Dyno Test: 2006 Polaris FST Switchback

New 4-stroke turbo cranks out 140 horses
RELATED TOPICS: SNOWMOBILES | POLARIS | ENGINES
If every dyno test only confirmed our prior assumptions, they'd become boring.

But when we finally got the chance to put the new Polaris Liberty 750cc twin 4-stroke turbo (FST) on the dyno, well, we were almost shocked at the power that our official dyno tester - Rich Daly at Dynoport - coaxed from this watercraft-based motor.

Riding prototypes last spring we'd thought it was horsy and was free of turbo lag, so waiting for the results was kind of like buying yourself a present and waiting to open it. We were a little giddy to see if it was really as peppy as we remembered it - in our test it hit 140.2 horsepower at 8000 rpm.
Three options
For 2006, the FST engine came in the FST Classic, FST Switchback and FST Touring packages. It delivered fairly smooth power in all with almost undistinguishable turbo lag. All the sleds were on the IQ chassis, but the Classic was a 128-inch tracked touring model with a FAST M-10 rear suspension, the Switchback was a 144-inch tracked crossover model with all the mountain ergos and the FST Touring was the 2-up Cadillac of Polaris' lineup. All had electric start and plenty of wind protection and we noticed our bigger test riders gravitating toward these sleds over others in Polaris' stable.

The numbers

Early last year Polaris told AmSnow that the new FST would be a 135-hp machine, so imagine our surprise when our machine topped out at 140.2 hp! Now we're told to expect a bit more power in the 2007 models.

Compared to non-turbo 4-strokes on the market, like Yamaha's Genesis 120 and 150 engines, the Liberty twin topped out at a little lower rpm - giving us full power at 8000 rpm. This peak power rpm reading was spot on with what Polaris told us before the season.

By way of comparison, Yamaha's Genesis 120 that we tested in Dec. 2004 showed us 118.8 hp at 8600 rpm and the new Genesis 150 - in the Apex we tested in Nov. 2005 - gave us 149.8 hp at 10,100 rpm.

Like other 4-strokes, the Polaris has a long, flat powerband with torque holding steady around 100 foot-pounds until reaching the higher rpm ranges. Foot-pounds only fell off to about 92 at peak horsepower. Compare that to the Genesis 150 engine that held steady around 80 ft.-lbs. and fell only slightly to about 78 at peak horsepower.

To be fair, the Polaris is working with a turbo so we aren't totally comparing apples to apples, but it's important to look at the similarities and differences across the 4-stroke gambit. Unfortunately, we didn't have an Arctic Cat T660 Turbo to test alongside Polaris' FST.

You'll see in this issue of AmSnow (p. 23), that Cat is stepping up its involvement in the 4-stroke arena too. Cat has added a rejunvenated Jaguar line of non-turbo sleds to its T660 and naturally aspirated lines. At press time, we didn't have dyno numbers on this machine, but you'll see them in an upcoming issue.

Bottom line

Polaris' FST is a more powerful engine than we originally thought. The fuel-injected powerplant with 15 pounds of turbo boost pulls smoothly, carries torque well throughout the powerband and easily meets EPA emissions compliance through 2012.

From early rides, the FST's engine outclasses the only other stock turbo 4-stroke, Cat's T660 Turbo. Yet, the T660 has become a reliable engine, while the FST has had growing pains this season. Our test sled spent its fair share of time in the shop. For instance, we followed a Polaris service bulletin to replace a starter gear and support bushing at the beginning of the season, and we also had starting and turbo problems that sent it back to the shop.

Final thoughts on FST?

It's powerful, has predictable turbo engagement and that quiet sound of the turbo spooling can give you some cool goose bumps!

FST test sled provided by Bibben's Sales and Service, Weed Sport, N.Y., 315-834-6500.
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