Gearing

 


Gearing - Mountain Specific
Gearing - Summit 800etec over revving on road
Gearing - Change track from 1.25 to 1.75

Gearing - Changed from 20 to 18 tooth and lost engine speed

 

Gearing - Mountain Specific

If you ever want to regear, it’s not a problem with this kit to go any of these ratios, in fact my helix’s work so well with lower gearing for whatever track speed you achieve, it will maintain it with great strength.  Lower gear; even stronger track speed holding power.

XP/XM Chassis
21:49 = 2.33 = 104P
19:45 = 2.36 = 102P
21:51 = 2.42 = 106P
20:49 = 2.45 = 104P
20:51 = 2.55 = 106P  
19:49 = 2.57 = 104P
19:51 = 2.68 = 106P

Rev chassis
19:45 = 2.36
19:46 = 2.42
19:47 = 2.47
19:50 = 2.63
19:51 = 2.68

 

Gearing - Summit 800etec over revving on road

Larry writes) I am running 21.5 grams of weight, on clicker 3, stock gearing, 20XX 800etec 154" summit.  
Testing was done on hardpack trail, initial rpm's WOT 7900, held the wot and started climbing in rpms after a period of time, until hitting the rev limiter.  1200 feet altitude, I was not able to get top speed reading.  

A couple of questions: 
1] Normal operation is not trail use, so I would not hold it WOT like I did for testing.  It took quite a while for rpms to start increasing under WOT.    All short WOT operation, small hills, midwest riding in UP of Michigan.  
2] Should I be testing in off trail conditions?

Moe writes) Hardpack is fine for going for a ride to see if there are any bugs or anything was installed incorrectly or needs to be adjusted.

The clutching is designed for getting more track speed in deep snow when breaking fresh snow and enhancing the backshift strength.  Breaking fresh snow, backshift much stronger and able to maintain full throttle in deep snow and have correct engine speed for long periods of time.  Continuous cycling of throttle with strong recovery.

 

Your sled is geared @ 19:49 so lets find out how fast the theoretical vehicle speed will be.

Far as going out on hardpack you’ll end up finding out what top end is real quick and when the clutches shift out the engine takes off into overrev.

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Sledders talk about overreving their lower geared sleds....
Questions to ask) When you hit the throttle from a dead stop, does the engine go to 84~8500 right away (yes or no)
IF no, then what engine speed does the tach go to when you punch the throttle?

When you are traveling along part throttle at 30~40mph and hit the throttle full, does the engine go to 84~8500 right away (yes or no)
IF no, then what engine speed does the tach go to when you punch the throttle?

What vehicle speed does the engine start to go past its rated engine speed?
Comment – what we are looking for is “When does the engine overrev?”
Right away in 10 feet or like 400 feet or more?

Next question - Is there any speed from 0kmh to 60mph that is less than 8500? Yes or no?
To prove the clutch shifted out and cannot stroke anymore - Go prove this yourself - Take a felt marker and mark the primary clutch.

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Now go take your full throttle run and watch the tachometer.  7900~8000~7900....and then eventually it starts to go over 8000 – STOP!
Pop the side panel and look where the felt marker was wiped off and now you have proof that you are expecting more out of your gear ratio than what your sled has for maximum speed.

Once the clutch achieves overdrive and stops stroking then...Adding flyweight is not going to stop overrevving from 8000 to 8500.  Lowering the clicker is not going to stop overrevving from 8000 to 8500.

The only way you will stop the overrev at the speed its been overrevving is to....

  • Gear up.  1 tooth will increase about 3.5mph theoretical top end.
  • Put the sled on the back of a truck
  • Falling off a cliff.  haha

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Gearing - Change track from 1.25 to 1.75

Question) Hi I was wondering if it would be better to go down two top gear teeth when taking out my 1.25” track and putting in a 1.75 on a xp 600 carburetor.  Does the little 600 carb have enough power without breaking belts to turn the 1.75 when you get into deeper snow?

I don't want to lose all the top end speed but I love playing in powder. When I ride with my father it's 80mph all-day and don't want to be W.O.T. all-day.

Answer) For every 1/4" increase of track lug height you could be gearing down at least 1 tooth on an 800.  On a 600 you can go 2 teeth down for every 1/4" of lug height increase.

2010 600 Carb gearing should be 25:45 with original 1.25 track.

The latest 600 Rene' BCX's geared at 21:49 (equivalent gear to 19:45 gears)

Going to the 120x1.75 track, I would at least run a 21 top gear with a 104P chain.

 

This is an important question(s) for any tuner - its right at the top of questions when changing a track lug size.
Question on top speed – what is the highest most reasonable peak vehicle speed you want to achieve with the new "X" size lug track?  Be sensible about the peak speed. 

Question - time at top speed - How much time do you spend at your highest vehicle speed chosen?  (When I say high, I mean from 3/4 speed to full speed of this potential vehicle speed you are being sensible about)  Is the time several seconds?  Just a quick shot to top end?  Several seconds?  30 or more?

Keep in mind the engine power you have.  A carburetor 600 is about 104~106hp and want to push a 1.75 track to 90+mph on GPS or Radar?  Going that fast is going to be difficult to uphold.  I'm not talking speedometer, rather talking GPS speed measurement.

There are 2 significant clutch ratio lines inside the clutches.  First is 1:1 clutch ratio.  The engine speed is the same as secondary shaft speed.  1:1 clutch ratio is roughly 3/4 of an inch from the rim of the primary.  Second is the outer rim of the primary.  From ¾ of an inch to the rim of the primary clutch, that is where the secondary shaft speed continuously increases speed over engine speed.  The secondary shaft can turn up to 17% faster than the engine. (Difficult to tune in this range)

image

The orange boxes show where the drive belt would be in the middle of the overdrive portion.  Those figures reveal where the drive belt is about 7/16 from the rim of the primary clutch.  To achieve top speed and uphold it, some conditions need to be met.  Good conditions are; correct snow lubrication, not deep snow, soft suspension settings, flat ground, not much wind, good fuel octane, good engine and clutch fitness.  With conditions met, one can achieve speed values in the orange boxes (middle of o.d.)

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Gearing - Changed from 20 to 18 tooth and lost engine speed

Matt writes) Trail clutch kit for my 06 MXZ x 600sdi. I re-geared to a 20-46, 1.75 track.

It is amazing the difference. I can beat most stock 800s to 80.

Lowered gears even further to 18-45

Comes out of the hole crazy fast, gained a bit top end speed.

Powder it hits 8000 then drops to 7000 and picks back up if I stay in the throttle.

Before I go back to the 20-46 gear set up is there anything I can do to leave that gear set up in? Like a ramp change or something.

 

Joe writes) What you can do is learn more about what gearing does in effect to the workings of the primary clutch.

One thing you will find from gearing down a substantial amount to measure, and I don't mean one tooth, I mean two teeth or more will make a substantial difference that you can feel in the seat-o-pants...
...The effect gearing down has on flyweight- Gearing down gives flyweight the motive to act like a heavier mass than previous gear. The fact is the Center of Gravity (hereinafter CofG) of the flyweight is now at a farther relative position away from the clutch shaft centerline per mph/shift position on the shift curve.

For lack of better numbers lets use 90mph and pick the difference between 18 gear and 20 top gear.
*Where is the belt centerline on the primary clutch face at this steady mph?

At previous gearing [20] the belt centerline and the CofG position of the TRA arm is lower and closer to the clutch shaft or if you like..the engagement position. When depressing the fuel to accelerate, you'll find the engine will shift at whatever rpm and peak at the proper rpms.

With the newer lower gear [18] the belt centerline and the CofG position of the TRA arm is higher and farther away from the clutch shaft or if you like..the engagement position.

NOTE - IN THE PICTURE LOOK WHERE THE BELT IS NOW WITH THE 18 GEAR(RIGHT) VS. 20 GEAR(LEFT)

image

When pressing the throttle to accelerate, you'll find the engine will shift at a lower rpm than the 20 gear and the peak rpm will be slightly less than proper rpms. You could lose 100 rpm or more because the weight is heavier and pushing harder at the 90mph speed.

Now there are a few advantages to this. From rest, as the sled speed increases, what inevitably follows is the flyweight does more work. The primary will capture slightly more the "meat" of the torque curve, especially on trail where you are on and off the throttle. The flyweight is taking advantage of a cooler exh pipe which some know that a cooler pipe makes more torque at lower midrange rpms.

NOTE: WHEN GEARING DOWN THE LEVER WILL BE IN A HIGHER POSITION ON THE RAMP - DOING MORE WORK AND ENGINE SPEED LOSS MAY  RESULT - and can cure with a spring end force change.

I always get nearly the same comments that tuners can get a higher mph cresting the top of a hill and holding the skis in the air longer up hills. More torque going over the hill and especially when letting off the throttle to go thru the bottom safely, they ascend back up another hll, the engine is right there, responsive with improvement to get to peak rpms.
And nearly always recording the same top speeds on hardpack light loaded road conditions.

Clutch kit specs

Ramps – 410

Primary spring – 200/350

Secondary spring – 231/303

 

Matt writes) Powder it hits 8000 then drops to 7000 and picks back up if I stay in the throttle.

Joe writes) Aaen says IF engine speed drops towards top end speed, THEN raise primary spring end force.

Take the primary spring end force and raise it.  Go from the 200/350 to a 200/380.  That will raise engine speed where you were losing down to 7000 rpms.

There are no other springs from BRP that have a start at 200 with a higher finish than 380.

The next spring is the straightlineperformance.com BLUE 190/420 or the RED 220/420

If you do not want to source those springs you can also raise the finish force in the secondary spring

The Dalton Yellow/Orange 225/330 is a good choice too.

 

So if you still have fluctuating engine speed with the 200/380 primary spring

Then can change to a higher final force primary spring

OR

Leave the 200/380 in the primary and add the secondary spring with a higher end force 225/330 as mentioned.

Thanks, joey

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