wankel rotary engines

Inherent Obstacles
It was not my first experience with Wankel engines, I had tested some in early NSU cars in Europe and had been impressed with the turbine-smooth power delivery. At my first meeting with George Miller, the project manager, I was advised of a potential problem he hoped we could solve.

The Wankel exhaust runs very hot, and it would be important to make sure it did not become a problem in the sled installation. What did he mean by hot? Cherry red metal glowing under the hood, just like a coil on an electric stove. This was obviously much hotter than a two stroke muffler, and could be a serious problem. At that time the engines were mounted on top of the tunnel where the gas tank now sits on modern snowmobiles, and the gas tanks were in the nose. The muffler compartment was where the engines are now located; between the cross member and the tunnel. This meant that the cherry red Wankel muffler would be located only five inches away from a plastic gas tank. It was too late to redesign the engine location; it was to be mounted in the large luxury chassis which also housed the quiet machine.

This would turn out to be a plus. In order to control noise emission, this design had a completely closed hood with managed air circulation. This meant no louvers to let the noise out, and the hood tightly sealed to the pan. The problem with the hot muffler was solved only by allowing the air out after it had circulated around the muffler under several carefully-designed radiation shields. After the air had run through the fins to cool the engine, it was ducted over and around the muffler and finally out through a slot at the bottom of the muffler compartment right in front of the track.

The only reported problem with this design was a tendency to melt snow and ice under the sled if you let it idle too long before you shut it off. Occasionally owners would come out after a dinner at their favorite restaurant and find the track frozen to the ground, as the melted snow turned to ice. As far as I know, there was no problem with the close proximity of the gas tank to this glowing hot muffler, because the gas tank compartment had also been well insulated.

The Wankel concept had been criticized for its long sealing surface, and the complicated sealing strip arrangement around the rotor. The OMC Wankel engine had no such problems. The steel seal ran against metal-sprayed side plates and had excellent wear properties. One major problem occurred on the first production batch. The rotor bearings weren't to spec and some failures occurred until new bearings could be delivered.

OMC's Wankel-powered snowmobile lived up to its expectations as a test bed for the new engine concept. The Wankels were both smooth and relatively quiet for their time, and the power curve was a lot broader with lots of torque from a low engine speed. This made it completely insensitive to clutching. You could throw a bad clutch on this motor, and you would not notice it because of the exceptional four stroke-like delivery. Fuel consumption was also better than a comparable two stroke engine, but not as good as a conventional four stroke. This eventually became the downfall of the Wankel design. We were now in the early seventies, and then we got hit by the oil embargo. Fuel economy all of a sudden became a big issue, and the large automotive companies dropped the Wankel like a hot potato. OMC had hoped the publicity of the major car companies would create a favorable acceptance of the rotary engine, but now the exact opposite occurred. With all the bad publicity about the uncompetitive fuel consumption, OMC backed off its Wankel research.

OMC got out of the snowmobile business in 1975. The Wankel design team was disbanded, and most of the team members left for jobs at other companies. Only the Japanese Mazda company continued to make Wankel-powered cars, better known as the RX-7 Rotary, a very quick sportscar which gained an enthusiastic following.

If the Wankel concept had been allowed to continue on a limited budget, it may have emerged as a possible solution to the fuel consumption and emissions problems the sled and marine industries face today with two stroke engines. OMC built several large four-rotor outboards that were the most powerful outboards ever made, and when used in hydroplane racing, they totally dominated the competition. There is no doubt a very powerful compact rotary engine can be built, they are now very popular as power sources in sportscar racing in SCCA.

Future Uses?

Will we see rotary engines again in a snowmobile? It may depend on how strict the emissions rules become, and how much it will cost to tool up for new two or four stroke engines to meet these goals. The Wankel rotary engine had many good features that should have made it an excellent power source. Costs would have come down with continued development and reliability would have been engineered in. The design did not fail on its own merit, but was forced aside by circumstances. The expertise is still out there with the Mazda engines, and it would be a lot easier to get back into it now than it was to start from the beginning of the Wankel era.

As it turned out, the OMC snowmobile rotary engine ended up being the only Wankel engine ever manufactured in the U.S., and as such has some historical merit. There are still OMC rotaries out there in running condition to be had for a reasonable sum if you are interested in finding out what it felt like to run with rotary power.