What is the difference between Ford’s 351 Cleveland, Windsor and modified engines? – Jalopnik

The Gen-I and II Chevy small-block have been largely the same basic engine since 1955 (except you, 400, you made things weird), but Ford V8s don’t follow the same rules. Asking for a ‘Ford 351’ is like asking for ‘a beer’. You must indicate which type. Ford’s 351 Cleveland, 351 Windsor and 351 Modified share only a few features. Factory examples have cast iron heads and blocks (except for a few experimental aluminum Cleveland blocks), a 4-inch bore, 3.5-inch stroke, 4.38-inch center spacing, external balancing, and a firing order of 1-3-7-2-6-5-4-8. (Don’t expect the parts to be interchangeable, thankfully.)

The 351 Windsor grabbed the block from the 302, raised the deck height by a whopping 1.5 inches and marched off to compete with the Chevy 350s and Chrysler 340s. Ford used it from 1968 to 1997 in models such as Thunderbirds, E-Series vans, Mustang Mach 1s, the original F-150 Lightning, and the 1995 Mustang Cobra R. In 1970, Ford introduced the 335 series V8 engines, including the 1970-1974 351 Cleveland. The Cleveland is a performance engine with heads that flow more air than a filibuster politician, which is why it powered the Boss 351 Mustangs and De Tomaso Panteras. The 1975-1982 351M (the “Modified” designation was fan created, Ford never said “M” stood for anything), while still part of the 335 series, was in fact a discontinued 400. It only existed to cut costs as Ford eliminated the short deck Clevelands to make only high deck 335 series engines with different strokes.

Both Windsors and Clevelands have strong ductile iron cranks with a tensile strength of 95,000 psi and excellent fatigue resistance. Cast iron (tensile strength 80,000 psi) is slightly more brittle. While the Cleveland’s smaller main bearings may seem insufficient, the diameters of the crank journals don’t really contribute to overall strength and smaller main bearings generally translate into faster turning. It’s a bit like the situation with Chevy’s LS6 454 and Pontiac’s 455 Super Duty. Speaking of mains, 1971 Mustang Boss 351 Clevelands got a four-bolt mains, not to mention forged aluminum pistons and an aluminum intake (while regular Clevelands only got iron intakes).

There is no argument that Cleveland heads flow better than Windsor heads, which has helped establish Cleveland’s performance reputation. The canted valves and giant ports are wider than someone’s nostrils after eating a piece of fresh horseradish, especially in the four-cylinder heads with their 1.71-inch exhaust valves and 2.19-inch intake valves, the largest intake valves on any midsize V8. (There is also a Cleveland with two cylinders and smaller ports).

Ford’s 351M also uses unique high-dish pistons that lower compression to meet mid-1970s emissions regulations, which vary between 7.74:1 and 8.6:1 depending on the year. While the Cleveland and Windsor both use a “small-block” bell housing, the 351M and 400 use the “big-block” housing, not to mention the three engine mounts compared to the Cleveland’s two. Both the 351M and 400 were available in Ford cars through 1979, while trucks kept them in use until 1982. Confusingly, Ford sometimes referred to the 351M as a “Cleveland,” which is just kind of mean since it made some owners think their pickups came with 351 Clevelands.

Oh, and before we’re done: no, the 1969 and 1970 Mustang Boss 302 heads are not from the 351 Cleveland. Remember, 302s are Windsor engines, and they won’t take kindly to someone with a Hercules head blasting through them where there are no willing wires. The actual Boss 302 heads are actually Windsor heads modified to be as close to Cleveland’s as possible while retaining the same cooling passages and bolt pattern.