Review: 2008 Ski-Doo TNT

BRP Builds a Break-Through Sled

Jun. 21, 2007 By Jerry Bassett

Ski-Doo’s all-new MX Z TNT may be one of those breakthrough snowmobiles that we’ll look back on and mark as an industry highpoint, much as we do the original 1959 Ski-Doo or the 1967 Arctic Cat Panther with slide rail suspension or the 1980 Polaris TX-L Indy with the first independent suspension on a production sled. The TNT may mark the point where liquid-cooled, lightweight and the return to priced right fun re-entered our sport.

Is this Ski-Doo worthy? Check out these facts: liquid-cooled, performance-oriented 597cc Rotax twin; all-new REV-XP chassis; roomy, rider-forward cockpit; and, all this in a package that weighs less than 400 pounds! That’s the big news. A liquid-cooled, full-sized sports sled that comes in weighing less than a fan-cooled one at an entry-level price.

In the interest of full disclosure, this writer owns a fan-cooled 2006 Ski-Doo MXZ 550x. He owns it because he believes in lightweight handling above heavyweight power. But, the all-new TNT— heck the entire REV-XP line up for that matter— is making him rethink that position. The TNT is like riding a better handling 550x but with less weight and more power! And this writer likes his fan-cooled Ski-Doo— a whole lot! That’s what makes the TNT so impressive. It is incredibly likeable!

First Test Ride

When we were invited to Colorado to test ride the 2008 sleds this past March, we got excited. We had to know for ourselves just how good this new line of Ski-Doo snowmobiles could be. We had read a lot about the new REV-XP chassis and how Ski-Doo had expanded the riding position and taken a ton of weight out of its new line.

When we got to Colorado, we reserved the TNT for a late afternoon gambol on the trails outside Grand Lake. Frankly, we didn’t know what to expect. We figured the TNT with its 600cc Rotax—officially known as the 500SS engine—would have more gumption than a fan-cooled MXZ 550X, but we were very curious as to how it would handle.

All questions were answered in less than an hour as we discovered that those mountainous Grand Lake trails weren’t nearly as long as we thought. Slogging about all day with photographers and editors stopping to get the “perfect” shot tends to disrupt any ride and make a short trail seem miles longer. This late afternoon ride was solo. Perhaps a stupid thing to do considering the dangers that 11,000 feet of altitude can impose on a Minnesota flatlander, but one that we did anyway. No one with us. No one else on the trails. Alone. A 2008 Ski-Doo TNT prototype under us and the freedom to ride any damn way we pleased.

It was late in the afternoon, when the other magazine crews had returned from the day’s shoot and testing. We left the compound at a modest pace. We flexed the brake lever to make sure it worked correctly. A slam of the throttle to the bar for a brief test to check for free play. A bit of moving forward and back then side-to-side on the saddle to check the stickiness of the TNT seat covering. A bit of seesawing of the handlebars to check for ski bite and responsiveness. And then we headed up the main trail and away from view. Throttle full to the bar. The Rotax engine, deprived by altitude of about 30 percent of its sea-level potential, engaged the drive smartly and we were off.

The Power

The 500SS engine is a staple of the “budget” sports and touring sleds in the Ski-Doo line. This so-called “500” actually measures 597cc in displacement with a bore and stroke of 76mm by 65.8mm. A precursor to the 600 SDI, it is made affordable by use of twin 40mm Mikuni carbs and a lack of sophisticated semi-direct injection. Reed valves maximize fuel efficiency and there’s even a power-boosting Rotax exhaust valve system to broaden low-end torque and spike high-end performance. The 500SS twin is a solid 100-plus horsepower design versus the 600 SDI twin’s120-horsepower potential.

 

The lightweight TNT features rebuildable shocks and updated suspensions front and rear to make this sports sled a great value.

While the engine response is off by comparison to the SDI, it’s very good, even at Grand Lake’s power-robbing altitude. We did notice that when we ran full throttle into a tight turn and got caught up in the loose snow that had been tossed to the outside by a day’s worth of magazine test riders, there was a split second delay to getting back on the power. This is something you wouldn’t find with an SDI-equipped Ski-Doo. The compromise of carb jets will be noticeable versus an injected setup, even at sea level. But the TNT will be much happier away from the mountains.

Lightness of Being

What really caught our attention was how wonderfully light the sled felt. After a few turns, we really got into the TNT. It is easier to flick into a turn than Yamaha’s Phazer, plus the Ski-Doo has more performance to power you. It is hard to describe the TNT’s handling.

If you are a vintage sled rider, you know how light those sleds feel on the trail. Go with that and add power and equivalent handling.

Ski-Doo designers don’t play “safe” with the REV-XP styling. It is noticeably different than the first REV models.

The TNT is a great playmate. On one run we tried to be smooth. Clean entrance and exits through the turns. But, that was a bit boring. We found that the most fun was screaming down a straightway, busting the back end loose and seesawing the steering back and forth under power to slip around the tight turns. The TNT was as predictable as the old Polaris Indys—point it, do something ridiculous and let the sled sort it out while you laughed your way around the corner. The TNT turns even the AARP crowd into teenagers. And we loved it.

TNT vs Phazer

We notice that Ski-Doo has had to back off on its originally planned pricing and made the TNT a few hundred dollars more than the Yamaha Phazer. That’s $7,649.00 (US/MSRP) for the Ski-Doo versus $7,399.00 (US/MSRP) for the Phazer GT. Both are liquid-cooled and designed to encourage both new and budget-minded buyers to the sport.

The Yamaha 4stroke features a 500cc twin that ramps up to about 12,000 rpm. To get those speeds under control for the continuously variable drive system requires a somewhat complex gear reduction system. The Rotax engine easily revs to eight grand and delivers 20 more horsepower without added mechanisms.

While the Yamaha may look lighter than the TNT, the scales tell a very different story. According to Yamaha estimates, the Phazer GT weighs in at 491 pounds dry. Ski-Doo’s TNT comes in just under 400 pounds at 399! That’s Ski-Doo’s story with the TNT—lightweight, low cost, high fun quotient!

How They Did It

How did they do it? About the time the original REV series of sleds was launched, Ski-Doo engineers began working on the next generation REV that was even lighter and more rider-friendly.

They recognized that not all riders—especially taller riders—would like the limited movement and cramped leg room of the original REV. Moving the seat height up added extra riding area.

Racing-inspired seat offers more rider-friendly room for maneuvering around or flying over moguls. It’s also quite comfortable for enjoying a daylong trail ride.

Of course, it wasn’t just a case of moving the seat higher. The secondary clutch was relocated from alongside the tunnel to above the tunnel. That allowed engineers to reposition the rider, giving him an extra eight inches of legroom and more isolation from bumps.

All of this is why we could get real aggressive in cornering the TNT. We could move way forward, hang out for cornering and more easily break the track loose as we slid into the turns.

The change also eliminates that annoying knee slap on the cowl common to the previous REV sleds.

Because Ski-Doo had success with the original REV, engineers realized that they had a dilemma. They could make small changes in the REV like Polaris did with its Indy over the years, finally outdating itself and falling behind the competition. Or, they could take a riskier tack and essentially reinvent the REV. That was what they did, and it appears to have paid off handsomely.

They needed to keep the REV concept intact while totally reinventing it. The concepts of driver-forward position, centralizing the mass, use of the pyramidal frame design, and A-arm front suspension were retained. Virtually everything else was up for grabs.

Light But Strong

 

At its price point, the TNT offers much for many riders, and proves that you can build a liquid-cooled sled that weighs less than 400 pounds!

Weight targets were lowered, but durability targets were actually raised! Engineers studied everything and looked to shave ounces everywhere. They determined just how much wall thickness in tubing was necessary to meet strength parameters. They sought out new ways to combine functions and reduce total parts. They took 13 pounds out of the chassis, another seven out of the front suspension, eight from the rear suspension, eight each from the driveline and body. The result was the TNT at 399 pounds dry weight!

For the first time ever, Ski-Doo engineers attached data acquisition sensors to virtually every part of a prototype REV-XP chassis. By studying the results, engineers knew where they needed brawn and where they didn’t.

The resulting REV-XP chassis is said to be 17 percent lighter than the REV, but 21 percent stronger in torsion. Weight and parts were removed from the REV-XP’s steering assembly and resulted in a system that offers a 35 percent weight savings and a tighter turning radius.

The new drive shaft is a hydro-formed design (a technique used in building modern pickup truck frames) that results in the shaft being a large diameter ribbed hollow tube. Net weight savings was 41 percent versus the old REV. Strength and reliability showed gains using the hydroforming process.

Snowmobilers can appreciate the “hows” of getting lightweight, but they care more about on trail performance. And that means suspension. Ski-Doo redesigned the front and rear units. The REV-XP front end is lighter due to use of forged aluminum ski legs and some changes that came about with the new simplified design of the steering assembly.

Suspension Changes

The SC-5 rear suspension is a more refined version of the SC-4 with improved weight transfer and better absorption of bumps. Changes to the linkage of the center shock makes the action more efficient during its stroke.

Engine options for the REV-XP models remain the same, with more use of the 800R twin and retention of stalwart designs like the 600SDI and the TNT’s 500SS twin. What has changed is how the engines fit in place. The 2008 engine placement suspends the engines lower in the chassis for greater centralized positioning.

The driveline was repositioned and set above the tunnel to accommodate the rider position. This required a new magnesium chaincase design and use of the hydroformed driveshaft. Overall, there is close to a nine-pound reduction in this area.

Yes, it’s diminutive but proved to be more effective than it appears. Of course, there are wider and taller options to disperse more wind-chilling cold around you.

We can go on and on as to how many ounces Ski-Doo shaved here and there, but the bottom line is that this new Ski-Doo TNT is a low cost, lightweight marvel that takes us all back to a more fun time of snowmobiling.Despite its relatively low buck pricing, the TNT comes with take apart shocks, a raised handlebar for good leverage, and some very aggressive styling. Ski-Doo engineers incorporate this “in your face” stealth design to draw attention to the new sled, but it also incorporates effective wind flow to divert cold.

We Liked It

We were excited to try the new TNT back in March and we are excited now to tell you about it. These new REV-XP chassis models are the real deal. The TNT is a blast to ride, easy to handle and should be a real trail gem in the flatlands and normal sea level altitudes. If you want more, move up to the MXZ 600 SDI. However, you don’t have to. The TNT will be more than enough for most of us. Now try to find one.

-jb

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