(Part 1 covers the history and design of the 335-series engines. Part 2 provides details on the specific variations of the 351C, 351M, 400 and Australian 351C and 302C).
The American auto industry was dominated by the high compression overhead valve V8 engine from the 1950s to the 1970s . Each of the Big Three, AMC and the Independents released numerous versions of these V8 engines from the late 1940s all the way until 1970. Although General Motors had more engine families than any of the other manufacturers, Ford was a close second. Considering the majority of Ford’s engines were shared between divisions, it is quite astonishing that between 1952 and 1970 Ford released eight different V8 engine designs. Ford’s last overhead valve V8 engine of this period was the 335-series engine, released for the 1970 model year as the 351 Cleveland, followed by the 400 in 1971 and the 351M in 1975.
Like On the Waterfront’s Terry Malloy, the 335-series “could have been a contender” had circumstances been different. It represented some of the Ford’s best engineering and design efforts, but it never saw its full potential. In On the Waterfront, Terry Malloy was a victim of his brother who convinced him to take a fall in a fight, while the 335-series engines were a victim of bad timing and a dramatic shift in the automobile industry. The 351C was at one time quite legendary, especially among Ford high performance enthusiasts, but as time has moved on its legendary mystique has been somewhat lost in the sands of time. Today most Ford enthusiasts default to the common small-block “Windsor” engines.
Although Ford had many engine families, by the 1967 model year it didn’t have anything in the increasingly popular mid-sized V8 displacement range. In mid-1966 Bill Gay was assigned to be the chief engineer of the Engine and Foundry Division. His first responsibilities were to enlarge the 289 to 302 ci and to develop a new mid-sized displacement version of the small-block Ford. Bill Gay chose George Stirrat to oversee the mid-sized engine project. Stirrat determined it was best to increase displacement of the small-block Ford by the lowest cost possible. With a 4” bore in a block with 4.380” bore spacing, cylinder size was already near the maximum. As a result, a stroke increase of ½” over the 302, from 3.0” to 3.5”, was determined to be the best solution. To accommodate this long stroke, a 1.28” block deck height increase was required and the crankshaft main journals were enlarged to 3” for increase strength.
This new engine, called the 351 (but actually displacing 352 ci), was to be produced in Windsor Engine plant #1, hence the eventual name, 351 Windsor. The 351W was added to the Ford line-up for the 1969 model year, and was offered in 2V (for 2-venturis of the 2-bbl carb) and 4V variations (for 4-venturis of the 4-bbl carb).
Early production forecasts had showed that the Windsor plant wouldn’t be able to keep up with demand. The decision was made to expand 351 production to Cleveland Engine Plant #2 and that these Cleveland built 351 engines would undergo a number design improvements. Some historical sources suggest that the 351W was a stop gap to hold Ford over until an all-new mid-sized engine could be developed. This may be why Ford decided that the 351s being produced at the Cleveland plant were to see design improvements.
In early 1968, Bill Gay assigned George Stirrat to head the 351 Cleveland project. Stirrat selected Joe Mucura to work with him. It was sometime during this time of the infancy of this project that upper management decreed this new midsize Cleveland built engine should have a minimum displacement of 335 cubic inches with room for expansion, which is how the engine series got its name.
Mucura and Stirrat had differing ideas on how to build the new engine. Each came up with their own design for the cylinder heads. Mucura’s design, dubbed the 335-M, had large free flowing ports and valves with canted valves, similar to the larger Ford 385-series engines. Stirrat’s design, dubbed 335-S, used cylinder head with inline valves, similar to the 351W, but with larger ports and valves. Of the two designs, Sales, Marketing and Product planning greatly preferred Mucura’s design. It was more innovative and seen as more appealing to the public since it had more high performance potential. Stirrat and Bill Gay were also impressed with Mucura’s design and so it was decided to go with Mucura’s design.
After this decision, Stirrat and Mucura were reassigned. Bill Gay continued to oversee the 335-series project. Gay had the additional objective to make engine assembly easier and to improve quality control. The intake manifold was redesigned to be dry, meaning no coolant flowed through it. This reduced intake manifold heat and potential coolant leaks. The complex timing cover of the 351W, which tended to be hard to seal, was also redesigned. The engineers extended the engine block casting to encase the timing chain. This would allow the timing chain cover to be simple and cheaper piece of flat steel. The block extension allowed for the coolant cross over to be incorporated in the engine block.
The engine itself continued to use the same 4.380” bore spacing of the Ford small block from which it evolved, however, the new design permitted a slightly lower deck height of 9.2” compared to the 351W’s 9.48” deck height. The engine’s lower end was a short skirt design like the Windsor engine, but the main bearing caps and bulkheads were enlarged and strengthened significantly. This stronger bottom end allowed the main bearing diameter to be reduced to 2.75” from 3” used on the 351 Windsor.
Interestingly, after Mucura left the 335-series project, he became involved in the Boss 302 engine project. He decided to take his poly-angle “Cleveland” head design with him and be used it on the Boss 302 engine. The Cleveland head design could be easily retrofitted to the 302, only requiring the coolant passages to be modified. So in essence, the public was able to get a “preview” of the upcoming 351C with the introduction of the Boss 302.
Regular production of the 351C began in July 1969, and the engine was introduced for the 1970 model year in Ford and Mercury cars. The 351C generally replaced the 351W (there were some exceptions) in the intermediate and the pony car lines. It was offered in two variations, the 351C-2V and 351C-4V. In comparing the 1969 351W to the 1970 351C, it appeared that the 351C was a lot of hype for not much return. Both 2V engines had the same 250 hp rating and the 300 hp 351C-4V was only 10 more horsepower than the 351W-4V. Performance tests of the times suggested the two engines performed very similarly. So what was the big deal about this engine? It was all in the state of the art cylinder head design. These heads gave the 351C significant power potential and arguably gave it the most power potential any V8 engine of its time.
Many V8 engines of the era, including Ford’s own Windsor engines, used a wedge combustion chamber. Ford went a different route with the 335-series engines, using a much shallower poly angle combustion chamber, with the valves canted both horizontally and longitudinally. Unlike the wedge combustion chamber, this type of chamber is very efficient and does not have stagnate pockets outside of the main combustion chamber that result in unburned fuel/air. The 335-series combustion chamber promotes excellent turbulence of the air fuel mixture which results in a highly efficient combustion process of the entire fuel/air mixture.
Ford hard started experimenting with poly angle combustion chambers in the early 1960’s and found that it produced a broad flat torque curve. It didn’t produce the highest peak horsepower, but it produced the highest average torque. Ford wasn’t the first to use this type of combustion chamber though. The 335-series combustion chamber was similar in design to Chrysler’s poly-spherical chamber.
Ford produced two versions of the 335-series combustion chambers. First was an open chamber head, which was a shallow open combustion chamber. The second head was the closed chamber, which is where the combustion chamber volume was reduced with small quench areas on either side of the valves. The broad shallow combustion chamber of the 335-series heads creates excellent turbulence and no part of the combustion chamber is shielded from the flame front. The quench area was only used to decrease the volume of the combustion chamber to increase the compression ratio – not to increase performance like when used with a wedge chamber.
It is a common misconception that the open chamber 335-series cylinder head with its lack of quench is more prone to detonation. This is the case with wedge combustion chambers, however, Ford engineers and other experienced 335-series engine experts both agree that the open chamber heads are no more prone to detonation than the closed chamber heads. This is again the result of the thermally efficient shallow combustion chambers used on both styles of heads. Each combustion chamber has its own advantages. The closed chambers have faster combustion at lower RPM compared to open chambers. This results in an increase in low RPM power, but there is no improvement to the mid to high RPM power. The open chambers’ valves are less shrouded, which improves low lift airflow, between .100” and .300” valve lift, in comparison to closed chamber heads. This improved airflow is seen throughout the entire RPM range.
The other excellent design feature of these heads was the poly angle valves. The valve train and valve layout was essentially the same as Ford’s 385-series engines and very similar to Chevrolet’s “porcupine” big block. The poly angle valve layout permitted the 351C to use much larger valves and ports than a typical engine in its size class. The intake and exhaust ports were designed for high flow and low restriction. By canting the intake valve towards the intake port and the exhaust valve towards the exhaust port, it allowed engineers to maximize the port airflow. This layout correspondingly increased the space for the valves allowing for the installation of very large valves.
Unlike the 351W that preceded it, the 351 Cleveland had unique cylinder heads for each carburetor variation. The 2-bbl engines used a “2V” head and the 4bbl engines used “4V” heads. The 2V heads had larger ports and valves than the 351W but the 4V had downright massive ports. They were the largest ports of any small displacement engine of the era and used huge 2.19”/1.71 intake/exhaust valves. With two port sizes and two combustion chamber designs, there were several variations of the 335-series heads.
As we’ve seen, the 335-series engine cylinder heads featured high performance oriented big canted valves, massive ports, and combustion chambers with excellent thermal efficiency. So what was the reason Ford made such a performance oriented head for production cars? At the time of the engine development, Ford was heavily involved in Motorsports. The engineers that designed this engine took all of their past experience learned from Fords Motorsports to design what they deemed to be the ultimate Ford performance engine. The 4V cylinder heads were designed to be a state of the art racing head that was tamed for production engines. The 4V heads were capable of producing 500 hp in NASCAR configurations, and even more power in Pro Stock racers. Even the more conservative 2V heads flowed very well, and could supply enough air to feed an engine with 400 hp.
To get an idea on how well these cylinder heads performed, compare them to another well-known performance cylinder head of the times. The Chevrolet small-block engine was known for its high revving nature and its free flowing heads. The “double hump” heads were for a long time considered the best production castings made by Chevrolet. While they flowed well, the 351C-4V heads flowed significantly better. In the chart below you can see that even non-performance 2V heads are pretty on par to the Chevrolet head, while the 4V head is far superior.
All the great engineering that went into this engine came at a cost. As a result other aspects of the engine were also re-engineered to save money. One area where Ford engineers identified cost savings was the oiling system. Unlike the Ford small-block family, which had three main oil galleries, the 335-series engines were reduced to two. This oiling system sent most of the oil to the cam bearings first and did not give priority to the main bearings on the engine. There were other engines that used similar oiling systems and under most circumstances that production engines would be operated, it was adequate. However, the high performance 351C variants were tuned to run at high RPM and that is when this oiling system could show weakness, resulting in oil starvation to the mains and potentially a bearing failure.
This problem was further compounded by the lifter bores having excessive clearances, causing excess oil to leak out of the lifter bores. This oil leaking can cause oil cavitation from the lifter motion, which could impede oil flow to the mains. That said, engine builders have found various solutions over years to address the oil system and these engines can be made to be very reliable in high performance, high RPM applications.
All 335-series engines all used thin wall casting. This resulted in thinner than usual cylinder walls. Because of this, typically a .040” overbore is the maximum for any 335-series engines, although in some circumstances .060” overbore can be achieved if the block is checked first. In very high horsepower and racing applications, the cylinder walls may not be sufficiently strong. However, Ford cast stronger engine blocks with thicker cylinder walls for NASCAR racing, including one variant that had siamesed cylinders.
By the 1971 model year, Ford had almost fully phased the Ford FE engine out of its automobile line-up. While the 385-series replaced the larger FE iterations, Ford needed something to replace the 390 FE V8. So, it was decided that a larger 400 ci version of the 351C could fill that gap. Using the smaller 351C as the basis would result in a smaller and lighter engine than the 390 FE.
To create the 400, Ford had limited options. Since the 400 was to be based on the 351C, it shared the same 4.380” bore spacing. The 4” bore left little room for further expansion. So it was decided that the stroke would be increased to 4” to create the 400 (which actually displaced 402 ci). To accommodate this increased stroke, Ford had to increase the deck height by over 1” to 10.297”, which was very close to the 385-series deck height. This deck height increase permitted the use of longer connecting rods so the 400 could maintain the same rod-to-stroke ratio as the 351C. However, this also meant that there were less parts shared between the engines. It also resulted in the 400 being slightly taller, wider, and heavier than a 351C. For these reasons, many don’t include the 400 as part of the 351C family. The reality is that the 351C and 400 shares the same basic design and are obviously from the same family. Ford created the 400 from the 351C in the same fashion it created the 351W from the 302.
Interestingly, Chevrolet also created a 400 ci engine from its small block Chevrolet and encountered similar problems to Ford. The Chevrolet small block has a bore spacing of 4.40”, which is nearly identical to the Ford 351C. So there was little room for a bore increase. However, Chevrolet decided to increase the bore to 4.125” by using siamesed cylinders and then it only required a 3.75” stroke to make 400 ci. Even with the shorter stroke of 3.75”, it could not maintain the same rod-to-stroke ratio of the 350 without an increase to the deck height. So Chevrolet compromised the rod-to-stroke ratio, and used a shorter rod in the 400. This allowed for more part interchangeability in comparison to Ford’s 400.
To accommodate the longer 4” stroke, Ford strengthened the bottom end of the 400 with an increase in main bearing size to 3” in diameter. Ford also used a slightly larger piston pin, a unique three point motor mount (as opposed to two point mounts on the 351C) and the larger bell housing pattern of the 385-Series engines. These changes meant that along with the bigger engine block, the 400 used unique rods and pistons, pushrods, crankshaft and associated bearings/caps, intake manifold (due to the extra width), exhaust manifolds (due to the extra height), and engine mounts. The remainder of the engines parts were interchangeable with the 351C.
All Ford 400s were low-performance engines, and almost all had compromised engineering due to Ford’s attempts at trying to meet emissions standards. As such, the 400 has long been painted as a boat anchor smog engine, when it is entirely not the case. While there were no high performance variations, the engine has the same design benefits of the 351C, with the advantage of extra displacement. However, there are a number of drawbacks that have prevented it from being commonly used as a high performance engine.
Ford made one major design compromise to reduce the compression on this engine. The combination of flattop pistons and the same cylinder heads as the 351C-2V produced an unacceptably high compression ratio for regular fuel. So engineers simply increased the deck clearance (moved the piston further down into the cylinder at top-dead-center) to get it to a regular fuel friendly 9:1 compression. The end result was the excessive clearance, twice that of a 351C, and this reduced much of the cylinder heads excellent turbulence. This caused some stagnation in the combustion chamber and detonation was the result with all but mild tuning. This wonky deck clearance measurement stayed with the 400 throughout production.
Until recently, the only solution to correct this excessive clearance was by using custom-made pistons, or modifying 351C pistons to work with a 400 connecting rod. Today, the aftermarket offers pistons with proper deck clearances that also boost compression.
The high performance 4V heads can also be used on the 400, however there is no intake manifold that will fit the larger ports or exhaust manifolds designed to account for the additional deck height. There are aftermarket solutions to these problems, but they aren’t cheap.
As a result of these hurdles, the 400 has not been overly popular as a performance engine, and beyond the late 70s truck crowd, there is little interest in the engine. Nevertheless, those who have taken the time to build a 400 Ford can produce a very potent engine. It doesn’t have the same high RPM capability as a 351C, but has the advantage of a much more robust torque curve. In fact, the engine Builder John Kaase won several Engine Masters Competitions with the Ford 400, beating out traditional muscle car engines such as the Small-block Chevrolet, Ford Boss 429, and Ford FE 427.
The 351C was only in production for 5 years in the North American Market. It was discontinued after 1974 and was replaced by a tall deck 351M, which was a destroked 400. The 351M used the same block as the 400, meaning much more parts sharing occurred which saved costs.
In 1971, Ford of Australia began to produce the 351C in its Geelong plant, along with a small displacement short stroke variant displacing 302 cubic inches. Dubbed the 302C, it was a destroked 351C that shared the same bore and stoke as the 302 V8, but used 335-series engine architecture.
By the early 1980’s 335-series engine production ended in both countries. Like Terry Malloy, this engine had so much potential to be great, to be a legendary engine, but it just didn’t happen. Designed as a high performance engine, by 1971 the auto industry had started to make a drastic shift away from performance to focusing on meeting the ever tighten emission standard. This resulted in compromised engineering being applied to these engines almost immediately out of the gate, simply to allow Ford to meet emissions standards. During this time, Ford was also moving away from Motorsports, ending the need for investment into high performance engineering.
The 335-series engine did have brief moment in the sun with Ford enthusiasts as the 351C-4V, but eventually it would be surpassed by the Ford small-block that stayed in production longer and had far more aftermarket support. We saw a glimpse of this engine family’s greatness in the Boss 351, but ultimately most of the engines from this family were rather ordinary performers saddled with low compression and rudimentary emissions controls. Imagine judging the small block Chevy, or any other V8 of that era, only by its 1970’s variations? Stayed tuned for part two of this series, which will discuss the specific 335-series engine variations in more detail.