The engine mounted in the Mazda 787B was the Mazda R26B four-rotor engine (RE). The original version of this engine was the 13B engine with a displacement of 654cc x 2 rotors, was developed in 1973 for the higher grades of the second-generation Luce. The 13B engine was later developed for the second-generation Cosmo, Luce Legato, Roadpacer, RX-7 and other models, and became the main power unit in the RE lineup. Going through several refinements, including 6-Port induction, a lean combustion system, and turbocharging, it continued to be made for about 40 years until the 13B MSP RENESIS engine was mounted in the RX-8, which was discontinued in 2012.
The 13B motorsports engine was first used in the Fuji GC series in the 1970s utilizing a peripheral port intake, and while it was small and compact, it boasted a high output of 300 PS and outstanding reliability, making it a favorite among many private racers. In Le Mans, it was first used in the RX-7 252i in 1979 and was used right up until the Mazda 737C in 1985. Later 3-rotor and 4-rotor engines utilized the same dimensions and shapes as components from the 13B, including the four rotor housings (which correspond to the engine block and cylinder head of a reciprocating engine) and each rotor (which correspond to pistons).
The first four-rotor engine, the 13J, was built in a short time, and its power output did not reach 600 PS in spite of the simple build-up. Furthermore, although being a lightweight and compact package was seen as the ultimate strengths of an RE, the 13J engine was long and heavy. Even so, within a few months, the front length of the engine was greatly reduced and a lighter, improved 13J engine was developed. However, the hasty development took its toll, and in 1988, the newly developed Mazda 767s with their four-rotor engines suffered many problems and fell far behind in the race, finishing a disappointing 17th and 19th overall.