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post #21 of (permalink) Old 12-18-1999, 08:44 PM
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Re: 650 cluching & gearing

Whoops, never noticed this post when I posted the last one. This is why I purchased the heavy hitter weights. I am not thrilled at cutting the clutch to fit the heel clickes and the thunder shifts screws are easy to change. Have not noticed belt slip on the 600 yet but have not run it much due to poor snow conditions. The gains where from proper rpm and faster shift. Kept the heavy weights in and changed to a straight angle helix and lost 7 mph in the same distance. I put the other helix back in.

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post #22 of (permalink) Old 12-18-1999, 11:30 PM
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Re: 650 cluching & gearing

I won't even begin to try and match your engineering explaination of what you are trying to accomplish. All I can tell you is what I have found to work for me. I thought that I had the perfect setup with lightning weights and a 50/36 helix. Stock spring up front and a yellow in the secondary. This setup ran great, I was very pleased with the performance over stock.

As a result of trying to get more heat in my SLP single pipe, I added the heel clicker weights. More mass on the weights makes the engine work harder and generates more heat in the pipe. Well in the process, I found that the new setup does generate more heat in the pipe and pipe temperature comes up faster than the old setup. I have noticed an improvement in the responsiveness and track speed with the new weights, and stock helix now too. The heel clicker weights are about the same amount of money that had spent on lightning weights and helix. I can sell both of them for about what I paid for them so I'm not out much. Some times you just have to try things and experience them first hand to determine if you are getting what you want. Things do not always work in real life the way that the paper says they will. There are factors that can not be put on paper like feel and snow conditions.

When you finally get what you want, you should write a book about your findings. I would hate for all of this research to go to waste on one sled.

Mark
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post #23 of (permalink) Old 12-19-1999, 01:51 AM
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Re: 650 cluching & gearing

Mark, can you tell us what spring you used ? How about the weights- how much weight did you put where and what was the total? Thanks

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post #24 of (permalink) Old 12-20-1999, 10:21 AM
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Re: 650 cluching & gearing

You mentioned your sled fell flat on it's face with heavy weights and a stiff secondary spring. Assuming the rpms were where you wanted them, likely the problem is you have so much clamping force on the belt at mid-high speeds that you're throwing away hp.

Everything I've read indicates that this biggest problem at high speeds with these cv transmissions is at higher track speeds there's too much belt clamping. If you can figure out a way to have higher clamping at low speeds and less at high speeds you'd have a better top end and still control slippage at low speeds.

I talked to some guys running the Polaris clutches in their formula 500 cars. They all run low helix angles (typically a constant 34 to 38 (most try to run 34) degrees to reduce the high speed friction loses and maintain reasonable clamping at low speeds. They spend a lot of time trying to optimise the helix angles to find something that reduces the upshift on deceleration or in typical snowmobile lingo provides better backshift (by using steeper angles), and something that minimises the clamping at high speeds (smaller angles). The "art" is to have a steep enough helix to have good throttle response coming out of the turns and a small enough initial angle for a good top end. They tend to run different helix's and springs at different race tracks for this reason.

From a maximum track hp point of view (ignoring driveability) you'd almost want a variable helix that starts small and increases at higher clutch openings. You'd then have to tweak the primary setup considerably to compensate for the high clamping at low speeds and lower clamping at high speeds. In reality this would give poor throttle response, so it's not practical for trail use.


Steve S.
http://home.off-road.com/~ovo/members/sshaw/sshaw.htm
post #25 of (permalink) Old 12-20-1999, 01:15 PM
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Re: 650 cluching & gearing

The engine was down a few hundred rpm on the heavy weight test along with high sec preload on a stiff spring. Like I mentioned this is something that I am going to work on as it was doing what I wanted. Backing off on the sec and grinding the weights will be next. I think this may work out but we will see. Not sure when i can get at it.
The cars can relate some but they have different factors and needs. One of them would be acceleration off the line.
A lower angle provides better backshift and more side force on the sheave compared toa higher one. Think you had it backwards, unless I read it wrong.
Did you get any snow? It was looking pretty good here for a few hours untill the big wind came and stripped it all away. Have some pretty big drifts around anything that trapped the snow. I did get out for a few hours in the blizzard. Talk about hard up for a ride!

post #26 of (permalink) Old 12-21-1999, 02:24 AM
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Re: 650 cluching & gearing

I think we're talking the same thing...

higher angles - less backshift/upshift, rpm's are less affected by torque (throttle), stappier throttle (assuming rpm's are kept up)

lower angles - more backshift/upshift, higher clamping loads (more proportional to torque), rpm's are affected more by torque (throttle position), potential for sluggish throttle (if upshift enough for rpms to drop below torque peak)

I am getting very frustrated with the weather. They were calling for 15 cm (6") today, but instead we got hours and hours of freezing rain and then the temperature went up to 5C (41F) and what snow we had on the ground is gone. Yesterday they were forcasting significant snow this Thursday - now it's flurries...

I've been talking to a budy of mine (the guy with the ZR500) about driving north/west or east between Christmass and New Years to find some snow. 4-5 hours in any of those directions there's a couple of feet. This is supposed to be "Snowy Canada"!!!


Steve S.
http://home.off-road.com/~ovo/members/sshaw/sshaw.htm
post #27 of (permalink) Old 12-21-1999, 08:33 AM
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Re: 650 cluching & gearing

Minus40, I've got another question for you (probably should post in a new message - but knew you'd read this...we're still talking tuning...).

Do you have the timing spec's for the 1990 Indy 650? (they are apparently slightly different for each year they made the 650). I've tried to set mine up for 20 /-0.5 at 7500 rpm and 27 /-2 (or 0.162") at 3000 rpm (from the Polaris dealer).

The problem is 20 at 7500 is advanced by 2.5 on the stator markings and gives me close to 30 at 3000. I've been compromising with just under 19.5 at 7500 and a little over 29 at 3000 rpm.

When I bought the machine it was running stator markings lined up at 17.5 at 7500 and 27 at 3000 rpm. (probably untouched from when Polaris built it)

What did you like to run? I'm thinking of simply aiming for the 20 at 7500 and assume that 30 is ok at 3000 (it only idles there anyway & my plugs are showing quite a rich mixture). Most of my other toys I tend to run about 2 advanced to get a little more out of them, but this is 3 over spec at 3000.

Steve S.
http://home.off-road.com/~ovo/members/sshaw/sshaw.htm
post #28 of (permalink) Old 12-21-1999, 11:15 AM
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Re: 650 cluching & gearing

Steve, you do have some of it backwards. It should be higher angle= less backshift, more upshift and lower angle= more backshift, less upshift. I know this is correct, try it out.
You got me on the timing specs. I can't remember what I did but I do know I had adjusted it. If I can find my papers from then I will get back to you on that.
Well I think we have just enough snow to do some riding now. Supposed to get some more today. Hope you get some soon so you can test all your ideas out! Happy holidays!

post #29 of (permalink) Old 12-21-1999, 12:11 PM
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Re: 650 cluching & gearing

I think we're just talking about slightly different things. I believe you're talking about only changing the helix and seeing the effects.

I'm talking about a complete clutch weight and spring design using a specific helix. What I mean is once the system is tuned to provide the correct engagement rpm and peak hp rpm during wot accelerations you get the effects I described above.

The way the few clutch gurus whos brains I've picked approach clutch tuning is as follows (it also makes sense from an engineering perspective):

- think about the type of throttle response you require, the rpm shift between peak torque and peak hp, and select a helix (in a perfect world you want the upshift at light throttle to keep the engine at or slightly above the peak torque rpm). If maximum speed is important, keep in mind steeper is less efficient at top speeds and make a compromise selection (not as steep).
- figure out how much belt clamping is required for no belt slip (once the primary has fully engaged, but before shifting occurs) and select a secondary spring that works with the helix to provide this minimum at all times (the steeper the helix, the stronger the secondary spring required).
- select a primary spring and weights and keep tweaking the primary until the rpms are where you want them throughout the entire wot throttle range.
- if the throttle response isn't what you wanted (due to clutching) or the belt is stealing too much high speed hp select a different helix and start over.

If you take this approach the big descision in the system design is which helix to run. It drives the selection of everything else and the big tradoff is steeper angles keep the rpms more constant (once everything is optimized) and smaller angles place a more appropriate clamping load on the belt relative to engine torque. If you go with too high an angle and have a peppy machine but the top end will be down somewhat and the belt will wear faster at high speeds.

One of the many antiquated machines I have is a 1966 Olympic (I have a barn full of cars, snowmobiles, trucks, differentials, transmisions, engines, ring & pinions, posi units, etc., etc.). It doesn't have a helix at all (effectively running a 90 helix). That system is unaffected by engine torque, just track speed (once moving). The rpms for a given speed are constant, regardless of how much throttle is applied (well, extremely close). One advantage to this is all 9 hp is available instantly at any time because the engine always operates close to its peak hp.

Apparently the historic reason for the use of a helix was to get around the over clamping of the belt at high track speeds. Prior to the helix, belts were failing regularly on all of the higher performance machines (25 hp and up). The ability for the engine to run a lower rpm under lighter throttles for the same track speed and having a better top speed were secondary advantages. There have also been major improvements in belt designs over the years also.

I'm envious of your snow... They now even took away the falling snow picture for Thursday (indicating we're not getting any) at the weather web page for Ottawa:

http://weather.ec.gc.ca/forecast/yow.html

Hope you have a good holiday and get lots of sledding in. Where abouts are you located?


Steve S.
http://home.off-road.com/~ovo/members/sshaw/sshaw.htm
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