1985 Ski-Doo Formula Plus

July 21, 2009
Filed under Ski-Doo, Vintage Sleds

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1985 Ski-Doo Formula PlusThe early morning stillness was pierced by the sharp rap of a two- stroke engine spitting spent fuel. The familiar rat-a-tat-tat further told the experienced ear that this was the mighty rotary-valve Rotax engine stretching its innards.

Without looking, one would swear that a Ski-Doo Blizzard 9700 was cranking up. But there wasn’t a 9700 competing in Shoot-Out V. However, there WAS a brand spanking new Formula Plus preparing to do battle against the Indy, Tiger and Manta.

Indeed, the 521-liquid Rotax found in the 9700 does grace the underhood cavity of the Formula Plus (with a few changes, like a new pipe, to dial up the power just a tad more). The raw power produced by the 9700 always was that sled’s strongest suit. Where the mightiest of the Blizzards suffered in comparison to other go-fast rockets was in the chassis — it needed to add an IFS and subtract some bulk.

And that is exactly the FORMULA Ski-Doo came up with: the 521 Rotax, PLUS an IFS in a sleek new chassis. This is essentially the same chassis that Gerard Karpik and his cross country race crew has spent the past three seasons perfecting — with victories at such prestigious racing arenas as Alexandria, Eagle River and Sault Ste. Marie to its credit. Last season, Karpik concentrated on R&D and 50 Formulas were sent into the field to be raced by such throttle-to- the-bars jockeys as Todd Elmer and Lee Falck.

So, just how well did Ski-Doo pull off the transition from the track to the consumer version?

Well, first in the handling portion, second by a whisker in the acceleration phase and enough points overall to be crowned the winner of Shoot-Out V tells us that not too much was lost in the translation!

Key ingredients of the Formula Plus are the new suspensions — front and rear. At first glance, some may comment that the Ski-Doo system reminds them of the Polaris Indy IFS. Although there are some similarities, there are some notable differences. It’s true that both have coil-over-shock dampening. And the long bars running from the ski spindles to midway up the chassis on either side is common to both. A major departure in the Ski-Doo design compared to the Indy is the integration of the coil/shocks under the hood where they don’t interrupt the snow-planing characteristics of the bellypan.

The Ski-Doo system, like the Indy’s front end, boasts dual radius rods with the lower “rod” actually being an aluminum beam member on the Formula. There also is a torsion bar on the Ski-Doo IFS, as there is on the Indy, to add high speed cornering stability and agility.

A major difference on the Formula is a beIl-crank system that varies the leverage ratio of the ski over the shock absorber. What this means is that the suspension can absorb progressively more force or resistance, such as bumps and moguls, without bottoming out. It is the first mechanical (as in leverage ratio) progressively rising rate design that we know of on a snowmobile.

In plain English, when the going gets rougher, the suspension gets tougher. This is an important development in front suspensions because, so far, the IFS versions on the market have had essentially linear rate suspension systems. This means that the spring would flex by a specific amount for each and every inch of travel. The Formula IFS has varying rates of compression — meaning it flexes more easily initially and becomes more difficult to compress as the bumps get bigger. The progressive rate system gives the Ski-Doo a wider range, which simply means it can respond better to smaller bumps AND larger bumps than linear rate IFS.

The rear suspension in the Formula Plus is a new, race-bred design. In many ways, Karpik & Co. takes greatest pride in this portion of the sled. There are three coilover-Shocks in the skid frame—one up front and two in the rear. The rear suspension provides the driver with a multitude of choices in setting the suspension to perform under almost any condition — from competition to Sunday afternoon trail riding, It also allows for a greater balance between front and rear.

Exciting? You bet. I had my first chance to drive a Formula model the third weekend of January in full race dress — T handlebars, stiff-hybrid suspension settings, etc. Of course, I’ve had a chance to ride the Indys, V-Maxs and Tigers over the years and my initial impression of the new Formula was: impressive. Three weeks later, in mid- February, I had a second chance to ride a Formula in Valcourt, Quebec. We had miles of beautifully groomed trails to stretch out on. My impression of the sled was further enhanced. The Formula squirts around corners in a flat plane and the Rotax provides more power than you’ll ever really be able to use in the straights.

On both occasions, the Formulas I rode were the MX variety with the 463- liquid rotary valve. These machines had gobs of mid-range grunt and, really, had all the top end any sane snowmobiler would care to have at arm’s length. With that in mind, I kept wondering just what sort of beast would this be with the 521cc Rotax? Would it pull my arms out of their sockets?

Then came the first week of March and the annual Snow Goer tests and Shoot- Out. This was my chance to ride the Formula again, but this time with the 521, mega-horsepower Rotax. Handling characteristics are essentially the same on both sleds because the chassis are identical and there is virtually no weight difference between the two engines. Therefore, the only real difference is the silver paint on the Plus and half again more pony-power. At the end of your right thumb are a pair of 40mm Mikuni sliders just waiting to obey your every command and fulfill every one of your snowmo-fantasies. Sound awesome? Does it get your blood running a little hotter? It should!

Ski-Doo really has done its homework on this model. About 10 years ago, there was the notorious ‘Silver Bullet” from Ski-Doo. I had one. It was damn fast. But it suffered in cornering and rideability. The Formula Plus is everything the old Silver Bullet was supposed to be and light years more. The front and rear suspensions on this sled make it a match for any sled now on the market — and that means the Indys, V-Maxs and Tigers.

On the hard-pack trails at our north- woods test site, the Formula proved to be everything I anticipated in flat-out power. Mid-range was particularly impressive. The Formula Plus I rode had carbides on the front but no studs in the track. If I ever were to purchase a Plus, I’d remedy that situation immediately with some rear- end grip. Frankly, it was damn hard to keep the back end from spinning. I thought it was a crying shame to have seemingly limitless power that I couldn’t tap. Even one row of studs down the middle would have made a world of difference.

Under ideal conditions at the Shoot- Out, which included a plowed ice surface and a 25 MPH tailwind, the Formula Plus cracked the elusive century mark. We’re not promising that you will hit that right out of the box, but we’re confident that it is not out of reach.

Taking a peek under the hood, you’ll find that the Formula offers capacitor discharge ignition for hot sparks and fast starts. Oil is mixed with the fuel via an injection pump. And hauling it all in at the end of the lake is a self-adjusting, mechanical disc brake.

The Formula finished a few ticks and an MPH or so behind the Indy 600 in flat- out speed at our Shoot-Out. Our thoughts here were that the two machines could be compared to a match-up between the Ford Mustang and the Chevy Camaro Z-28 — one day one may win and the next day it could be the other. At the one-eighth mile, the two are, for all intents and purposes, dead even. It seems to us that the driver most diligent in prep and set-up may be the one drinking the other guy’s beer!

We’re certain that there are going to be some very interesting trail chases this winter. After years of having the power, this year Ski-Doo also has the glory via its victory in Shoot-Out V. And what all this means, essentially, is that the Ski-Doo faithful has some top quality ammunition for the coming season — finally.

Watch Out!

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