BY DAVID WELLS
When the revolutionary Polaris
Indy TX-L appeared for 1980, it was powered by a liquid-cooled 340 twin from the mid-1970s that had been built to compete in cross-country racing, which then had a 56-horsepower limit in force. By 1983, tooling for the 340-class race engine was worn out and the Indy liquid twin sorely needed major renewal throughout the chassis.
The result was the new Indy 400, a versatile trail sled that fit squarely between the porky and pricey Indy 600 three-cylinder lake racer and the family-oriented fan-cooled Indy Trail in both price and performance.
The two-cylinder configuration was significantly lighter than the triple and allowed much better handling in the twisties, while liquid cooling gave it a better top end than the Trail. It was also quieter and offered other advantages.
This new Indy liquid twin sled was more than just a facelift with a new engine. It included many refinements that attracted new buyers to Polaris and helped take the brand to the top of the sales charts as the decade of the 1980s unfolded.
In late 1984, a 300-unit pilot build of Indy 400s with the new engine and a new drive clutch installed in the ’ 84 chassis was sold to customers. Full production did not start until 1985 models, which had numerous changes.
The new, over-square 400 “water burner” had a mono-block construction like the 340 it replaced instead of separate jugs like the 600 triple and the 440 fan in the Trail. However, it had both a larger bore and a longer stroke than the 340, with smaller carbs fed by a new cool air intake behind the windshield.
The sled also got the huge convenience of oil injection plus a new easyto-bleed cooling system. The ’85 models received an improved exhaust system that was not on the pilot build’ 84 400s.
Offering six more horsepower, more torque throughout the powerband and better fuel economy than the old premix 340 race engine, this new, lower-revving 398cc engine was much better suited to trail riding. It even turned in an amazing 27.86 miles per gallon at the third annual Snow Goer Fuel Economy Test, the third best performance of nine sleds tested in a 100-mile conservatively-paced competition.
Another upgrade for the full-production Indy 400s was a third heat exchanger at the front of the tunnel. This provided too much cooling under some conditions, so 400s were retrofitted with a snap-on hood vent cover to deal with this issue.
The new Indy liquid twin also introduced the new P-85 lightweight, openbody drive clutch that offered better belt and clutch life with easier tuning and maintenance. It quickly became the only clutch for the entire Polaris lineup, was widely regarded as the best in the industry, and lasted as the standard star brand drive pulley for decades. Re-contoured skid frame rails and two more wheels improved hyfax life in marginal snow conditions on the 1985 models too.
Polaris was also now more engaged in major fit, finish, comfort and overall appearance upgrades on its sleds. The new 400 got a contoured seat with a sewn multipiece cover that was styled after the excellent seat on the Indy Trail. It featured a real butt pocket for much better comfort than the old flat and slippery Indy bench seat.
When the mechanical details were all finalized, the Indy 400 was also 16 pounds lighter than the Indy 340 that it replaced and only 13 pounds heavier than the less powerful Indy Trail.
Finally, the new Indy 400 was wrapped in a black finish with red and silver trim that made it the best looking sled in the entire 1985 Polaris model lineup, so it was thoroughly better than the old 340 in just about every way possible.
The new 1985 Indy 400 was one of the stars of the spring 1984 magazine test session. Snowmobile magazine found that the Indy 400 had “a whole new personality ” when compared to the old 340.
“Where the 340 required concentration always and maximum concentration if you wanted to ‘book,’ the 400 features a much less demanding feel,” they reported. Our Snow Goer predecessors loved it too. “The rougher it gets, the more twisting the trail, the better the Indy (400) likes it,” reported one Snow Goer editor. “The Indy simply allows you to drive much faster, under complete control than the leaf-spring rigid-front sleds.”
On a personal note, I had a 1986 Indy 400, essentially the same sled with different decals, and found it to be a thoroughly enjoyable trail machine, if a little underpowered for its weight. That would change in 1989 with the new Indy 500 liquid twin, but that’s a story for another time. Meanwhile, 1991 was the last year for the Indy 400 before it was punched out to a 440.