While the Windsor 351 was in service, Ford was working on a more performance-oriented engine family, known by the internal code “335.” This would become the 351 Cleveland, named for where it was produced at Ford Engine Plant Number 2 in Cleveland. The 351 Cleveland (known as 351C) replaced the 351 Windsor (351W) in the Mustang for 1970. The big story for the Cleveland was breathing. The cylinder heads were basically Boss 302 units. Ports and valves were larger and the valves were canted. The 351 Cleveland two-barrel used 2.04-inch intake and 1.65-inch exhaust valves; the four-barrel version had 2.19/1.71-inch valves (except the ’73, which used the smaller valves). Ford kept the innovations going, offering no less than five different versions of the 351C in the 1970–73 Mustang.