After seeing a bunch of these mighty 4-bangers at Laguna Seca a few months back, we have to agree with commenter Discontinuity that the Offenhauser definitely belongs in this series. Based on a Miller marine engine, the first Offenhauser engine was built in 1933. For the next few decades, the twin-cam/4-valve Offenhauser utterly dominated the Indy 500, and it was still a strong racing competitor well into the 1970s. We're just disappointed that no Detroit automaker ever saw fit to offer an Offy Option on any of their cars. [Wikipedia]