All the EJ series share compatibility and construction similarity and are 16 valved engines. The EJ series started with the EJ15, a single overhead cam (SOHC) and makes ~, then the EJ16, a single overhead cam (SOHC). Later followed by the EJ20, a single overhead cam and the EJ22, a single overhead cam. The EJ20 turbocharged version was developed with dual overhead cams, as well as non-turbo DOHC engines and DOHC twin-turbos. The EJ18 and EJ20 were most popular in Europe.