1991 skidoo mach i

When you think of power sleds, you think speed and acceleration. The 1991 Ski-Doo Mach I has that. It also has the most sophistication of any big-engined machine we've seen in a long, long time.

Bombardier engineers are very pleased with the 1991 Mach I, but they also are being a bit coy about its performance. Maybe they should be less coy. Consider that the new 617cc "long stroke" Rotax twin has a 10 percent power gain over last year's 580cc twin. That engine kicked out about 100 horsepower. Therefore, simple math tells you the 617 will deliver about 110 horses - about nine more than the Polaris fuel injected RXL.

We don't know that the new "long stroke" Mach I twin will blow away a fuel injected Indy 650 RXL, but the power is there.

We do know that the Mach I lets you add the luxury of electric starting, enjoy wind-tunnel tested styling, treats you to premium touring, and that it should be close in those big bore battles out on the lake.

We like the 1991 Ski-Doo Mach I. It is an excellent example of what we think the new performance snowmobile should be. Top speed and brutal acceleration are important if you are a racer. If you are a trail rider with a yen for speed, the Mach I is perfect.

Bombardier builds Quebec-style snowmobiles better than any other sled maker. It should, its engineers spend long hours on those freeway-like trails around Valcourt, Quebec, establishing performance parameters for its Ski-Doos of the future. In case you haven't noticed, North America's snowmobilers have gotten more and more spoiled by the annual addition of more and more kilometers of groomed and maintained trails. This concept of unified, interconnected snowmobile trails was a Bombardier original. It took a long time to get underway, but the past, present and future of the sport centers around trail systems. Ski-Doo engineers know this better than anyone else in the industry.

One problem with this concept is that what makes a great touring sled doesn't always make a good off-trail sled. Enter compromise. Enter rider inputs. Enter changes in the Mach I for 1991.

Before we talk about the new 617cc Rotax twin, think about what a performance sled has to do. It has to accelerate quickly from zero. It has to accelerate quickly from 30 mph to 60 mph. It has to reach a respectable top end, which in terms of the 1990s is about 100 mph. Expect the Mach I to fill the bill.

The new "long stroke" Rotax is a misnomer. It was raced in Formula III last season as a long stroke 580. Discard the euphemism and you have a 617cc twin with external RAVE exhaust which kicks in at between 6,000 and 6,200 rpm.

As you may recall, the Rotax Automatic Variable Exhaust (RAVE) system uses exhaust pressure to open a diaphragm in the external bell housing, which effectively increases the exhaust port size. This increases top end power. The idea of the RAVE is to help the rotary-valved twin develop strong low end and midrange performance while the exhaust port is at its minimum size and then opens at increased rpm to enlarge the port and increase power for top speed running.

The RAVE is standard issue on the new long stroke twin. The smaller 580 twin had a bore and stroke measuring 76mm by 64mm. The 617 twin retains the 76mm bore but gets a 4mm longer stroke that ups displacement by almost 40cc on the Rotax RAVE twin.

Performance is definitely enhanced across the power band of the 1991 Mach I. It isn't all the increased displacement. Jamming fuel into the larger engine are a pair of 40mm Mikuni slide type carburetors. Last year's 580 came with a pair of 38s. The new twin also gets two Mikuni fuel pumps. The thinking here is that designated individual pumps for each bigger bore carb maximizes fuel efficiency - especially at top end when you want the engine getting a maximum fuel load.

To improve carb breathing, the airbox has been totally redesigned for smoother air flow. Last year it was necessary to add a couple of holes to the stock airbox to increase air flow. The newly designed box eliminates that step.

We said this sled was sophisticated. Consider how Bombardier engineers got nearly three miles per hour more in top end by redesigning the clutches. Taking a trick from the track, Ski-Doo clutch specialists added windage plates - flat aluminum shields - to the primary clutch. This streamlining of the clutches reduced drag and improved speed. There is a trade-off. Covering the clutches reduces cooling. But modern day drive belts are much improved and should readily withstand the slight increase. Plus, the new Mach I has a totally new cowling with vastly improved ducting to direct cooling air under the hood. We've heard unofficially that this change could be worth as much as three horsepower at the jackshaft.

The new Type 643 engine also comes with a revised rotary intake valve with eight degrees longer duration so it can jam more fuel per cycle and ensure a smoother flow of fuel to the engine. To make the higher horsepower twin run more smoothly, Rotax engineers replaced the previous all metal balancer with a hydraulic damper. Mounted on the crankshaft and obscured by the recoil start, the hydraulic damper is used to cancel out harmonic vibrations. This damper consists of a steel weight floating in a reservoir of oil-based liquid. Measuring about a quarter inch in width and mounted by the flyweel, the unit is a new twist to reduce engine vibration.

The Type 643's crankcase is all new to better accommodate the longer stroke. But while much about the Type 643 is new, the design, based on the Type 583 (last year's 580cc twin), keeps the same basic head design and uses Nippondenso's 160 Watt electrics. Although the Nippondenso electrics are used on the liquid-cooled twins, Ski-Doo has switched to a new Ducati electrical system on the fan-cooled engines for 1991.

To reduce friction during the engine's initial break-in period, the new pistons are coated, allowing both tighter clearances and friction reduction. The coating is designed to wear off but it adds protection during the initial break-in period. Ski-Doo also upgraded the jackshaft to 4130 chromoly material for greater strength.

The clutch, with the windage plates, has been recalibrated to take advantage of the 10 percent increase in both power and torque. The Total Range Adjustable clutch is the best design to ever come out of Valcourt's shops. Like the Polaris and Comet clutches, the TRA system can be recalibrated to suit virtually any of the Formula or Safari models ranging from the 368cc fan-cooled twin on the Safari L all the way up to the Type 643 high performance liquid. There are six external easy-to-reach settings to adjust engine revs up or down depending on altitude, etc. Once the clutch is set, you needn't play with it. But if you have to, it's easy and can be accomplished by virtually any rider.

While the majority of riders will want to peer under the hood, it is the hood's design that sets this Formula apart from its forerunners. Ski-Doo spent a great deal of time and plenty of bucks getting this aerodynamic hood into shape at an Ontario research and design wind tunnel. If you recall, Ski-Doo's racing team developed previous twin-tracked racing configurations at just such a place. Not only was shape factored in, but size and location of hood louvers were developed too. The new styling gives you a large, central "NACA" duct under the halogen headlamp and dual intake louvers on either side of the cowling to direct cooling air to the muffler assembly and the clutches.

Powder riders will appreciate the new hood as the overall fit and finish has been improved. The improved sealing will keep powder from under the hood. There is even a collapsible front vent that can be sealed off if you ride in deep snow.

The Formula series offers a choice of high windshield or low blacked-out racing-style windshield. The taller windscreen is the best we've seen on a sports sled from Ski-Doo. It is high enough to divert wind over the rider, and wide enough to protect your hands from excessive wind.

Ride comfort is not limited to a new wind-deflecting hood and windshield. The rear monoshock suspension, which has up to 5.8 inches of travel, comes standard with a nitrogen pressurized Marzzochi shock. Although it is not a rebuildable type like Arctic uses on the EXT and Prowler Specials, the Ski-Doo shock offers similar advantages in rebound and compression damping.

The front progressive reaction system comes with 5.2 inches of suspension travel and new swaybar linkage that is freer floating. Since there will be no binding on the suspension support arms, the suspension should respond more smoothly on rough terrain.

A few other changes to the 1991 Mach I reflect added sophistication in this sports machine. To accommodate the battery necessary for the electric start option, the gas tank and seat were redesigned. The seat is narrower and fits flush with the aluminum chassis. The Mach's fuel tank, although restyled, still holds 10.8 gallons, plenty for an extended trail ride.

Another feature that shows that Bombardier's designers have been listening to Ski-Doo owners is the straighter handlebars. The "buckhorn" style, which not all Ski-Dooers liked, is gone. The new bar design gives you increased leverage and means that now you can use your shoulders instead of being forced to build up your forearms.

We had a lot of hands-on experience with Ski-Doos last winter - Safari and Formula models - and got used to the deep dish handlebars. For trail touring, it was fine. Once we became acclimated to them, we never gave it a thought one way or the other. But, given the choice, we prefer the new straighter bars. Ski-Doo's press release claims are true. You do tend to ride more relaxed and can feel more in control - especially if you want to do some "hot-dogging." While it is a bit of an overstatement to claim "...better handling and maneuverability," the bars do allow increased confidence and give you a more secure feeling, especially on tight twisty trails. We even found that rolling your throttle hand over when taking tight right handers was easier with the new bars. It is an improvement that you'll feel - then forget.

Like most top of the line sleds, Ski-Doo's Mach I gets a parking brake, full complement of gauges, carbide runners, and halogen headlamp. Unlike non-Bombardier sleds, the Mach gets a progressive, two-stage throttle. We really enjoy this set-up. Up to about half-throttle, your thumb enjoys a light and responsive pull. Beyond that, the throttle pull becomes "heavier" and much more deliberate. It's a quick way to make you realize that you've entered a new level of performance.

The new Mach I has a bigger sibling, the Mach I XTC with an extended track and two-up seating. There is a nifty combination backrest/storage rack. The XTC version uses the 138 inch long track versus the standard 121 inch rubber track. Both measure 16 inches in width.

One piece of luxury we didn't get a chance to test ride was the optional electric start. Fitting the electric start kit requires raising the Mach motor about an inch. If you are a diehard performance enthusiast you probably won't opt for the higher center of gravity, which may impact slightly on overall handling. If you are a go-fast touring rider, the convenience of key starting the long stroke Rotax will offset any minor change in handling. Personally, we'd opt for the electric start. When you are paying top dollar for a snowmobile, we think it's pretty silly to have to pull a rope to get it started. We like Bombardier's style, after all, would you buy a Porsche with a recoil starter?

Decked out in high gloss performance black with smart new script graphics, the 1991 Mach I is a Ski-Doo worthy of Canada's first snowmobile company. The new Mach is noticeably stronger at low end and midrange than the previous version. It has added definite "curb" appeal with the new styling. It's the first muscle sled to offer electric start. And you get the benefits of riding one of the snow world's premiere touring sleds.

The new Mach is a winner!