Briggs & Stratton has been producing high-quality engines for lawnmowers, snowblowers and custom racing since 1908 and is currently the largest producer of small gasoline engines in the world. Briggs & Stratton has offered 5 horsepower engines since the introduction of the Raptor, which was the primary engine in the company's racing line until it was removed from production in 1999 to comply with new environmental regulations. Briggs & Stratton continues the tradition of the Raptor 5 horsepower model with its Animal, 206 and Word Formula racing engines.
The Briggs & Stratton Raptor engine features a bore between 2.56125 and 2.5625 inches and a stroke of 2.438 inches. This corresponds to a total engine displacement of 12.48 cubic inches per engine cycle.
More modern Briggs & Stratton 5 horsepower engines feature the same 12.48 cubic inches of engine displacement, but achieve that volume of displacement using a wider bore and a shorter stroke. The currently produced Animal, 206 and World Formula engines feature a bore between 2.6875 and 2.6885 inches and a stroke of 2.2 inches.
The original Raptor series of engines featured a compression ratio -- the ratio of the length of the stroke to the length of the combustion chamber -- of 6.5 to 1. Despite their shorter strokes, modern Briggs & Stratton engines also feature shorter combustion chambers and thus have higher compression ratios. The World Formula has a compression ratio of 9.5 to 1, the 206 has a compression ratio of 9 to 1, and the Animal has a compression ratio of 8.5 to 1.
The factory-specified optimal ignition timing for the Raptor engine is 22 degrees before top of dead centre (BTDC). The Animal, 206 and World Formula engines are factory-designed for an ignition timing of 29 degrees BTDC.
Many users modify their Briggs & Stratton racing engines to improve on, or the stretch the limits of, engine performance. If you purchase a used Briggs & Stratton motor, ask the seller about any modifications that have been performed and how they may affect engine performance.