As Snow Goer celebrates the 50th anniversary of its founding, it has given editors a chance to page through each and every edition of the snowmobile magazine’s stories past. Occasionally this season, we’ll share articles that, for one reason or another, caught our eye during that research. The review of the 1976 Polaris TX 340 snowmobile was published in the September 1975 issue of Snow Goer, with opinions based on the magazine’s tests of pre-production models the previous spring.
Also a part of the Snow Goer 50th Anniversary celebration is the Get Up & Go Sweepstakes. Make sure to enter to earn a chance to win a 2017 Ski-Doo Renegade Adrenaline 850 E-TEC snowmobile, a two-place Triton trailer, power tools from Makita, a helmet from BRP, Dennis Kirk gift certificates and other great prizes. Click here for details.
Polaris TX 340
At last, a lightning-quick Polaris
Any sled that was designed by a Research and Development team consisting of international snowmobile racers Bob Eastman, Leroy Lindblad, Jim Bernat, Don Omdahl, and Professional Drivers Circuit champion Larry Rugland is certain to be racetrack quick and enduro tough. That’s exactly the case with the Polaris TX 340 that Snow Goer tested last spring.
Polaris perceives this new TX as a Jekyll and Hyde machine. The Mr. Hyde version, for the track, is to be sufficiently done out in gobs of horsepower capable of competing with various Twisters, Sonics, RVs and Z El Tigres. The more sedate Dr. Jekyll version, like the trail TX 340 supplied for Snow Goer’s spring test session, will be capable of traveling deep rutted trails with precision and of speed to make crossing frozen waters seem like a ride in a Don Garlits dragster. While we can’t even pretend to say how the racing TX will fare, Snow Goer can state that the trail version will satisfy just about anybody, especially those old TX owners who are ready for a trade.
And there’s good reason to trade. At 66 mph, through the quarter mile, the 340 TX tied last year’s 440xx TX that Snow Goer tested in similar Colorado mountain terrain. Only last year’s TX had a half mile to unwind. Times through the eighth and quarter mile acceleration runs of 12.3 and 19.7 seconds, respectively, compared favorably with the 440cc and 500cc engined sleds tested this year.
Taking full advantage of PDC port designs and cooling, the 335cc Star engine pumped out 22 delivered track horsepower on the portable Hartzell dyno. That was second to a 500cc sled that delivered 24 hp. Under no-load conditions, the TX hit 62 mph.
To get that performance, Polaris engineers have increased the engine’s breathing by incorporating the same transfer port design as used on the PDC engines. Both the fin design and use of larger cooling fins also follows PDC practice. Internally the 335cc Star engine consists of a 62mm chromium bore with a 55.6mm stroke.
Externally there are twin 34mm Mikuni slide valve carburetors, which use a flip choke lever instead of the push-pull type seen last season. Another change for ’76 is the two-into-one tuned exhaust. A departure from the twin expansion chambers used on the ’75 440 TX that Snow Goer tested last year. Packed with extra fiberglass, the new Polartone unit helped reduce engine noise to 74.2 decibels and still delivered outstanding performance for the 340 twin. The new design exhaust is said to give improved low rpm torque. While it is impossible to judge the improvement without simultaneously testing a ’75 TX 340, the engine response at all speeds was excellent on the test machine.
In conjuction with the redisgned exhaust is a new L-shaped intake silencer. Foam baffling with five rectangular breather inlets reduces the airflow noise. If you think that carburetor silencing is a small part of sound control, try removing your car’s air cleaner next time you drive around town. The baffle housing itself mates with the covered duct located behind the windshield. Other silencing includes rubber cushion mounts between the engine’s head fins and foam mounted in the cowling. With sound playing such an important role for ’76, the cowl has been shaped to virtually envelope the powerplant, leaving only a squared off frontal aperture for free air cooling. To further aid cooling the Snow Goer test sled had six rectangular holes mounted in the bumper which permits air to pass over the exhaust and crankcase. This will be changed in regular production versions where only four holes will be used. To augment cooling, a scoop has been mounted on the front air intake to direct incoming cool air directly downward to the crankcase and cylinder. While engine performance relates directly to throttle response, clutching also plays a critical role. Here the ’76 TX departs radically from previous Polaris high performance consumer sleds. There is still a heavy duty drive clutch, but the secondary clutch, instead of being mounted integrally with the chaincase, is placed on a cross shaft arrangement. The cross shaft affords a lower profile and center of gravity. Not totally satisfied Polaris engineers further reduced the cg by placing the clutch spring components in a bellshaped housing mounted outboard of the clutch. This system permits placing the entire shaft lower in the body.
As is typical of Polaris, the secondary clutch was born on the racetrack, and was first seen in the ’73 Starfire racers. Both Sno Pro and PDC racing sleds have used the design. Updated through the seasons, the TX clutch will be identical on both track and trail TX sleds. There will, however, be a change in primary clutches, with the stock racer having different ramps and weights designed to accommodate the more powerful track TX engine.
Total performance from the power package showed in acceleration of 12.3 seconds through the eighth mile and 19.7 seconds through the quarter mile runs. Combined with an already mentioned top speed of 66 mph, the Polaris TX becomes a formidable trail sled.
Another concept patterned after PDC racers is the brand new suspension. Made of extruded aluminum, the suspension trails offer lighter weight over the steel rails used in last year’s TX. Instead of a single spring controlling both front and rear suspension adjustments, the new TX has separate spring systems for greater ride adjustments. At the front torque arm there is a spring weight adjustment independent of the rear spring. To compensate for driver weight and terrain, there are three notches for rear spring adjustment. A single cente-pivoted tubular shock dampens the overall ride.