Ford Small-Block Engine Parts Interchange. George Reid

arrived in mid-1969 with chrome stamped steel valvecovers, which continued into early 1970 before Ford replaced them with the finned cast-aluminum valvecover shown here.

       The Boss 302 was not available with ram-air in 1969. However, the ram-air shaker was available as an option for 1970.

       The all-new 351 Cleveland arrived in 1970 primarily in 4V form with the Autolite 4300 carburetor, though 2V versions were also produced when 351W-2V engines were in short supply. The 4V version was fitted with wedge chamber heads and large ports yielding 11.0:1 compression. The 351C-2V engine was an unplanned 11th-hour undertaking for Ford, arriving with open chambers and smaller intake and exhaust ports for improved low-end torque at 9.5:1 compression.

       This 1973 351C-2V is devoid of the ram-air feature with a Motorcraft 2150 carburetor. What the 351C-2V engine had going for it was better low-end torque than the 4V with larger ports. The 2V’s smaller ports offered better low-end street performance yet fell on its face at high RPM.

       The 351C with ram-air for 1973 was available only with 2-barrel carburetion thanks to tougher federal emissions standards.

       The 1971 Boss 351 and its lower-compression sibling, the 351C High Output for 1972, made the most of the Cleveland’s potential with a hot mechanical flat-tappet camshaft and screw-in, adjustable rocker arm studs. The 351C High Output was available for a short time in 1972 before Ford ended production mid-year.

      Because the 351C has at least two GM nuances to its architecture, block configuration and poly-angle-valve cylinder heads, it raises questions as to how this engine family was developed in the first place. This has been a point of speculation for many years. The 351C block looks like a Ford/Oldsmobile hybrid with 289/302/351W bore spacing and size coupled with an Oldsmobile V-8’s front-end architecture that includes abundant cast iron and a steel plate timing cover, 12/6 o’clock bolt-pattern fuel pump (the only Ford V-8 to have the 12/6-pattern fuel pump), and a cast-iron water pump that also resembles Oldsmobile’s. On top, the Cleveland’s poly-angle-valve cylinder heads with those large ports and wedge chambers closely resemble Chevrolet’s 396/402/427/454-ci big-block castings of the era.

       It is believed that Ford planned for one engine family, the 335-series Cleveland, to cover all engine sizes and to reduce costs. The raised-deck 400-ci Cleveland was introduced in 1971 to replace the 390- and 428-ci FE engines in full-size cars and trucks. In 1975, Ford dropped the 351C low-deck block and destroked the 400 to achieve the 351M. Ford never called the 400 “400M.” Only the 351M is considered the “M” (for Modified or Midland) engine, although it is called “400M” the world over. (Photo Courtesy Tim Meyer)

      The 351C is identical to the 351W in terms of bore spacing, size, and bolt patterns. However, the 351C block is a completely different casting designed to take on larger cylinder heads with poly-angle valves, huge wedge and bowl-shaped chambers, and smaller 14-mm spark plugs. The 351C is a higher-revving V-8 thanks to large ports and improved breathing. Also different from the 351W is the thermostat’s block location, instead of on the intake manifold as you find with the 289/302/351W.

      From the beginning, 2- and 4-barrel versions of the 351C were produced with 9.5:1 and 11.0:1 compression ratios, respectively. Compression was determined by combustion chamber size. The 2-barrel head has a large open chamber to reduce compression; the 4-barrel head has a wedge chamber. The downside to the 2-barrel head’s open chamber is pinging and detonation issues that make it undesirable. The upside is smaller intake and exhaust ports for improved low-end torque. The best Cleveland factory head comes from Australia with the 4V wedge chamber and 2-barrel intake and exhaust ports, making it the optimum cylinder head for this engine.

      The 351C-2V engine is more suited to street performance and low-end torque because it has smaller intake ports for improved velocity. The downside to the 2V cylinder head is large open chambers and poor quench, which makes it susceptible to detonation (pinging). I have never been particularly fond of the 351C-2V cylinder head; however, Tim Meyer of TMeyer Precision Automotive Machining tells me that the 351C-2V head is perfect for street performance if you watch compression and are not planning high-RPM/wide-open throttle operation, which is where detonation takes place.

400/351M

      Like the 351C, we will probably never know what led to the 400 Cleveland in 1971 and the 351M in 1975. The 400/351M was a raised-deck (1-inch taller) Cleveland with larger 3.000-inch main journals (which made it taller and wider than the 351C) designed to accommodate the 400’s 4.000-inch stroke.

      The 400 debuted for 1971 to replace the 390/428 FE big-block in full-size Fords and Mercurys. For manufacturing cost efficiencies, more than anything else, Ford destroked the 400 to 3.500 inches to achieve the 351M for 1975.

      The 400 Cleveland is a “square” engine, meaning it has the same bore and stroke dimensions. The tall-deck 400/351M has 351C-2V heads with huge, open 76.9-cc chambers, which makes them a poor choice for any Cleveland engine project because they lose compression and are prone to pinging and detonation due to poor quench.

      Another important issue to remember with the 400 and 351M engines is their bellhousing bolt pattern. Most 351M and 400 blocks have a big-block bellhousing bolt pattern like the 385-series 429/460 engines. However, some were produced with both the big-block and small-block patterns, making them compatible with both types.

      Although the 400/351M has a reputation for being a low-emissions slug from the 1970s, it is capable of making incredible amounts of power when fitted with 351C-4V or good aftermarket cylinder heads and induction. And if you’re going to build a 351M, fill it with as much displacement as possible for best results.

       Small-Block Ford Dimensions & Weights

       Ford Small-Block General Engine Specifications