Previously you had three choices:
Do nothing. -
Run a seven-tooth driver: The diameter of a seven-tooth driver is 6.7”. The diameter of the nine-tooth 2.52” pitch driver that you had stock is 7.2”. If you chose to run a seven-tooth driver, your approach angle will increase six degrees. We have all been going to eight inch or even nine-inch rear idlers to reduce the rolling resistance of the track. Going to a 6.7” driver would be counter productive. The space between the track and the bulkhead is very close. You might have to run your track tighter than you want. If the track climbs out on the anti-ratchet teeth and hits the tunnel without disengaging from the anti-ratchet teeth, you could spin the driver hubs or worse.
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Roll the chaincase: If you roll the chaincase, you can use an eight-tooth driver. Its diameter is 8.65” (including the points) and it radius is 4.32”. Using a stock chaincase, the distance from the center of the drive shaft to the outside edge of the jackshaft is 7.25”. A 2.5” track is 2.75” thick, including the belting. Adding the radius of the eight-tooth driver and the thickness of the track, you get a little over 7”. There is barely enough distance between the two shafts to let the track ratchet and not hit the jackshaft. Once again, you might have to run the track a little tighter than you would like.
You now have a fourth choice. Install our extended chaincase. The measurement between the shafts is 9.25”. We use the stock mounting holes. It is easy to install. The secondary clutch and jackshaft remain in their stock location. That makes it easier to get the drive belt on and off. There is over .5” clearance from the 3” tracks and the tunnel, even when using an 8 tooth, three inch pitch drivers. The ice and snow that the track carries forward, can easily flow thru the front of the tunnel.
All of these units relocate the drive shaft down and back 1". You can run a 3" paddle track with an eight tooth driver on all of these sleds. Your approach angle will decrease up to 13 degrees. The jackshaft and secondary clutch stays in the stock position. There is lots of room for snow evacuation.
Over the years I've read various performance articles, each one promoting the writer's views. I guess that it is my turn, so here goes.
First of all, I live and ride in NW Montana. We usually have about 150 inches of snow at the elevations we ride, moderate hills and lots of trees. It is a lot like Revelstoke and Golden B.C., but with trees. I'm lucky in that I can ride my sled from the house.
The first and most important performance tip that I can give you is have a reliable sled. This is especially important to those of you who are only able to get out 10 or so times a year. Driving for hours to get to the snow and having snowmobile maintenance clinics in the woods is no fun for you or your friends.
There are lots of engine modifications you can get. Some of them work very well and some don't. They all try to get more power out of the stock engine. Whenever you get more power out of an engine there is more wear and shorter life. I have some modified motors and I'm willing to accept the additional maintenance risks, but they are always there. Without going to the expense of a turbo or supercharger, you will have an increase of about 10%.
Total sled weight can be an issue. The less weight an engine has to move the faster the sled will accelerate with the same horsepower/traction. The operational weight of a light sled is around 700 pounds (sled 450, fuel and fluids 100, driver and gear 150-200 pounds). It is relatively easy to lose 15 or 20 pounds on a stock sled. An aftermarket exhaust canister will usually do that with a cost of $400-$500. Total operating weight reduction is less than 3%. Losing additional weight is harder and more expensive, about $100 a pound.
It is my view that having the proper track for your conditions is the smartest and most economical method of improving the performance of your sled. Your track transfers your horsepower to the snow. Efficient interaction between the snow and your track is vital.
First of all I'd like to address a couple of myths about tracks. You need a big motor to move a bigger heavier track, wrong. A track is a big conveyor belt. The engine has to overcome the drag of the clutches, bearings in the chain case and bogey wheels. Bending the track around the drivers and idlers also creates drag. If you go from a 155" track to a 174", the distance from the drivers to the rear idlers is increased about 9 inches. System drag doesn't increase, just because there is more distance between the drivers and rear idlers. Granted, accelerating a heavier track from zero to 50 MPH will take a longer time as compared to a lighter one. If it takes 10 seconds to accelerate a 60 pound 155" track to 50 MPH, it will take about 20% longer to accelerate a 72 pound 174" track, an extra 2 seconds. That delay will hardly be noticeable. What will be notable will be the acceleration the bigger track has over the smaller one.
A sled will accelerate as long as the track can push against the snow and the snow stays put. Except in very hard snow conditions there is always some track slippage. For each snow condition there is a point where the snow starts to give and move rearward, forward momentum is lost and the rear end starts to sink. We want to use horsepower to move a sled forward, not push snow backward.
Obviously, it is the track's paddles that push against the snow, the more square inches of paddles, the better. My personal shed has a 174X16X3" track on it. There are 21 rows of paddles on the ground, not counting the track leaving the drivers to the rails. I have 528 sq. inches of paddles to move my sled. Using the same logic, a 163X16X2.25" track has 358 sq. inches. A 155X15X2.25 has fewer than 300.
I have been told that it takes twice as much horsepower to climb a 30 degree slope at 40 MPH as it does on the flat. We all have machines with enough horse power to go at least 40 up a 30 degree slope. The problem is that there are times that the track can't transfer this power to the snow. Once the snow starts to give, you are going to slow down. When you slow down the track starts to dig a trench. If you are trenching, you're rear suspension sinks. You are now climbing a steeper hill. That steeper hill requires more horse power and the trenching increases until either you turn out or are stuck. In every situation, my 174 track has about half the paddle loading of the 155 and I will have to turn out later, if at all.
To sum this up, if someone came to me and asked me to race an Olympic swimmer, what would I do? I could lose weight, start a fitness program, or buy big swim fins. Which one makes the most sense to you?
Order yours today and be prepared for the deep snow this winter. |
