Ski Doo 850 Turbo clutch changes 20.5 v 21 (and misc tuning)

[Dynamo^Joe]

Chris) Joe was just wondering if you could start up a thread sharing the clutch changes for the 2021 turbo sleds and how it will effect performance VS clutch kits over the 2020 models. As well it seems there is an array of new clutch arms, what does all that mean for users and clutch kit builders.

Joe) ok lets look at 20.5 vs 21 specs first.

2020.5 x 850T
Ramp-984, Pivot 38mm @ 16.7g, Cam 40 deg. Clutch Spring 150-350. Black Spring 160/303

Settings
Clicker 1; 0~8000f (165hp)
Clicker 2; 8000~9000ft (160hp)
Clicker 3; 9000~10000ft (155hp)
Clicker 4; 10000~11000ft (150hp)
Clicker 5; 11000~12000ft (145hp)

………………..seems pretty simple eh? If you have an overrev problem in a pull, really, it’s as simple as getting a spacer weight to put on the pivot bolt to correct engines speed.

• Law: IF need lower rpms, THEN add flyweight.
• Rule of thumb; 0.5grams = estimated 100 rpms change. 1.0 grams = estimated 200 rpms change.

.
Below is MY (model year) 2021.
I sorted out the grams for the 951, 994 and 903 on that spec sheet. (Ramp# + applicable pivot bolt)

Chris) clutch changes for the 2021 turbo sleds and how it will effect performance VS clutch kits over the 2020 models
Joe) nothing really. Regardless of 20.5 or 21 model, still has the same “convertor”, the same secondary clutch settings. They both have a 40 helix and 160/303 secondary spring.

I have a secondary force calculator (and its not the team one) for skidoo QRS secondary clutches.
When you apply a torque of 115 pounds from the 850 engine, the secondary converts estimated 856 pounds on the side of the belt at the start of the shift off of engagement to move the sled and 520 pounds at 1:1 clutch ratio. (belt at 7/8” from the rim of the primary clutch).

Ok with that being said…You can put a 951, 994, 903, 984, 990, 968, 967, 971, this guys clutch weight, that guys clutch weight and in the end, regardless of the weight of it, the secondary still will convert….

…….856 pounds on the side of the belt at the start of the shift off of engagement to move the sled and 520 pounds at 1:1 clutch ratio [until you change the spring force and/or helix angle(s)]

Here is an example of this or that guys clutch weight.
https://www.silberturbos.com/products/ski-doo-850-gen4-turbo-ramps
Silber has a 59.3 gram clutch weight. Hereinafter lets call it the STR (silber turbo ramp)

If you put that in with the standard pivots, 16.7 or 15.2 or (16.7+4.9 spacer) then you will underrev and have to clicker up to get correct engine speed. How much rpms would you lose by putting that weight in?
Lets do the 6000~10000 pivot setting.

STR @ 59.3 grams + 15.2 grams = 74.5 grams. Wait, the requirement for correct engine speed is 64.3 grams. (go back up to look at the brp spec)

Estimate engine speed loss from being over grams.
74.5g – 64.3 grams = 10.2 grams. Yeesh, at 1 gram = 200 rpms then you are looking at a 2000 rpms loss (in theory)
Q) How do we lose 10.2 grams? A) lighter pivot bolt and possible higher clicker number.
There is a 8.9 gram titanium bolt (25mm)

Then…
STR @ 59.3 grams + 8.9TI gram pivot = 68.2 grams. But we need to get into the 64.3 grams. 4 grams too heavy. There is a clicker adjustment we can do. IF a clicker can change 200 rpms, THEN have to change 4 clicker numbers.
Go from clicker 1 to 5 and that should be close to get 7900 rpms again.

Then…
Here is the complete 994 ramp cam arm assembly complete with factory parts including clicker adjuster. The overall weight is 85.7 grams.


Now lets look at a weight eliminating the clicker.


With this 82.7g SLP weight, you need to add more grams for it to be even with the BRP assembly @ 85.7 grams.
85.7g(BRP) – 82.7g(empty SLP) = 3 grams. You will be adding 3 grams of whatever setscrews or washers to make the ramp weigh the same as stock BRP @ 85.7 in clicker #1.

You go run the stock BRP weight at 85.7 grams in clicker 1. (has clicker adjustment)
You go run the STR weight at 89.5 grams in clicker 5 (has clicker adjustment)
You go run the SLP weight at 85.7 grams (no clicker adjustment)

….all 3 (in theory) should run at estimated 7900 rpms.

………and; when you apply a torque of 115 pounds from the 850 engine, the secondary converts 856 pounds on the side of the belt at the start of the shift off of engagement to move the sled and 520 pounds at 1:1 clutch ratio. (belt at 7/8” from the rim of the primary clutch) regardless of...

• BRP weight at 85.7 grams in clicker 1. (has clicker assembly adjustment) [makes 7900 full throttle]
• STR weight at 89.5 grams in clicker 5 (has clicker assembly adjustment) [makes 7900 full throttle]
• SLP weight at 85.7 grams (no clicker assembly adjustment) [makes 7900 full throttle]

….all 3 (in theory) should run at estimated 7900 rpms but you loop right back to “856 pounds to 520 pounds” because no matter how you push from the primary clutch with Moe or Larry or Curley’s ramps, you still convert “856 to 520” to the track from the secondary clutch.

This primary clutch weight over here, pulling on the belt with that secondary settings over there, is still going to produce 7900 rpms.
IF the weight is lighter, THEN you'll see more than 7900
IF the weight is heavier, THEN you'll see less than 7900
...the secondary settings are constant, you havent changed anything, regardless of 20.5 or 21.

Secondary clutch
The average secondary clutch setup is estimated 60% efficient. IF there is 160hp, THEN the secondary clutch converts estimated 96hp (40 helix + black spring)

You can put Moe/Larry/Curly's ramp or use whatever BRP ramp in your primary clutch.
A logic statement....
IF I fiddle with my secondary clutch settings to raise my efficiency from 60% to 64% by a different helix and/or spring force and optimize gearing, THEN no matter what you run in your primary; "me", with a stock ramp and correct pivot bolt weight matched to the secondary to achieve 7900, "you make the rules" and ill show up to race you.

hope that was alright...my eyes are buggy now.

 

[Dynamo^Joe]

• BRP weight at 85.7 grams in clicker 1. (has clicker assembly adjustment) [makes 7900 full throttle]
• STR weight at 89.5 grams in clicker 5 (has clicker assembly adjustment) [makes 7900 full throttle]
• SLP weight at 85.7 grams (no clicker assembly adjustment) [makes 7900 full throttle]

Based on 160/303 black secondary spring and 40 deg helix.

What will happen to 7900 IF change to a 37 deg helix or a 43 deg helix?
What will happen to 7900 IF change to a 43/37 deg helix or a reverse 43/47 or a reverse 41/47 helix or a 44/40 or 47/40 helix?

What will happen to 7900 IF change to a 160/220 secondary spring or a 180/303 secondary spring?

[leave gearing alone]

 

[turboetech]

Thx Joey now you have everyone’s attention

 

[Dynamo^Joe]

I just wanted to answer the question as best I can in a way that I dont make an opinion, rather bring forth some so-called facts that makes the reader think. This will give the reader the means to stave off the execution of someone's pre-programmed-prejudice on you. You know, like when you read someone say "its mandatory" or say calling BRP techs "gearing fools" or saying "too strong of spring" or "too much weight". When you read that kind of bent or bias decision making from someone else, there is a percentage of people who fall for those sh|tty conclusions.

Here is where i'll make an opinion (start opinion)
Guy bangs the gong "too much pivot weight".
Ok, you ask that person...What is too much weight?
Then say, Instead alleging "too much pivot weight", the facts constituting "too much weight" should be laid out and proven on weight here vs weight there. And then a line has to be drawn in the sand where "this amount of weight" is too much and "this amount of weight is not" and a line to show the two distinct weight values; can't have a grey area for "convenience" to make your case.

Q] what do you do when someone says "too much"?
A] Fkin run downtown rite now, and add more.

Q] what do you do when someone says "fools gear lower, you need to gear up"
A] tear into the gear case as fast as you can and gear lower, like i mean gear lower if you even gotta make a smaller gear out of chunk of steel with a chainsaw file. And then go test and learn what they dont know. And then when you have this experience under your belt; dont' tell that mouth, fk-all.
(end opinion) haha

So, there you go. Its just a bunch of numbers and tuning law and rule of thumb, so most of it is not my words. I just put it together.

I hope its genuinely positive in showing a logical means where the reader now, can go get any weight on the market, OEM or aftermarket and set it with the equivalent BRP grams as a launch point to tune.

thanks
joey

 

[NoBrakes!]

Canadian ta boot!