Need secondary clutching advice on helix/spring

[beacon2]

Hi all,

I have a somewhat unique question that I'd like your input and advice on, since I know virtually nothing about snowmobiles. So I'll try to pick YOUR brains about what helix and spring to use.

As the posting says, I’m looking for some advice on secondary clutching.

What I have is a little racecar that I run in what's called autocross. They take an open area like part of an airport and set up orange traffic cones and make a small road course. The total length of the entire course is usually about 1/2 to 3/4 of a mile total (sometimes a little longer), with usually about 12 to 14 turns, so you can see it's fairly tight.

The speeds aren't all that fast (maybe 65 - 70 mph tops) because you're really always turning one way or the other. It's more about driver control than speed. Probably the longest stretch of straight-away is 100 feet or so to 'open her up'.

Here's some YouTube videos that might give you a little better idea of what a course looks like. This particular course is longer than normal since it uses more of the taxi-way. They put the slalom in to slow you down some so you don't get going toooooo fast.

The first video is from the inside of another car, obviously not mine. It should give you a good general overview of the type of racing I do.
The other 3 videos are of me but not nearly as good as the other one.

http://www.youtube.com/watch?v=gl32n7LH0pw&feature=related

http://www.youtube.com/watch?v=FR0uxmk2VOQ

http://www.youtube.com/watch?v=k4PxI-QPNWc&NR=1

http://www.youtube.com/watch?v=us4XedRLi5s&feature=related


Those may give you guys a little better idea of what I need to do.

So I guess I need the driven (secondary) clutch to upshift fast and backshift fast so I can 'goose it' coming out of a corner but yet backshift quickly as I'm going into a corner to help slow it down and also be ready when I 'goose it' coming out of the corner. Does that make sense?

There's no snow or hills to contend with as a snowmobile would have, just flat concrete or asphalt with lots of turning. I’m in western Indiana, the elevation is about 600-700 ft. I haven’t weighed the car, it’s probably something around 750-800 lbs. with driver. They start in late spring and going into the fall, so temperatures vary from maybe 55 degrees to 90 or above on the tarmac.

The motor is a Rotax 493 l/c from a 2000 Skidoo MXZ 500. The class that I run is extremely restrictive, only the 493 or the 494 (non-rave version) are legal in the class. All motors have to be bone-stock, no modifications. I've heard that horsepower on these is around 90-95, is that right?

I'm running the stock Skidoo primary clutch that came with the 493 motor. I think it has some sort of a clutch kit in it but I haven't had it apart. The guy I bought it from used said it had a kit but he didn't know or remember what it was. It was on the used motor and seems to work pretty well, although the engagement RPM is higher than I probably need. I’d like to have it lower. I have another primary spring but haven’t put it in yet.

RPM range, I'm not sure. There's no tach on it... yet. I hope to get one hooked up but I'm not sure I'd have time to take my eyes off the course to look at the tach... it gets pretty "busy" out there watching where I'm supposed to be going.

The jackshaft is keyed and is 1" diameter. It currently has an old Arctic Cat button style secondary that I plan to replace with a newer style Arctic Cat roller off of Ebay fairly cheap... unless one of you guys wants to sell me one of yours cheap.

Any suggestions on what helix and/or spring to use? Straight helix, progressive helix? If so, what degrees, what secondary spring, etc.?

I'd appreciate any ideas/suggestions/input you guys might have.

Thanks!

 

[spring snow hero]

I would gear it to go 10mph faster then you think you will go.....but you need a tach to know how fast that will be. then I would try a 51* or 53* straight helix with a sno pro green spring in the secondary....start tight and unwrap till it drops rpm......if it never does, add more helix.

you might ask in the skidoo section for advice on the motor. getting it to rpms and keeping it there is important.....but you gotta know where that is first.

sounds fun!

 

[beacon2]

Thanks for the input. Yep, it's a ton of fun!

Any more thoughts and ideas from anyone?

 

[beacon2]

Any more opinions or has Spring Snow Hero got it right on the money with the 51* or 53* straight helix with the green spring?

Thanks!

 

[Killerk]

I would get a tack hooked up, and do some testing... Other than on race day.
Then post back with what RPM's it is running, what engagement RPM is, and also find out what weights, primary spring, secondary spring and helix are currently in it.
Also give us your impressions of where it seems to work good, and where you think it could use improvement.
You should only need the tack for testing purposes, once dialed in you should not have to make extreme changes... Maybe run the driven spring with less or more preload depending on the layout of the track.
In a race, obviously you will not be looking at the tack much.
My .02

 

[Killerk]

A speedometer would be helpful also.

 

[winter brew]

You need to do some experimenting, this is alot different than a sled, but I would think with the cat secondary you would end up closer to a straight 44 and a red/white spring. This will be MUCH snappier and more responsive, plus ALOT better backshift. Try a TEAM secondary if you can, or a Polaris button clutch, they all offer different characteristics and one may work much better than the others in your application.

 

[spring snow hero]

I aimed him steep because he is running short bursts and light on power.......plus there should not be much load vary like we see..but...I missed the 800lbs part.....as said it is all gonna be an experiment.....sounds fun. cat helix's are cheap too!

 

[beacon2]

Thanks for the comments, guys.

The guy I bought the car from used to run asphalt ovals with it. I've been running what he had in it, which is a 55*/53* helix. I can't tell what color the spring is, it looks rust to me cuz it's obviously been in there for awhile.

On the asphalt ovals he was racing, he'd have time to "wind 'er up" whereas I'm running short bursts, like Spring Snow Hero said. Then on the brakes hard to get into the corner, then on the gas hard again.

I was looking in my box of spares that came with the car and I found a 53*/44 helix. Again, the secondary I have now is the old button Arctic Cat. Will these helixes that I have work ok on a newer Cat roller secondary when I get one?

I'm a little confused. Spring Snow Hero says he "missed the 800 lb. part" which is why he aimed me steep. Does that mean that Winter Brew may be closer on his recommendation on the straight 44* with the red/white spring?

I know it's going to take some experimentation but I'd like to get as close as possible. I hate to buy 3 or 4 helixes and 3 or 4 springs, put them in and test for 2 minutes and discover they aren't going to do what I'd like... then toss them in a box and never use them again.

Yep, it's gonna be A LOT different than a sled. Keep the comments and suggestions coming, I appreciate them all as I try to sort out what's going to work best for me for what I'm doing.

Thank you all again!

 

[spring snow hero]

how does it pull the helix you have in it? are your tracks always flat? if they are those two I told you might actually be pretty close....but I would guess on the steep side. I would surely run a straight helix. snowmoblies are lighter, but have more rolling resistance then a car...so I would guess they sould be pretty close in comparison, since a sled full of fuel and a rider that is not anorexic (sp) would be about 750 lbs. a sled will make a bit more power due to the cooler air and running temps....but we fight the altitude. realize that any helix choice is going to be very dependant on the gearing as the helix is load detecting in nature.

have you had a chance to open the car up and see how fast it goes? if it is geared to go way faster then you will ever go, a shallow helix is going to help a bunch....not as much as gearing more for you speed, but it will help. if you are geared correctly, you want to run as much helix as you can pull without pulling the engine down on accelleration. I would run a spring like the red/white in a roller and possibly a green wound light in a button clutch. the spring being stiffer will help you on the in and out of the throttle, and when you make hard turns.

if the car pulls the 55/53 well try the 53 straight, if it seems to be a dog out of the hole.....gear down or step twards a 47 ish helix.

I would think on a flat track with the 80ish hp you have somewhere in the low 50's high 40's would be the ticket.....all depending on gearing. the stiffer springs are a must for racing.

 

[spring snow hero]

also, the cat helix's are only about 10bux a try, used.... and pretty easy to get rid of.

 

[snoman159]

I've got some used cat springs and helixes for the older roller clutch if you are interested. Most of the springs only have a few runs on them so they are almost like new. The helixes are about the same. Not sure exactly what I have but PM me if you are interested and I could check into it. I also have a Polaris button secondary with a couple of springs and R8 & R11 helix for sale if you wanted to try that route. I think I also have a set of the super slippery buttons which would probably help for your racing application. I think SSH is on the right track with high 40s for a helix angle. You may want to try taking a permanent marker and making a line on the primary clutch to see how high your belt is travelling in the clutch. This will give you a good idea on how close your gearing is without buying a speedo. You should still invest in a tach to help with the tuning process though.

 

[Snowflapper]

Go and do some testing on your own and find out what works. Read the Cat clutch tuning guide and that will give you a idea of how things work!!!!

 

[beacon2]

Hey, guys, GREAT advice! I appreciate it all. Yeah, I'm still a little confused since I don't know squat about sleds and clutching, but it's starting to come together in my brain.

Actually, the car does pretty good the way it is. I simply want to go to a roller secondary to decrease some resistance instead of the old button clutch that's probably been on there for years and years.

Out of the hole, the car has plenty of punch. Really too much. If you nail it hard, the whole car shakes violently trying to get a bite because of wheel hop. I have to "feather" it taking off for about 10 feet or so, then nail it. Part (or all) of that is because of the axle flexing, I think I may put another bearing in the middle of the axle to help eliminate that. Then I'll probably smoke the tires.

Just for your information, I did some checking on sprockets. The front is a 13 tooth, the rear is 72 teeth. I have a 15 tooth front, I may try that since I'm going to be running slightly shorter tires this year. I don't have any more room on the back to go with a larger gear because of clearance issues.

Why should I be looking at a straight helix? As I said, the 55/53 in it now doesn't seem bad... but I have no reference on how it "should" feel. I also have a 51/44 in the spare parts box. I don't know what the benefits are of the various one. And if I just move what I have over to a roller clutch when I get it, is it going to change the characteristics much?

Again, thank you, guys!!! Keep the comments coming, if you want. I can use all the help I can get.

 

[spring snow hero]

try the 15 tooth and more spring tension.