The 351C, introduced in 1969 for 1970 model year, is commonly referred to as the 351 Cleveland after the Brookpark, Ohio, Cleveland Engine plant in which most of these engines were manufactured. This plant complex included a gray iron foundry (casting plant), a stamping plant, and an engine assembly plant. As newer automobile engines began incorporating aluminum blocks, Ford closed the casting plant in May 2012.
Production of the 351 Windsor V8 engine began for the 1970 model year in the Windsor Engine Plant #1. Ford sales and marketing forecast that the demand for this engine would exceed the plant's production capability, and it was decided the additional production would begin at the Cleveland engine plant. At this time, it was also decided to upgrade the engine to a higher-specification power plant. Two cylinder-head designs were developed to improve the 351W head. One cylinder head used the same basic design as the 351W, but with larger ports and valves; the other had canted intake and exhaust valves, similar to the Ford 385 Series V8. Sales, marketing, and product planning favored the canted valve design, as it was viewed as more innovative.
Other changes to the engine were related to ease of manufacture and improved reliability. This led to elimination of coolant flowing through the intake manifold to prevent unnecessary heat transfer. To perform this change, the front of the engine block was extended to include provisions for the coolant to flow through a cross over in the block. This extension also acted as an integrated timing chain housing. The timing chain housing was covered with flat steel that was easier to seal than the typical large timing chain cover used on other Ford V8s. These changes resulted in a bigger and heavier engine block than the Windsor V8s. The 351 Cleveland was not an all-new design, but a development of the 351W into a higher-performance variation.
The 351 Cleveland was introduced in 1969 for the 1970 model year. Its actual displacement was 351.9 cubic inches. A 4V performance version and a 2V version were built. The 351C-4V was marketed as a high-performance engine, featuring large valves and ports and a closed "quench" combustion chamber. Later versions of the 351C with 4V heads continued to use the large ports and valves, but switched to open chamber heads in an effort to reduce engine emissions. The 351C-2V was not marketed as a high-performance engine. It used the 2V cylinder heads with smaller valves, smaller ports, and open combustion chambers to produce a more economical engine that produced greater low-rpm torque. Only the Q-code 351 "Cobra Jet" (1971–1974), R-code "Boss" 351 (1971), and R-code 351 "HO" (1972) versions have four-bolt main bearing caps.