F500 Engines
Formula 500 cars are powered by a two-cylinder, water-cooled two-stroke engine. Modern cars use either the Rotax 494, or Rotax 493 originally produced for Ski-Doo snowmobiles. Older cars, mostly used for Solo events these days use the Kawasaki 440/A engine. The AMW 500L-85/250-2 R2c engine, while legal for use in Formula 500 racing, is rarely used these days.
The Kawasaki 440/A engine, produced by Kawasaki Heavy Industries, is a 436 cc piston port engine utilizing 38 mm Mikuni VM series carburetors and a tuned dual exhaust. While this engine is no longer competitive in road racing, it is still widely used in Solo II and Autocross events. Like all F500 engines, except for the AMW, the Kawasaki was originally produced as a snowmobile engine. It has been out of production since the early 1980s. Parts for these engines are becoming more difficult to find.
The AMW 500L-85 engine, built by Two Stroke International was introduced to F500 in 1994. It is a 497 cc reed valve engine using twin 38 mm Mikuni SuperBN carburetors. To keep the performance of these larger, more powerful engines in line with prior engines, SCCA mandates the use of a spec Y exhaust manifold and single tuned pipe on the AMW engine. Unlike the other engines used in F500, the AMW engine is a derivative of a light aircraft engine. This engine is no longer in production, and is not supported by the manufacturer.
Introduced for the 1997 season was the Rotax 494 engine. Rotax builds racing and industrial engines for a wide variety of applications, including aircraft, motorcycles, go-karts, snowmobiles and watercraft, The 494 cc Rotax engine is a rotary-valve engine. Like the AMW, the Rotax utilizes a 2 into 1 "Y" exhaust manifold and a single tuned expansion chamber exhaust. The Rotax engine utilizes the same 38 mm Mikuni VM carburetors as the Kawasaki. The Rotax engine has become, by far, the most popular engine in F500 road racing. Though the Rotax 494 is now out of production, Rotax continues to support it and provide parts.
In 2004 SCCA added the Rotax 493 to the list of approved engines. The 493, unlike the 494, is a reed valve engine. It also runs Mikuni VM series carbs and the "Y" exhaust manifold like its cousin the 494. Cars running the 493 engine are required to run at a higher minimum weight to maintain parity with the older 494 and AMW engines.
In 2011 SCCA added the Rotax 593 to the list of approved engines. The 593, (more commonly known as the Ski-Doo 500ss) is a 600cc version of the reed valve 493 engine. It also runs Mikuni VM series carbs and the "Y" exhaust manifold like the other Rotax engines, but are required to run a specified intake restrictor to keep power output on par with the 500cc 493 engine. Cars running the 593 engine are also required to run at a higher minimum weight to maintain parity with the older 494 and AMW engines.
Engine specifications are tightly regulated by the SCCA. No engine modifications are permitted in formula 500. Engines must be run in stock form "as delivered" from the factory. No aftermarket parts, port modifications, or other variations from stock configuration are allowed. This helps keep costs down and means close competition on the track.
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