Friends ask me sometimes, "I've found
this really cool (insert sled name) free-air for (insert price). Should
I get it?" If you find yourself wondering this very question, or just want
to know something about free-air (F/A) sleds, this is the article for you.
Free-air cooling began in snowmobiles used for racing during the early
70's. Manufacturers realized that by casting bigger fins onto the heads
and cylinders of the engine, and then placing the engine in the airstream
moving by the sled, acceptable cooling could be accomplished. The cooling
was more even then with fan cooled engines, which tended to run hotter
on the cylinder farthest away from the fan, and weighed less than a fan
cooled setup. It also didn't waste horsepower turning the cooling fan (or
risk throwing the belt). Because of these advantages, the free-air design
survived until the late 70's, when liquid cooling finally took over.
Although the F/A setup does have adavantages, like everything else, it
has disadvantages as well. Free-air sleds are generally designed to stay
moving. In racing, where the design was first used, this is not a problem.
In fast trail riding (like on railroad beds), this is not a problem. But
if you're puttering around the yard, and it's a warmer day, sometimes you
can run into overheating problems, especially if you sled's tuning is off.
Of course, in what conditions this happens varies from sled to sled, but
it is something to be aware of. Free air sleds also tend to be slightly
more tempermental then their fan cooled cousins, mostly because of the
higher state of tune that the engines are in. All in all, free-airs are
best left to the more experienced vintage collector/rider. That's not to
say that if you happen to find a 75' F/A T'nT 245RV in perfect shape for
$50 and you are new to vintage snowmobiles you shouldn't get it, but on
that same note, perhaps it shouldn't be your first sled choice.
Phillips, Stib Inc.
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