During the 1990s, motor enthusiasts were modifying 351 Cleveland 2V cylinder heads (by rerouting the coolant exit from the block surfaces to the intake manifold surfaces) for use in the 351W, resulting in the Clevor (combining Cleveland and Windsor). This modification required the use of custom pistons by reason of differing combustion chamber terrain (canted valves vs. straight valves) and intake manifolds. This combination yielded the horsepower potential of the 351C with the ruggedness of the 351W small block and was possible because more 351C 2V cylinder heads were manufactured than the corresponding engine blocks (the 351M and 400 used the same head as the 351C 2V).