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Heinrich’s designs became very popular with new snowmobile manufacturers due to their reputation for both power and reliability. Kohler’s new line of engines included the fan-cooled AS 340cc and 440cc engines. Next came three Free Air engines: the FA 340 and 440 twins, and a 440 triple. As the program matured and demand grew, a series of liquid-cooled twin engines (LC 250, 340 and 440) was added to the lineup.
With the successes of Arctic Cat, Rupp, Mercury, and numerous other brands racing with Kohler engines, Heinrich got a chance to go for the “Ultimate 440” race engine design. At this time, max power on the motorcycle road racing circuit was achieved with a greater number of smaller cylinders revving at increasingly higher engine speeds. They raced 125cc twins, 250cc 4-cylinders and even a Moto Guzi 500cc V8 engine. Martin decided the “Ultimate 440” engine should have eight cylinders, but arranging that many cylinders, intakes and exhausts was certainly a challenge that had not yet seen a practical application in the motorcycle world.
Heinrich’s solution was to stack two opposed-firing 4-cylinder engines on top of each other, and gear them to a common center shaft rotating at half speed, thus creating an H-8 engine. This design may seem radical, but H engines were not uncommon in World War II aircraft, which had combinations of up to 24 cylinders. It was also in the BRM Formula 1 car engine, which had 16 cylinders. By using the H-8 design, Heinrich could place four rotary valves on each side and run four pipes out the top and four pipes out the bottom. With a 41.5mm bore and a 40mm stroke, the engine had a displacement of 433cc, and each cylinder was a moped-size 54cc.