Flashback: The 1985 Ski-Doo Formula Plus Snowmobile

Although Bombardier was the inventor of the recreational snowmobile, the brand was slow to embrace the coil spring front suspension that revolutionized the sport.

The brand’s first attempt, the ponderous and trail-bound 1981 Blizzard 5500 MX, was late to the market and was definitely not a performance machine. It failed to find many buyers. Polaris and Yamaha had jumped ahead with high performance “independent” front suspension (IFS) sleds and Arctic Cat was just getting restarted, but go-fast Ski-Doo riders had to be content with the increasingly outdated Blizzard 9500 & 9700 leaf spring series that just was not very competitive with other brands on numerous points of comparison.

By 1985 Bombardier was finally ready to introduce its first high performance IFS sled, the Formula Plus. The product of three years of development by the Gerard Karpik cross-country race team, with about 50 pre-production units raced by Todd Elmer, Lee Falck and several others in 1984, it was definitely different. It was positioned at the top end of the multi-model Formula series, which also included leaf spring sleds.

(Editor’s Note: This article first appeared in the December 2022 issue of Snow Goer magazine. Click here to subscribe.)

The Performance ’Doo Reinvented

The sled’s all-new chassis had an aluminum tunnel with a front subframe of high strength low alloy (HSLA) steel tubing. Flexible Surlyn plastic was used for the belly pan and nose cone, but there was no front bumper. A magnesium chain case was exclusive to the Formula Plus, and it shaved more than three pounds of weight compared to the chain case found in other Formula models. The Plus also got a 16.5-inch wide track for better bite than the 15-inch track on the less-powerful Formula MX.

Formula Plus go-power came from an evolved 9700 engine featuring a new head, revised pipe and the convenience of oil injection for the first time on a high-performance ’Doo. Premium gas, 92 octane or better, was required.

This 521cc Type 537 Rotax produced about the same power as the earlier version, but with more low-end torque. A revised crankcase allowed it to be mounted lower in the chassis to lower the sled’s center-of-gravity for improved handling. And the 10.8-gallon gas tank was the largest in its class, providing the most range.

But the real story was about the suspension technology, with both ends using internal springing with rising rate geometry to improve the ride and streamline the overall form.

The front end used a cousin of the sprint car-derived Indy suspension but with a major twist. The coil-over-shock assemblies were mounted inside the belly pan so they would not drag in the snow. Operating through a bell crank on each side, they provided the same function as the external coil-over units on the now familiar Indy front end. It was the first progressively rising rate ski suspension on a snowmobile.

In back, the new Progressive Reaction Suspension (PRS) skid frame had three coil-over-shock units inside the tunnel. It offered six inches of progressive rate travel and more adjustability than competitive skids.

Winning Intro

Snow Goer held its fifth annual Muscle Sled Shoot-Out on February 28, 1984, at the Lakewoods Resort on Lake Namekagon near Cable, Wisconsin. Competitors were the reigning champ Polaris Indy 600 triple, the new Formula Plus, the equally new Arctic Cat El Tigré AFS 500 and the trail Manta twin-track enclosed machine with the same Suzuki 500 water burner as in the El Tigré. Yamaha declined to enter its V-max 540. At this point in the snowmobile industry, no other brands remained alive besides Bombardier’s Moto-Ski, now in its last season and down to one lone and definitely non-performance leaf spring model.

The Shoot-Out consisted of various timed acceleration and handling events with points awarded according to finishing positions. Each factory supplied its own driver, set-up and tuning. And each machine was torn down afterward and certified Stock by Snow Goer personnel.

When it was all over, the Indy 600 had won the acceleration phase again, but with the Formula Plus a close second. The Plus won the handling phase, with the Manta second. So, the Formula Plus was declared the overall winner on total points, with the Indy second overall.

A Few Problems Solved

Like most new models, Formula Plus and MX sleds reaching consumers had some issues.

The ski suspensions were typically stiff and failed to match many owners’ ride expectations, including my now-departed snowmobile club buddy Don Easterly. A mechanical engineer by training and profession, Easterly disassembled the ski suspension on his Plus, cleaned up all the tolerances at rotational points, and then re-assembled it. The ski suspension worked just fine after that rebuild and he was subsequently very pleased with the sled.

A few other issues like track clip shedding were also worked out and the Plus became a solid seller that returned Ski-Doo to prominence in the muscle sled wars. And today this is very collectable model that deserves more attention than it gets.  

Editor’s Note: Every Snow Goer issue includes in-depth sled reports and comparisons, aftermarket gear and accessories reviews, riding destination articles, do-it-yourself repair information, snowmobile technology and more. Subscribe to Snow Goer now to receive print and/or digital issues.