September 14, 2005

OK, we admit it. We haven't been giving the 351 Cleveland enough ink lately. Seems everyone is building the venerable 289/302/351W small-block, which our readers love because they're plentiful and easy to build. That makes it easy for us--perhaps a little too easy.

Ford's legendary 351C middle-block was a back-door surprise for 1970. In 1969, Ford introduced the raised-deck 351 small-block we came to know as the Windsor. It looked similar to the 289/302, but it was a pinch wider, a hair taller, long on torque, and ready to make unrealized power. Then, scarcely a year into production, the 351W had company: the more powerful close cousin with the same displacement in the form of the 351 Cleveland. It's often been asked, why the same displacement from a different engine family? There have been a lot of theories, but so far no concrete answers from anyone who was there to see it unfold firsthand. We'll kick around some solid theories later in this article.

The 351W was little more than a raised-deck 289/302ci V-8 with the same 4.000-inch bore, but half an inch more stroke than the 302. It also had similar cylinder-head castings with slightly larger valves and ports. The 351C's 4.000-inch bore and a 3.50-inch stroke was dimensionally the same as the 351W, but it differed in block design and large-port, poly-angle-valve heads. The large-port heads were designed to flow better at high rpm, allowing the 351 middle-block to make extraordinary horsepower and torque on the racetrack. On the street, the 351C wasn't the powerhouse it was on the track because the oversized ports didn't yield the velocity at low rpm necessary to make good torque. This was certainly true with the 351C-4V and Boss 351 engines. In 351C-2V applications, low-end torque was improved, thanks to smaller valves and ports. But the 2V heads suffered from combustion-chamber shortcomings that caused excessive spark knock and reduced compression.

When building a 351C, it's a good idea to know how to amass the right parts to make the most of your buildup. We're going to show you how to coax more horsepower and torque from a 351C without having to sell the farm.

The Right Stuff

Formula For Success
Engine building isn't always just about engine building; it's also about choosing the right parts. Building a healthy street Cleveland involves choosing the right heads and induction system, which is key with the 351C. Choose a single-plane manifold and 4V heads with a 351-inch bottom end, and you can forget low-end torque. A single-plane manifold with 4V heads makes its power at high rpm. And that means peak torque around 6,000 rpm, not at 3,500 rpm where you need it most on the street.

The 351C-2V head is more appropriate for street use because it has smaller ports and valves, which moves peak torque down where we need it most: at 3,500 rpm. Choosing the right camshaft profile and dual-plane intake manifold improves driveability tenfold. Torque comes on crispy and strong as the engine spins through 2,500-4,000 rpm. The downside to the common U.S.-built 351C-2V head is its wide-mouth open chamber. You get good quench with this chamber, but lousy dynamics because it tends to create two flame fronts under hard acceleration, which causes spark knock (pinging).

The best Cleveland head on the planet is the Australian 351C, with the best combination of ports and chambers: the 351-4V wedge chamber and the 351C-2V ports for better low and midrange torque. PowerHeads is your source for the Aussie Cleveland heads, which are supplied ported and fitted with hardened exhaust valve seats. It's the perfect Cleveland street head.

Speed-O-Motive builds its 351C much the same way it does small-block 289/302s. Oil galleries get a workout where necessary. Oil return flow is improved to ensure sufficient oil in the pan. Press-in oil gallery plugs are tossed in favor of screw-in plugs.

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The Aussie Connection: PowerHeads
PowerHeads can set you up with Australian 351C heads that are ported and steel seated for optimum performance. The Aussie Cleveland head has the 351C-4V wedge chamber, coupled with "right-sized" ports for great low and midrange torque resulting in good street performance. The 351C-4V chamber offers good quench, coupled with a tight wedge design for reduced detonation. A little bit of work around the intake valves improve flow. PowerHeads works the ports and bowls, which will help your 351C make more horsepower and torque. You can get into these guys for under $1,000.

Cleveland: The Knudsen Connection
We have long accepted the 351C as a small-block Ford, although its weight and size tend to make it more a middle-block--a small-block with larger heads that makes big-block power. However, the 351C's basic architecture says "small-block Ford" with identical bore spacing and size.

Where the 351C block differs is the wraparound iron timing-set compartment, steel timing cover, and a 12/6-o'clock fuel-pump bolt pattern. At first glance, the front of the 351C/351M/400M block resembles the Oldsmobile Rocket V-8s of the era. All had a wraparound timing compartment with a steel cover and 12/6-o'clock fuel-pump bolt pattern.

Here's a loose theory we wish we could confirm. Did Bunkie Knudsen and the engineering people he brought over from GM spearhead the 351C? Semon E. "Bunkie" Knudsen was hired away from GM's Pontiac Division by Henry Ford II in 1967-1968 to run Ford Motor Company. Key events in Ford history were the result of Bunkie's involvement at Ford: the '69-'70 Boss 302 and 429, '71 Boss 351, '69 Talladega/Spoiler II, bolt-on front fascias, and the pucker-mouth '71 Thunderbird and '72 Torino with the Knudsen "Pontiac" nose.

Did Knudsen influence Ford history underhood? Is his influence the reason there were two 351ci engines? We can envision a huge political struggle between Knudsen's people and Ford's people at the time: Knudsen's people for a revised 351ci engine (ultimately called "Cleveland") and Ford's people in favor of staying with the 351W.

When you study the 351C's architecture with its Oldsmobile-like iron block and big-block Chevrolet-like canted-valve heads with huge ports, could Knudsen's influence have been far behind? What's more, take a good look at the 385-series big-block Fords--the 429 and 460. Note the wide canted-valve heads and block design. Then, study the 396/402/427/454ci big-block Chevrolets. Note the similarities in the two designs. Aside from the front-mounted distributor, the Ford big-block is virtually identical to the big Chevy. Can anyone out there help us solve this mystery?