become addicting and will cause you to spend money on parts that will end up in a box! Oh they may work fine but you just have to try something else because you got another idea.

Good part!! - After a few years though you just look in the box for what you need. I just hate it when new stuff comes out! LOL

Have fun becoming a clutch guru. Next winter you can fill me in on the things I don't know.






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post #14 of (permalink) Old 12-17-1999, 05:40 AM
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Re: 650 cluching & gearing

Steve,
Take a look at the heel clicker weights at http://www.supertorquer.com. Randy has been very helpfull with all of my questions on getting these weights setup. These weights should increase track HP by 20% - 25%. Off the line accelleration in unbelievable on my RMK 700.

Randy wrote an excellent article in SnowTech magazine that explaines how your clutch works and the benefits of the new weight design: http://www.snowtechmagazine.com/fplus/heelclicker.html Go check it out, it is well worth the reading.

If you call him let him know that Mark in Idaho told you about the weights.

Mark
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post #15 of (permalink) Old 12-18-1999, 02:43 AM
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Re: 650 cluching & gearing

OK, I think I've got the clutch system figured out. I've read Olav Aaen's Clutch Tuning Handbook cover to cover twice, read the snowtech arcticle a couple of times, spoken to Olav on the phone this afternoon for about an hour, and performed a bunch of calculations & free body diagrams on the clutch setups. (BTW, I'm a mechanical engineer and when I tweak or custom build something I tend to go a little overboard)

It turns out I was wrong with the helix assumption earlier. As minus40 said it starts out at the high angle and transfers to a smaller angle (I was looking at the picture wrong). This would help to compensate for a higher initial load spring - but, there is a drawback to running a variable helix as well as other benifits.

Starting with an ideal, maximum track hp setup:

In the ideal setup the secondary helix and spring should be setup to provide minimum clamping on the belt, but enough so that it doesn't slip. Since the forces on the belt are highest at low track speeds (low gear ratios) and lower at high track speeds, the only way (that I've seen with current designs & read about) to achieve this is through a small helix angle (say 34 degrees) and a soft secondary spring (Polaris red is good for about 80 ft-lbs of engine torque). Any more clamping than required causes extra belt friction and wasts hosepower. The reason this works is the cam provides a clamping force proportional to the torque being applied. Setting up engagement rpms and wot max rpms are then a function of the primary spring, weights, and cam profile (shape of weight contacting roller).

This "ideal" setup does generate a very large amount of upshift & backshift. ie. when you ease off on the throttle the cv transmission will upshift into a higher gear ratio. This forces the machine to feel less peppy when you get back on the throttle because it takes time for the transmission to backshift to the correct max hp gear ratio.

Running a steeper helix produces less variation in rpms (backshift & upshift)with throttle (torque), keeping the engine running closer to the peak hp rpms at all times (for faster, snappier response). A variable helix improves the throttle response at lower speeds, making the machine snappy out of corners, etc. The drawback to both high angle and worse for variable helix angles is the belt clamping forces are higher than required at high track speeds and therefore some hp is wasted in friction (we're only talking a few percent here - but it's still some). The snappier engine response is the reason most people prefer a variable or higher angle helix. The variable helix also allows the transmission to upshift at high cruising speeds better than just a steep helix, so it is a good compromise for performance trail use.

Since changing the helix angle changes the clamping forces on the belt, it requires appropriate clamping forces at the primary to maintain the correct gear ratios. This is done through the primary spring selection and the weights.

There are lots of options to get what I want. One is I could keep the weights the same (10AL), install a higher initial spring load spring (like a 165/280) and install a 42-34 variable helix. This would give me the higher engagement rpm, better low speed acceleration, the same mid-high speed accleration at 8000 max rpm (after some tweaking), and better throttle response on the trails - but I'd loose a tiny bit of top end and it would cost a bunch of $ (Cdn prices: Helix - $100, primary spring - $25, secondary spring - $25 extra springs, etc. to get it tweaked right) in parts (I still might do it).

Another cheaper option is: Since the system works quite well right now everywhere except off the line and does provide close to optimal track hp, I could simply grind the engagement area on the weights flatter or slightly notched to get the engagement rpm where I want it and leave everything else alone. I'll still have the minor delay when cracking the throttle after a curve on the trails, but everything else should work well, including giving me the maximum top speed (provided the shift rpms are set to max hp).

One other option (that may not get what I want) is to go with one of the EPI kits. They have a kit for my machine that sells for $150 Cdn. They won't tell me anything about what is in it, other than they use a variable helix and two non-stock springs. It might be a well optimised kit, with a high engagement rpm, but it might have way more belt clamping force than required and a lower rpm engagement (than I want).

I had a good look at both the supertorquer web page and snowtech's review of the heel clickers and wasn't all that impressed with the technology. Basically what they are doing is producing a weight with a center of gravity that is farther from the pivot point at small primary clutch movements. This will lower the engagment rpms and increase clamping loads (as they say) at low speeds. While everything stated is reasonably accurate, this can all be done with the shape of more traditional weights. One benifit to their system is it is adjustable, but so are Thunder Products kits (the Super Torquer system is $190 US or $285 Cdn and the TPS kit is only $150 Cdn). It's likely that the Super Torquer profiles are not available stock in the standard Comet or Polaris weights, but they could be reproduced.

Anyway this has been quite a learning experience (and I haven't even started tweaking yet). As Olav says, even when you've got the theory and the math for these systems totally figured out, once you start making changes you'll find you still have to tweak to get exactly what you want.

I'll have to see how things go when I start tweaking.

The great news is it looks like we'll be getting the first decent snow Monday night!

Steve S.
http://home.off-road.com/~ovo/members/sshaw/sshaw.htm
post #16 of (permalink) Old 12-18-1999, 12:57 PM
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Re: 650 cluching & gearing

One other thing I thought you might be interested in is related to gearing.

It turns out that by running a lower gear ratio (higher numerically) in the chaincase, althouth low speed performance will be improved (especially off the line), top speed performance is likely to be reduced. This is because the snowmobile transmission is most efficient at around the 1.5:1 ratio. If you run low enough gears that the clutch system is forced to run in overdrive top end will suffer. The numbers work out to about 92% efficiency at 1.5:1, 90% efficiency at 1:1, 83% efficiency at 0.75:1. So if you run gears that make use of 0.75:1 (or near it) you loose track hp.

The complete gearing for a snowmobile transmission (at least current designs) is starting at 3:1 (when slippage stops) up to 0.75:1 in overdrive. Unless you're running deep powder, lots of low speed stuff, towing, or really need the extra peformance at low speeds it turns out it's usually best to run close to stock gears (sometimes higher for drag racing). As long as you have enough engine hp and the clutching is set up right 3:1 off the line should be plenty to light up the track, even with fairly tall chaincase gearing. The key is to run a very tight belt and run high enough engagement rpms to not bog (as well as have a well tuned engine). 3:1 only occurs with around 1" of belt movement (when checking belt tension - Polaris calls for 1.25"). A loose belt quickly changes the starting gear ratio for the worse. To tight a belt will drag at idle.

In my case I'm going to mark the pulleys and check out what ratio the machine maxes out. If it's around 1:1 (I expect it will be) I'm going to leave it stock (can't have my buddy's Cat beating me in top end...). Right now my belt tension (with 1000 miles on the belt) is just over 1.25". I'm going to set up a new belt for 1" first (before I start any tweaking).

BTW, tonight it's going down to -20C (very cold) and now their calling for RAIN on Monday with 2C temperatures... ARGH!

Steve S.
http://home.off-road.com/~ovo/members/sshaw/sshaw.htm
post #17 of (permalink) Old 12-18-1999, 02:17 PM
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Re: 650 cluching & gearing

You may find that most sleds come overgeared for snow. They just will not pull that much gear even out to 1-1 ratio. Lots of people have proven that a gear change will keep the same top end and in some cases improve it. I don't know if that aplies to ideal conditions like ice racers though. Your sled is geared for 104 mph at 8200 rpm (101.4@8000) at a 1-1 clutch ratio according to the polaris chart. Does your sled with you on it have enough power to do this on ice? what about hardpack snow? You did change the track which slowed you down, so I would say a gear change would be in order in your case. The only way IMO is to mark the clutches and test gears like your planning.
One thing that myself and others I talk to are having problems with is belt slip in the drive clutch in the new high torque sleds. I can get rid of the slip but lose performance in other areas. I have not found a total package as of yet but have some stuff I have not tried yet. You mentioned figuring to duplicate the heel clicker performance with traditional weights. What where you thinking about? Profile or placement of mass?
Just a note that a quick test with heavier weights and steeper helix gained 3 mph (radar) in 500 ft yesterday when I was trying some parts out on a 600sp.

post #18 of (permalink) Old 12-18-1999, 03:44 PM
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Re: 650 cluching & gearing

I'm not sure what my current top end is. Since I installed the track I've wanted to do a radar run (I do have a gun I can borrow from work) but haven't had a chance yet. This year I've taken it for a few rips out in the back hay field, but there's only about 1" of snow.

I'd guess it lost about 5-6 mph on top end with the more aggessive track (on hard packed snow), so it's probably down to around 97-98 mph now. I was going to do the calc on jack shaft rpm at 98 mph and assuming your numbers are right I'd be running it at 7732 rpm. Swapping in a 20:35 (instead of 21:35) would give me 8118, which might be a good compromise. I was also thinking I should try setting the clutching for 8000 instead of 8200 since it seems that's the rpm everyone talks about for a stock 650 (My Polaris shop manual actually calls for 7800 rpm). Keeping it a hair high would help with the backshifting though.

BTW, you mentioned a larger lower gear helps more because of the leverage on the shafts. Actually running a smaller top gear puts more tension on the chain for the same reason that a larger lower gear puts more torque on the driveshaft. So what really matters is the gear ratios. The only real advantage to running larger gears is less tension on the chain, and therefore longer lasting chain & gears.

As far as low speed belt slipping problem, more clamping force on the clutch at lower track speeds is required - what's the best way is the challenge. Installing a lower spring load primary spring and a stronger secondary (a longer one for more axial preload with similar torque would be best, Aaen Performance manufactures long springs for this reason like the Aaen-White Polaris (1" taller than stock, 306 in-lbs/rev & 47 lbs/in) will do this, but will definitely have more clamping force than required at high speeds (and increase friction loses).

Running a lower initial helix angle is probably a better compromise, allowing the applied torque at the secondary to clamp the belt tighter. It will pull the rpms up at low speeds though. A softer initial load on the primary spring would fix that, but also lower your engagement rpms.

Have you tried any of the Polaris notched racing weights (01-48.5g, 02-49g, 03-32.5g, 04-57.5g, 07-52g). These are specifically designed to bring the engagement rpms up by about 20%, but still provide high clamping loads after engagement - allowing a lower initial helix angle, a softer primary spring, and less belt slip at low track speeds and still maintain high rpm engagements. Because of the non-linear force during engagement you have to run a small primary belt gap (0.020" or so - as you do) to smooth the engagement. I believe the remainder of the profile is similar to the S series, so a higher spring rate primary spring would be used (like a dark blue). Experimenting would still be required to dial in these options.

Do you work at a Polaris shop and have all sorts of weights, springs, helixes available to experiment with?

Steve S.
http://home.off-road.com/~ovo/members/sshaw/sshaw.htm
post #19 of (permalink) Old 12-18-1999, 06:19 PM
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Re: 650 cluching & gearing

I'm not sure what would be the best way to duplicate the heel clicker weights, but if you wanted to reverse engineer it you could calculate or measure the actual center of gravity for the weight and find a very thick weight with the same profile. Now you'd have to grind the thickness of the heavy weight more at the tip to get down to the same C of G and total weight. It would be tedious and I'm not trying to say easy - it's just there's nothing very special about them.

I'm sure Polaris and Comet have experimented with similar weights that have a center of gravity farther from the tip.

Another, but more involved way would be to calculate the actual forces that would be produced for a given rpm during the full travel of the weight. Once you have this you could design a profile for a constant thickness weight that would produce the same force profile. I'm quite sure it could be done.

Do you figure that improvement on the 600sp was due to reduced slippage of the belt? (I assume the rpms were down with the helix and heavier weights, so I guess it could be you were above the peak hp rpm before and now you're upshifting faster)

Steve S.
http://home.off-road.com/~ovo/members/sshaw/sshaw.htm
post #20 of (permalink) Old 12-18-1999, 08:23 PM
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Re: 650 cluching & gearing

Steve, yes you should try 8000. Much better to under rev your hp peak than to over rev imo. Peak torque is often 200 rpm less than peak hp. Sleds seem to fall flat pretty quick over revving. Certainly don't assume your tach is correct though it's probably not unless you had it calibrated. My belt slip is in the drive clutch. A partial fix that I have been using is belt clearance. It is about .080 right now. Helps out quite a bit and the engine can handle it fine with no bog. I like these torquey engines! I have used notched weights but now cut the heel instead for a couple of reasons. I just recently tried extra heavy weights and heavy wire secondary spring. This worked very well for the slip but the sled fell on its face mid range to top. I never had time to work with it much but is something I am going to play with again. I picked up some TSP heavy hitters also that I am wanting to test also. Sled runs pretty good with current setup but I like doing this and I know it has more in it. Biggest problem is traction, it is difficult to balance everything for snow. Seems to be much easier on ice or grass where more consistent traction can be had.
I have lots of springs, weights , gears etc collected over the years so when I want to try something I just go to my collection. If not then I buy it, within reason of course.
It's snowing here today so I think a ride is in order tonight.

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