theory, the Tunnel Port cylinder head was a great idea, making a whopping 450 hp at 8,000 rpm. The problem was that racers needed to push it to nearly 9,000 rpm to make checkered-flag power, scattering the engines all over racetracks from coast to coast. Because this problem was epidemic, Ford engineers had to think fast and arrive at a solution everyone could live with to salvage a hard-won reputation for winning.
We will probably never know which came first, the Cleveland engine or the Cleveland cylinder head. But we do know Ford’s engineers took the 351C-4V poly-angle-valve wedge head and used it on the Boss 302-ci engine to achieve peak horsepower in the 6,500- to 7,500-rpm range instead of a rod-snapping 9,000. This was possible thanks to the 351C having the same bore spacing as the 289/302/351W. All it took was cooling passage modifications to these Cleveland castings (because the 351C has a dry intake manifold and the Boss 302 has a wet one), which was easy in production.
Boss 302 engines had 1.73:1 rocker arms mounted on screw-in studs with adjustable fulcrums. All had flat-tappet high-performance mechanical camshafts.
The Boss 302 block began life as the 302 Tunnel Port block with a “C8FE” casting number, four-bolt main caps, heavier webbing, forged steel 3.00-inch stroke crankshaft, heavy-duty connecting rods (actually “C3OE” 289 High Performance rod forgings with broached 3/8-inch bolts and beefy shoulders), and TRW forged aluminum “pop-up” pistons designed for Cleveland wedge chambers. Compression was 11.0:1.
Don’t be surprised to find a “C8FE” block in an early 1969 Boss 302 Mustang because quite a few made it into production cars. The rest were surplus castings left over from the Tunnel Port days that made it into the Ford Muscle Parts program and dealer pipelines.
Other Boss 302 features included a dual-advance dual-point distributor that was a Boss 302 exclusive. On top, the Boss 302 had a 780-cfm Holley 4160 4-barrel carburetor. From 1969 through early 1970, Boss 302 engines were fitted with chrome-plated, stamped steel valvecovers. Early in the 1970 model year, Ford went to cast-aluminum valvecovers. Ram-air was not available on the Boss 302 until the 1970 model year. All 1969 Boss 302 Mustangs were non-ram-air. Ignition systems included a dual-point dual-advance/retard Autolite distributor.
There has been a lot of debate through the years as to why Ford produced two engine families displacing 351 ci: the 351W and 335-series 351C. The 351 Cleveland is a small-block V-8 with the attitude of a big-block thanks to very innovative engineering features. The 351C-4V engine does its best work at high RPM thanks to large intake ports and tight wedge chambers offering good quench. This engine suffers from inadequate exhaust scavenging despite its huge intake ports. Exhaust ports tend to be restrictive considering the generous flow going in. You can do some port work on the exhaust side and gain flow, but don’t expect much improvement.
The 351C-4V has never been very productive with low-end torque because its 4-barrel cylinder heads were designed primarily for high-RPM horsepower and not low-RPM torque. This begs the question why Ford put this engine in car lines not intended for high-RPM use, such as Galaxie, LTD, Fairlane, and Torino. The 351C had a brief four-year production life (1970–1974 in North America). It was never practical for Ford to produce two engine families in North America employing the same displacement. The 335-series Cleveland was more costly to produce than the 351W, which sealed its doom as a mainstream engine in North America.
Ford’s canted-valve large-port Boss 302 engine 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,
