Most Technologically Advanced Two-Stroke Engine

BRP's Rotax 600 H.O. E-TEC Engine
Ski-Doo’s E-TEC direct fuel injection technology is perhaps the biggest snowmobile product news for 2009. This technology makes a two-stroke engine burn so cleanly that its emissions ratings are cleaner than some four-strokes, according to Ski-Doo. We don’t doubt those claims.

Pull the rope on a Rotax 600 H.O. E-TEC engine (it takes just one, short-and-quick yank to light it) and there’s no smoke or smell at idle, just a steady, low rumble at precisely 1,200 rpm. Squeeze the throttle to engage the clutches and the sled glides away without a puff of exhaust smoke. Ride one all day and your coat will smell fresh when you return to the cabin or truck.

2009 MX Z X 600 H.O. E-TEC
The only mechanical difference between the 600 H.O. SDI and the E-TEC powerplant is the cylinder head, and that makes the 120 hp engine’s performance virtually identical to a semi-direct injected (SDI) 600 H.O. engine. Power comes on smoothly but quick torque snaps the sled out of corners. The pull seems stronger, though, on the pipe; when the vehicle is at higher speeds and engine rpm. This could be because the air/fuel ratio is right on the mark so it can make more power, whereas a semi-direct system isn’t as precise.

With the E-TEC system, fuel is delivered to the engine through injectors that are positioned next to each spark plug. Inside each injector is a wire-wrapped cylinder, a spring-loaded plunger and a spring-loaded piston.

2009 GSX LTD 600 H.O. E-TEC
Upon demand, the wire is charged with an electrical current that creates a magnetic force to push down the piston. This pressurizes the fuel, opens the plunger and shoots gasoline into the combustion chamber at more than 500 psi. The fuel must be highly pressurized because the engine piston simultaneously compresses.

Two charges make the system more precise, help reduce fuel consumption and reduce emissions. The stratified charge is in effect at low rpm and it burns the fuel before it can escape through the exhaust port. When engine speed picks up, the homogeneous charge takes over. The fuel mixes with air in the combustion chamber, is lit by the spark plug and then blown out the exhaust port.

2009 Summit X 600 H.O.E-TEC 154
E-TEC is cleaner and more efficient than carbureted and semi-direct engines that use ports to transfer fuel to the combustion chamber. With E-TEC, fuel vapor doesn’t have an opportunity to collect on the crankshaft or cylinder transfer ports because it’s directly injected into the combustion chamber.

E-TEC engines have transfer ports, but they’re used to move only air, not gasoline. The 600 H.O. E-TEC is available in MX Z, Summit, GSX and GTX models. All are based on the REV-XP body.

1200cc Rotax 4-TEC Engine
A Four-Stroke? From Ski-Doo?!

Ski-Doo has said in advertisements over the past few seasons that four-strokes are complex, heavy and they don’t necessarily offer benefits over an efficient two-stroke engine. Throw the new efficient, clean E-TEC into the equation and Ski-Doo could have launched a full assault against the four-stroke establishment.

But rather than continue to ignore an important segment of the market, the company released a four-stroke snowmobile for 2009 to reach what it says is a growing segment of snowmobile buyers. (Coincidentally, Polaris officials say four-stroke sales leveled off industry-wide last year.) The 1200cc Rotax 4-TEC is billed as a high-performance engine. The fuel-injected triple relies on one 52mm Mikuni throttle body.

2009 MX Z TNT 1200 4-TEC
We spent hours at Rode Reports on each, an MX Z 1200 TNT and GTX 1200. Power delivery just above clutch engagement was similar to a turbo-boosted engine where turbo lag adds a split-second for it to hit. Once the rpm builds and the vehicle reaches about 20 mph, the 130 hp engine feels lively.

2009 GTX SE 1200 4-TEC
Crack the throttle when coming out of a corner at about 40 mph and the claimed 500-pound MX Z 1200 feels stronger than a 600 two-stroke. Two more throttle bodies would make low-end power delivery more meaty and linear.

This seems too obvious of an upgrade for Ski-Doo to ignore, so maybe we’ll see an “H.O.” version of this engine with multiple throttle bodies within a year or two.

Engine braking slowed the prototype sleds when letting off for a corner. Ski-Doo engineers were still tuning the anti-engine braking system, but we expect a set of brake pads will last for the life of the machine even after the system is dialed in.

Ski-Doo engineers said they worked hard to develop a high-performance sound from the exhaust, which is a traditional layout with the muffler tucked behind the right side panel. The Rotax’s exhaust note doesn’t make us thank the Lord for our ears like Yamaha’s rear-exit system does, but it’s not as industrial as Polaris and Arctic Cat’s four-strokes. The 1200 4-TEC is available in MX Z, MX Z Renegade, GSX and GTX models. All are based on the new REV-XR body.

Low-Slung XR Body

The new 4-TEC four-stroke engine is too large for the XP body, so Ski-Doo developed the XR platform to house all models with the four-stroke engine.


Suspensions and the chassis are the same as XP-based machines, but new styling with wider side panels and new engine cradle provide space for the three-cylinder powerplant. The new body sports a bit more class with glossy side panels and low-slung, muscular style.

On-trail impressions varied across our staff. One test rider said XR-based sleds are surprisingly agile and sporty. They’re effortless to drive down the trail and predictable over bumps and through turns. Another rider was disappointed with the “feel” of the sled because it wasn’t as nimble as he expected it to be.

Some XR-based models include technology new to the Ski-Doo lineup. To reduce noise on GTX models, SilenTrack is a raised band molded into the track. It runs the full circumference near each edge for the idler wheels to roll on, which prevents the wheels from “falling” into the grauser bars. This is especially important on models with quiet four-stroke engines like the GTX 1200s. The GTX SE also includes a heated seat for the driver and passenger.

Another exclusive feature on the SE (only available with the 1200 engine) is the SC-5 Air Control Suspension (ACS). This system lets the driver control spring preload with a handle bar-mounted switch. An on-board air compressor adjusts the preload in 20-pound increments to one of five settings.

Unlike some other remotely adjustable systems we’ve tested, clicking the ACS from setting 2 to 4, for example, provides a noticeable difference in rear suspension performance. It was especially handy when two people who were 50 pounds apart switched roles from driver to passenger. Or, if we got into a section of rolling G-bumps that caused it to bottom, we made an adjustment on the fly and realized the benefit in about five seconds. Slick.

Revised Rear Suspension

New geometry in the rear suspension makes the SC-5 skidframe work better than last year’s machines. Original REV-XPs – especially MX Zs – were harsh in chatter but crashed out on big bumps.

Some aftermarket shops tried to correct the problem through revised shock calibrations, but success was limited. Ski-Doo snocross race teams tried to fix the problem all season, but the fact that drivers had limited success – at best – on the track points to the fact that the trouble was in the suspension itself, not the shocks.

For 2009, a revised rear torque arm and scissors coupled with revalved shocks makes the suspension more progressive, meaning the new geometry lets the suspension start softer to absorb small bumps and give a comfortable ride at slow vehicle speeds but become more firm as it compresses to resist bottoming on big moguls.

As a whole, MX Z suspensions were more compliant and controllable through chop all the way through the big rollers. Most importantly, the machines were more comfortable at speeds that drivers travel most often; 40 to 60 mph.

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