What do the 10A, 12A, 13B & 20B Mazda engine designations mean?
The numbers represent metric displacement. Power is generated from one face of each rotor per shaft revolution. 10 is the result of two 491 cc rotor chambers, 982 cc total, which rounds to 1.0 liters. 12 is the result of two 573 cc rotor chambers, 1146 cc total, which incorrectly rounds to 1.2 liters. 13 is the result of two 654 cc rotor chambers, 1308 cc total, which rounds to 1.3 liters. 20 is the result of three 654 cc rotor chambers, 1962 cc total, which rounds to 2.0 liters. The letters “A” & “B” represent the combination of two basic production engine configuration parameters, “eccentricity” and “generating radius”. The “A” is applied to the first (A), and only, combination of the two specifications actually deployed in a regular production engine of nominal 0.60 liter displacement per rotor, the 12A. The “A” was also applied to the first (A), and not only, combination of the two specifications actually deployed in a regular production engine of nominal 0.65 liter displacement pe
