The Ford 335 engine family were a group of small-block V8 engines built by the Ford Motor Company between 1970 and 1982. The series was nicknamed Cleveland after the Cleveland, Ohio engine plant in which most were cast.
- See also Ford Boss 351 engine
The 351 Cleveland was introduced in 1970 as Ford's new muscle car engine. It was built through the end of the 1974 model year. It incorporated elements learned on the Ford 385 engine series and on the Ford Boss 302 engine, particularly the poly-angle combustion chambers with canted valves and the thin-wall casting technology. Both a 4V (4-barrel carburetor) performance version and a 2V (2-barrel carburetor) basic version were built. The latter had a cylinder head with smaller valves to suit its intended applications. The 351 Cleveland was produced through the 1974 model year (although it remained in production considerably longer in Australia), when Ford decided to economize and use the same block for both 351 and 400 cubic inch (5.8 and 6.6 L) applications.
This engine was built only in Australia, and was intended to give their consumers a five liter alternative to the 351 Cleveland as the Ford "Windsor" series of engines was not commonly available there. Utilizing a locally produced 351 Cleveland block, 302 cubic inches (4.9 L) was attained by reducing the stroke of the 351C from 3.5 to 3 inches (89 to 76 mm). Additionally, the 302C cylinder heads were designed locally, with smaller combustion chamber to compensate for the reduced stroke of the engine. These heads interchange directly onto 351C engines, and are highly sought outside of Australia as a low-cost method to increase compression ratio.
The big-block FE engine family was getting rather tired and outdated, and the 385 family could not meet the efficiency requirements of the time. At the same time, the small-block Windsor engines were too small and high-revving for Ford's fullsize car and truck applications. So the company went to work on a new small-block to meet the desired levels of economy while still providing the kind of big-block torque that was needed to move 2+ ton vehicles.
The Ford 400 engine had "square" proportions, with a 4.0 in (102 mm) bore and stroke; it therefore displaced 402 in³ (6.6 L), making it the largest small-block V8 ever made. It was introduced in model year 1971 with a full half-inch (13 mm) longer stroke than the 351 Cleveland, making it the longest-stroke Ford pushrod V8 engine. A long-stroke engine has good low-end torque, for which it trades high-end power. This was a good compromise given Ford's requirement for an engine to power heavier mid-size and full-size cars and light trucks. The M-block, as it became known, was the last pushrod V8 block designed by Ford, and it had a deck height over an inch (25 mm) higher than the Cleveland.
The 400 was seen as a smaller and lighter replacement for the big Ford 385 engines, the 429 and 460, in Ford's big cars. It was originally available in Ford's Custom, Galaxie and LTD lines, and in Mercury's Monterey, Marquis, and Brougham. Later, it would power the Ford Thunderbird, the Lincoln Continental, and Mark V.
The 400 uses the same bellhousing bolt pattern as the 385 family big-block to make it compatible with the higher torque-capacity C6 transmission used on the large cars and trucks. The 400 was modified in 1975 to use unleaded gasoline.
When the 351 Cleveland was withdrawn after the end of the 1974 model year, Ford needed another engine in the 351 cubic inch (5.8 L) class, since production of the 351 Windsor was not sufficient and the 390 FE was being retired as well. To replace the 390, Ford took the 400 engine's tall-deck block and de-stroked it, with a shorter throw crankshaft and longer connecting rods, to produce a 351 cubic inch (5.8 L) engine whose components were largely compatible with the 400. This engine was called the 351M and as a back-formation the taller-deck block became known as the M-block. These engines were built in Cleveland, and the performance reputation of the 351 Cleveland engine was such that the company continued to refer to "351 Cleveland" in marketing for a couple years after the change.
Light truck usage
For the 1977 model year, Ford decided to replace its ageing FE big-block 360 and 390 engines in its light truck line with its new 351M and 400 engines. For light truck use, beefed-up blocks were designed. These enhancements were added to all M-block engines starting with the 1978 model year.
Replacement in cars
1979 was the final year the M-block engines were used in cars. After that, the Ford 351 Windsor at 5.8 L was the only large car engine used. Reduced demand for large engines due to fuel economy regulations led to the abandoment of the Cleveland production line that produced the 351M and 400 engines.
Replacement in trucks
The M-block engine was designed when first-generation pollution controls were already in place in the United States, and the engine was designed to support the Thermactor air injection reaction (AIR) and exhaust gas recirculation (EGR) systems internally inside the block and heads. Previous engine designs required bulky and unsightly external tubing to feed Thermactor air into the exhaust manifolds and exhaust gas to the EGR valve below the carburetor, but this was all built in to the M-block engine.
This all made adapting the M-block to the second generation of emissions control equipment harder. One requirement of the second-generation equipment was an O² sensor in the exhaust, which had to be placed before the Thermactor air was added. Since Thermactor air was injected right into the block's exhaust ports in the M-block, there was nowhere for the O² sensor to go.
It would have been possible to alter the M-block to work, but it would have required significant effort. Ford decided to simply scrap the M-block engines and replace them with updated 351 Windsor engines at the small end, and a combination of the 6.9 L Navistar diesel and the 460 at the top end. 1982 was the last year the M-block was sold.