December 2015 Ask the Experts

Track modifications, dyno testing, cylinders and clutches ... oh my!
1996 Polaris XCR 600
The 1996 XCR 600 was built for Polaris “performance-minded riders.”
Drop and Roll?
Q: I am going to put a bigger lug on my Polaris wedge chassis, so I am wondering if this chassis will take a 1.5- or 1.75-inch lug without any modifications, or will I have to do a drop-and-roll chaincase to accept the big lug? The chassis is a 1996 XCR 600. – polaris680

A: With the 1.5-inch lugged track, you will need to change to 8-tooth drive sprockets on the driveshaft. The smaller sprocket will gear the sled down about the right amount for proper performance in deep snow. You will also need a tunnel extension and rail extensions to complete this conversion if you are going with a longer length track.

With the 1.75-inch lugged track, 7-tooth drivers will be necessary. Again, the smaller sprocket will gear it down about the amount that is needed for this taller lug track. A tunnel extension and a pair of rail extensions, again, will complete this build if you are going with a longer track.

If you drop and roll the chaincase, you will be able to use the stock 9-tooth drivers with either track. The gearing in the chaincase will have to be changed to accommodate the more aggressive track. – Jerry Mathews, Starting Line Products

Reader Responses: Cylinders & Clutches

Q: 800 Polaris Storm Cylinders Can you put the older steel sleeve cylinders on a newer motor that had the Nikasil cylinders on it? I came across a ported big bore top end that was the steel sleeve version and wanted to put it on my bottom end. – Dragbanshee23

A: Take it from me, sleeved big bore cylinders on a Storm bottom are not worth the effort, that’s just my opinion. If you ever get them to seal without leaking coolant, you should start a club ... you might be the only member! My advice: find some good Nikasil cylinders or leave it stock. The problem is that the sleeves, by design and size limitations, don’t have enough support behind the O-ring and will break. There is no repairing the broken sleeve tops. – chines

Q: T-Cat Clutching I have a stock secondary with an 8.5-inch primary. The center-to-center is set a bit shorter than stock to allow shift (bought it this way, assume that’s correct). The helix is machined to allow OD. I want to machine a nice center-to-center gauge. Using a stock length belt, what should I set the distance at? – fastcar01

A: I would pull the springs out of the clutches. Close the primary and open the secondary so you get the correct deflection when belt is installed at full shift out by moving the engine back and forth. This should be the new C-to-C. Record the belt length and buy that length belt next time for that new C-to-C distance. Adjust your belt deflection at rest with springs installed with washers in secondary clutch. – tcat446
snowmobile dyno test
Dyno Difference
Q: I’d like to have my sled dyno tested, but I’m not sure if I should use an engine dyno or a track dyno. What’s the difference? – phddrifter3

A: The name says it all! The engine dyno measures the horsepower, torque, etc., that your engine puts out. It’s a great way to determine how different variables (temperature, airflow and more) affect your engine’s performance. You can also see how different engine performance products (turbos, superchargers, etc.) enhance your engine’s power output.

A track dyno measures the amount of power being transferred to the surface you’re riding on. Power to the snow is what wins races! It’s why sleds with lower engine HP numbers can be quicker down the track than another sled with higher engine HP numbers. It’s also where you can really start fine tuning your machine with clutching, gearing, jetting and more to figure out the exact setup that gets you the most power to the ground.

In either case, it’s extremely important that your sled be in good running order before you bring it to your local dyno shop in order for you to get your money’s worth. A dyno session is not the time for maintenance! There are a lot more nuances between these two types of dynos. No worries though, we’ll have more on this subject in an upcoming issue of American Snowmobiler! – Experts   

Experts Challenged on HP
Got your latest issue (Oct. 2015). The horsepower numbers you gave on the AXYS 800 H.O. are low and wrong. We dynoed six of them and they range from 152-156 HP. Get your facts right before you publish! – Brad, London, Ont.

A: Brad, thanks for reading so closely! We’ve had this particular engine dynoed several times, and on different dynos, so we don’t doubt your findings on your own particular dyno. Both DynoTech Research in Batavia, N.Y., and Aaen Performance in Racine, Wis., have done dynos on this sled, along with AmSnow. We always take our published HP numbers from third-party independent dyno shops (in this case, the stats were from DynoTech Research, which does much of our dyno testing for the season, prior to our New York Shootout).

It’s important to note that these published HP numbers were taken from a sled that had not been through the extended OEM break-in process. At the New York Shootout, we take an “out-of-the-box” measurement, which often accounts for lower HP numbers on the dyno, but it’s the only way we can ensure a dyno measurement without any tampering from the manufacturers or performance shops for this event. Basically, we want to keep a level playing field across all the manufacturers since they all have new sleds at this event.

In addition, we published an article on this Polaris engine in our January 2015 issue (p.22) showing the HP post break-in,  which was exactly in line with your findings. – Experts
2016 Ski-Doo MXZ Blizzard
It's Blizzard season!  Ski-Doo’s 2016 MXZ Blizzard offers the option of a pre-studded Ice Ripper XT track.
More Track Advice
I’m thinking of studding my track or upgrading to a pre-studded track this season. Which do you prefer for trail riding and why: Non-studded track, pre-studded tracks, or adding aftermarket studs to your track? – Skidoobyyou

A: Like most of the answers we give,  this one depends on your style of riding and trail conditions. Our personal favorite is still a track outfitted with aftermarket studs. It provides the most control in the widest variety of conditions. One downside to studding your track is that it adds weight, and it isn’t much fun to install them yourself, as you’re bound to spend several hours in the shop. Side effects might include an aching back and a few busted knuckles from the install. Traditional studs also aren’t cheap.

We are also pleasantly surprised by the effectiveness of pre-studded tracks, such as the Ice Ripper XT on Ski-Doo’s 2016 MXZ Blizzard, which we trail tested recently in some severely icy conditions. The performance of the pre-studded tracks we tested were a step up from a non-studded track, but they do not afford you the same luxuries during hard braking situations, or controlling your sled when it starts to slide, as aftermarket studs typically do.

Track technology has certainly come a long way since the early days of snowmobiles. It’s absolutely possible to not stud your track and get great performance on the trail with today’s tracks. You may actually find the non-studded track forces you to be a better rider by making you account for longer stopping distances and more slide in tight, icy corners. That’s not necessarily a bad thing. Our preference is still for the aftermarket stud-installed track, but the debate will likely continue!”  – Experts
FOX mountain trail sled shocks
FOX's mountain sled shocks (left) and trail shocks (right) are visibly different.
Did you know ...
FOX has a different standard diameter for its shocks based on whether you ride in the mountains or the trails. The trail sled shocks feature a 2-inch diameter bore, while the mountain sled shocks have a 1.5-inch diameter bore.

The larger diameter offers more volume, which equates to more comfort for the constant performance demands from bumpy trails. The 2-inch diameter also allows better control over the shim stack in the shock. The concept of a larger diameter shock bore is used extensively by FOX in its side-by-side vehicle product development.

The smaller 1.5-inch shock bore for the mountains saves weight in a riding scenario where fractions of a pound matter. The shocks also do not face the same constantly high demands as the trails when floating through powder and operating at much slower average speeds.
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