Flyweight - Going from stock engine to big bore, change flyweight?

Flyweight - Going from 800etec to 872etec

Flyweight - Can I run a calibration from 2000' to 10000'

Flyweight - Exhaust - Adding a pipe and/or y-pipe

Flyweight - Recommended grams are different than what's in the flyweight kit

Flyweight - Going from stock engine to big bore, change flyweight?

Question) Have your clutch kit on stock 800R x 154".  15.3g for 8150, clicker 4.  Dropping in 860BB. Currently have your mountain kit installed.  What do you recommend for a set up for this kit at 6000 feet, spring change, pin weight, ramps?

Answer) Your carbureted 860 kit needs correct jetting before the engine speed will have a chance to be correct. 
You’ll find the full throttle engine won't be near its suggested rated speed until 2 main jet sizes away from target.  The tuner first must achieve correct carburetor jetting to get the engine calibrated properly.   Then start to tune the primary clutch to match the correct engine calibration.

At this point don't change the clutching other than a clicker choice.  Push off the dock with the new engine and get your sea legs with it.  Make sure you have the confidence its going to rpm correctly and actually make the power its supposedly to deliver.

Don’t be fooled by more power = more flyweight.  More pinweight is needed, if the engine runs with increased torque at the original 8200 engine speed or lower.

Example) my test guy FastZap, dyno’d his 800R at 150hp at 8150 rpms.  After getting the big bore dialed in and dyno’d it, it went to 169hp at 8300 and had to increase 2 grams but there was an honest 19hp increase.

Another of my test guys went to 8500 twins with his big bore.  Clutch settings from (16 grams @ clicker #4) to (15grams @ clicker #5 to get 8500).  Sled very strong and higher track speed.

Aaen's Principle) Weight determines rpms.  IF you need more engine speed, THEN reduce the flyweight.

IF need less engine speed, THEN increase the flyweight. 

1 gram = approximate 200 rpms engine speed change - All testing is done at full throttle.

Bring your tools to change pinweight if needed.


Flyweight - Going from 800etec to 872etec

My personal sled is a 2013 TNT 800E x 120 x 2" paddle w/19:49 gearing (yes a short track w/154 gearing haha)

The flyweight for my stock engine was at 21.5 grams in clicker 3 for 7900~8000 rpms.  After installing the TRYGSTAD 872, the first test I did was over revving at 8200 with the 800 settings.  To overcome high engine speed, I selected clicker 2 to get 8000 rpms.  The sled pulled much harder.  At the moment, Im not happy with the backshift in some moments when cutting deep snow. 

The lower clicker number revealing 8000 rpms told me that I can add at least 1 gram of flyweight (get back to clicker #3.) 

Knowing that 1 clicker number = estimated 200 rpms change.  Knowing 0.5 grams = estimated 100 rpms change.  I wanted to make the engine grunt at 7900 and just touch 8000.

I added 1.5 grams and reset to clicker #3 and now I get 7900~8000 and there is a big increase of pull on my arms.  Wanting to see how much harder I can load the engine, I removed the 167/390 and installed a 135/385, lowering the start force of the primary spring. 

The engine pulls even harder now off the bottom end and backshift is superb.  The 872 pulls harder and maintains track speed with more attitude than before.  The proof of more torque at 7900 with the 872 than the original 800 is the flyweight grams I had to add to prevent an overrev

Flyweight - Can I run a calibration from 2000' to 10000'

Question) is any clutch kit or calibration able to cover 2000 to 10000 feet, or is that too big of a gap?

Answer) First off lets analyze the engine HP per elevations.  The percentage noted is information from a Rotax Aircraft engine shop manual.
100% @ 0000' elevation [150hp]
89% @ 3280' elevation [136hp]
78% @ 6560' elevation [121hp]
60% @ 9850' elevation [102hp]

Example engine – mild ported 800HO rated @ 7950 rpms.  At 2000 feet there is an estimated 144hp.  You have clutch settings that work with an estimated 6hp difference from 144hp that allow the engine to run at its +/- 100 rpms.

Flyweight used to get 7950~8000 rpms @ 2000 feet is 21 grams in clicker #3.

(150hp at 1000 feet – 144hp at 2000 feet – 138hp 3000 feet)  Ideally you should be able to run from 1000 to 3000 feet and not have to change the clicker.  The clutch settings should cover the variation in engine power and not go past the factory +/- 100 rpms allowable engine speed variation.

IF you go to 10000 feet [102hp] with that 2000 foot flyweight setting, the grams will be too much for the low power.  The ported 800HO has the power of a stock carbureted 500SS engine or a really strong 440.

Flyweight rule of thumb – For every 1000 feet elevation increase, then reduce one gram of flyweight.

Estimated flyweight grams needed for 10000 feet.  (10000 – 2000) = 8000 feet difference.

For 8000 foot difference, then reduce 8 grams from 21 = 13 grams.

You could be happy with your performance at home, but not happy with the performance out west at elevations.
At this point, calibration decision is based on a deficiency.  To overcome the power deficiency, the tuner has to change at least the flyweight gram amount for the higher elevation.

BRP supplies calibrations for different elevations, so do clutch kit manufacturers.  Its not as simple as changing a clicker for a 4000' elevation increase and expect near 100% performance.
Choices - install BRP high elevation components when you go to the mountains and then remove those components and run stock calibration back at home.
Run an all-elevation clutch kit so you can have the aftermarket capacity at home, however require that you only have to change the primary clutch flyweight for the elevations and power differences.

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Exhaust - Adding a pipe and/or y-pipe
Question) I have an exhaust that runs higher engine speed.   The exhaust is supposed to make another 10 hp now.  Should I add flyweight for the additional horsepower?

Answer)Say with stock engine you run 8150 rpms. Add an exhaust system and now the vendor wants you to run 8300. The additional hp is by virtue of engine speed increase and now not necessarily have to add more flyweight.

Remember the principle about finding rpms - IF need higher rpms, THEN reduce flyweight.

IF the engine is making 10 more HP at the original engine speed, THEN you will have to add flyweight grams.  The engine is making more torque at the original engine speed now and yes you will have to add a percent more grams to maintain original engine speed.

IF the engine is making 10 more HP at higher than original engine speed, THEN you will have to reduce flyweight grams.  The engine is making less torque now at the original engine speed.  The HP peak speed is moved higher.  To get the engine to run at the higher speed, you will have to reduce flyweight. 

Better to run the sled first, observe rpms, what are they? Then make a clicker adjustment to see if you can find the new engine speed.  If you were able to prove the engine ran better at the higher engine speed with the higher clicker number then can reduce flyweight and get back to the original clicker number.

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Flyweight - Recommended grams are different than what's in the flyweight kit

Question) I received my kit.  From the weight instructions 21.5g is the wanted starting point for my elevation.  Referencing the tungsten rods sheet the closest setup is 21.6g (14.5 + 6.3 slug + .08 set screw).  Is this 21.6 gram what I should put in or do I need to remove 0.1gram to make it 21.5 grams?

If I do need to remove small gram increments like 0.1g for tuning purposes, what is the recommended way to do so? 

For example would I take a file to the tungsten rods or sand down or file down the set screw ends to reduce small amounts of grams.

Answer) Hi.  Don’t worry about the 0.1 gram. 

½ gram = estimated 100 rpms.

The parts in the flyweight kit are spaced with enough estimated ½ grams for you to achieve the needed engine speed if needed to change engine speed.

Don’t worry about 0.1 gram because one can’t even frame a test to offer repeatable results of engine speed change with 0.1 grams.

You have to start with an estimated flyweight setting.  From that point on it's you and the sled and the environment you’ll run it in – the tachometer will speak to you if the engine speed is correct or not.

Each sled is an individual when it comes to fuel type, compression, suspension settings, where you stand or sit on the sled, snow type, all local to where you are riding. 

Put in an estimated amount and go test full throttle when you have the conditions to do so.  Adjust the engine speed with the flyweight grams.

Engine speed

Principles: *Flyweight determines rpms.

  • Need more rpms = Reduce flyweight mass.
  • Need less rpms = Add flyweight mass.

1 gram = estimated 200 rpms change at full throttle.