There are instances where OEM design is so good that it lends itself to a broad range of applications within the high-performance aftermarket. Some good examples are the Mustang II frontend, Corvair ...

Duvernay has the highest stock output production Quad 4: the 190-hp 1991 to 1992 RPO W41. The 1993 W41 lost 10 hp due to smaller exhaust ports. Photo: Kevin Davis via Wikipedia (CC-3.0) See All 9 ...