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Discussion Starter · #1 ·
Hello everyone. I’ve just finished rebuilding the engine in my 670. I ported the crankcase and put in the thick base gasket. I plan on putting in a 501 RV and doing the y-pipe mod. I’m trying to figure out what primary spring I should go with. Right now I have the stock one in place and actually don’t know what it is. I’m looking for another 300ish rpm and a slightly higher engagement wouldn’t be a bad idea. I also think I should change the ramps as well. I run a 121x1.5 track right now. Opinions? Thanks a bunch.

I’m not feeling a whole bunch difference in the engine right now. Time to bring the package together.
 

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Google 1998 ski doo racing manual. It gives you all kinds of info on pn and measurements on springs. So you can identify your old spring. Its going to be trial and error.... do you have solid pins or hollow pins? A place to start is to get a adjustable pin weights 16g to 23g. Get a primary spring 200/320 or 230/320 or a 200/350. Some where in those paremeters. Whatever you can find. Might have to buy a few different ones. Either use 286 ramps or 280 again whatever is avail... the 280 alone will bump engagement without changing any of your springs. But your springs are probably tired. Service secondary... rpelace spring and replace buttons. If you go with a 350 finnish youll be adding pin weight to maintain your 8000 rpm at wot. 320 finnish might be bang on at 16 grams. But again all depends how healthy motor is.
 

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Discussion Starter · #4 ·
Thank you kindly for your response/help, I appreciate the input from someone who is definitely more experienced than myself. Right now all clutching is factory and still set at factory specs. I have played with the clickers, but haven’t had any luck. The rpm simply doesn’t change. However, from my research, I probably didn’t wind her out with enough speed to really tell. The clicker adjustment will affect the back half of your speed run.

I believe I have the 286 ramps in her right now. I was thinking about the 280’s, but again research tells me they aren’t wonderful for stubble jumping across these prairies. They are more for drag racing.

I went down to our local Ski Doo dealership looking for TRA clutch parts and options, and the partsman looked at me like I was from Mars. I have a speed manual from 97 and even gave him some part numbers. I wasn’t surprised when they were discontinued. I left with nothing. If I can find parts like you recommended, I will definitely buy all 3 springs. I also want a new pin set.

Any idea where I can find TRA clutch parts? I would certainly appreciate it.

Thanks a bunch.
 

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Take a look at ibackshift.com for a really good technical breakdown of how the TRA and its components work together.

First, figure out what you have for a spring in the clutch currently. Your used spring is probably sacked anyhow, affecting top RPM.
Ensure everything is CLEAN and that the sliding sheave bushing is in good shape. Address this if the bushing looks worn out, or you'll just chase your tail.
Make sure you have a good belt also; something that you can source a new one if needed. (I personally like the 127 PN Doo belt for F/S/ZX sleds)

You want to increase the starting pressure of the primary spring to increase the engagement RPM.
The finish pressure affects top RPM, but so does pin weight, horsepower, gearing, etc.
Personally I'd start with the 286 ramps and get some adjustable pin weights in there.
Figure out where it runs at, and go from there with making a single change and testing.
And keep notes of what you have tried, the conditions, and the results. Too easy to forget; and nice to have something to look back at.

If you're finding springs discontinued, try goodwin, hot rod sled shop, SLP, Wahl Bros
 

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Bombardier Pink / White spring part # 414991400. Will work well with 286 ramps. Start with clicker on 4.
Lynn
PS What year sled do you have?
 

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It’s a 1997
I have one in my garage which belongs to my son. He bought it brand new and it has had a bit of tinkering done to it.
The P/W will wake yours up. Honestly I've forgotten what ramps his has but I'll ask him. He does his own clutches.
Lynn
 

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Discussion Starter · #12 ·
A couple days ago I put in my “cut” 501 RV and did some testing. I wasn’t expecting much and I was correct 😂😂. I certainly don’t have a good enough calibrated butt dyno, as I couldn’t feel anything. Probably worth one or maybe 2hp in all reality. I also did do something that wasn’t recommended, as I simply couldn’t help myself. I ended up removing the centre air baffle and opening up the entry horn in the air box. I was rewarded with more rpm in the end. The tack registers just over 8k now. I couldn’t believe how much difference it made. I was very careful, started out fat and slowly dialed it in. We went to the drag races with it today and my son did very well with it. We were very pleased with the results and how it compared. After all it was the oldest sled in both classes by a long shot.

Next up……y-pipe mod. The additional rpm could benefit from the shorter pipe. Then I tinker with the clutch.

Thanks for all the help so far everyone.
 

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What classes were you running in?
 

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Discussion Starter · #14 ·
We were running in the 700 stock and 800 stock. He placed 3rd on the A side in 700 and 3rd on B side 800. The 2 F7’s he lost to definitely had the launch, the better suspension shows up. What I was really impressed with was how well he was reeling them both in on the big end. As soon as he could hook, he started closing the gap. If he had another 50 feet of real estate(1/8 mile track), he would’ve won first. He definitely had the best mph.

I’m glad we went today as I can see how a higher clutch engagement wouldn’t really help much. I stood close and could see him leave, I could hear the engine hit max rpm almost instantly.

in the 800 class, they had a lot more track. Definitely tougher. We didn’t come in dead last by no means. Still pleased.
 

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Here is what is in the primary clutch now.
Spring Pink / White
Ramps 287
Clickers 3
Pins Stock solid
Secondary is a BRP Roller clutch with a spring pressure set at 18 1/2 #
Running a 1 1/4" track Camoplast Ripsaw (A huge improvement over the stock track) No studs
This sled has never been raced competitively, just a few go 'rounds with other sleds and for a 670 it holds it's own and then some He's embarrassed some newer sled owners.
Most of the miles have been put on trail riding. The roller clutch does give a bit better backshift but is no real advantage under hard acceleration.
 

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Discussion Starter · #17 ·
Guys, I did the y-pipe mod today. Had some issues getting things to line up again. Removing a chunk of the pipe throws the alignment geometry off. It took a little TLC and adjusting, but I got her aligned not too bad.

I took it for a test run and I have it tacking at around 8100ish. It’s definitely over 8k but hard to tell when your trying to drive😂. I think the whole package is coming together. I’m not sure if I should dive into the clutch or not. I have noticed a slight dip in bottom end torque now. It’s not terrible, but I think I can feel it.
 

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Came out of the gate hard and pulled hard all the way.
 
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