Words And Photos: Richard Holdener

Ford performance is all about the modular engine family now with its killer Coyote sporting dual overhead cams, variable cam timing and electronic fuel injection, but times were different back when Clevelands roamed the earth. The canted-valve Clevelands reined supreme in everything from drag racing to the high banks of NASCAR. What did the Cleveland motors have that the competition didn’t? The answer to that question was head flow.

Sporting the famous Cleveland heads, the 351C family (and smaller Boss 302) were blessed with more head flow than any other production Ford small block before or since. It took the introduction of the 5.0L Coyote to knock the Cleveland (specifically the 1971 Boss 351) from the top spot as the most powerful production small block ever offered by Ford. As good as the Clevelands were in stock trim, they were just scratching the surface of the potential awaiting in those cavernous cylinder head ports. What every Cleveland needed (then and now) was the right cam and intake package to Go With the Flow.

To illustrate just how much power was lurking in a stock Cleveland, we assembled one for testing. Starting with a 2-bolt, 4V Cleveland core motor, the block was treated to the usual machine work courtesy of L&R Engines in Sante Fe Springs, California. The machine work included boring the cylinders .030 over to make room for eight new slugs from Probe Racing. To help improve power, the forged pistons featured small domes that pushed the static compression to 11.0:1.

The Probe pistons were designed to run on the factory connecting rods, which received polishing, shot-peening and a set of ARP rod bolts. Spinning the upgraded rods and new forged pistons was a cast 351C crank. The factory crank was first polished then balanced with the entire reciprocating assembly that included new Clevite rod and main bearings. We finished up the short block with a reproduction (hydraulic flat-tappet) 351 Cobra Jet cam profile courtesy of Elgin cams. To ensure maximum protection during break in, the hydraulic flat-tappet cam was installed with a liberal dose of moly assembly lube on the lobes (and bottom of the lifters). We also took the liberty of adding high-zinc, break-in oil from Lucas Oil.

The crowning glory of any 351 Cleveland was obviously the big-port, canted-valve cylinder heads. Heads for the 351C test motor also came from our 1971 4V core motor. Originally a standard 4V 351C, these 1971 heads featured the desirable (smaller) quench chambers, but missing was the adjustable valve train offered on the solid-cammed (hard to find) Boss 351 heads. No worries, as this situation was easily cured with a little machine work. L&R machined the non-adjustable pedestals to accept rocker studs and guide plates.

Truth be told, we could have run the hydraulic flat-tappet COMP cam with the non-adjustable valve train, but we liked the adjustability and wanted to install roller rockers after this test. Additional upgrades to the 351C heads included new stainless steel intake and exhaust valves from Streetmaster. The factory multi-groove valves were replaced with the more common, single-groove variety and treated to a multi-angle valve job. We also took the opportunity to mill the heads produce 63cc combustion chambers. The iron 351C heads were installed onto the awaiting short block using Fel Pro head gaskets and ARP head studs. Fel Pro also supplied the necessary intake gaskets as well.

To illustrate the changes in the induction system, we topped the Cleveland with a factory 4V intake. Originally designed to accept an Autolite carburetor, a simple gasket and spacer allowed us to substitute a 750 HP Holley. Additional components used on the dyno included a Meziere electric water pump, MSD ignition and 1 7/8-inch Hooker Super Comp headers. Run with the stock intake and cam, the 351C produced peak numbers of 359 horsepower at 5,700 rpm and 372 lb-ft of torque at 3,800 rpm. 

Judging by the results, the factory intake and cam were designed with torque in mind. After our baseline, we replaced the factory cam and iron intake with a COMP XE284H cam and Edelbrock Performer RPM Air Gap intake. After swapping in the new cam and intake, the peak power numbers jumped by nearly 100 hp to 452 hp at 6,500 rpm and 412 lb-ft of torque at 5,200 rpm. Torque production was way up, as the new combo offered over 400 lb-ft from 3,650 rpm to 5,550 rpm. Only below 3,300 rpm did the new combo lose out to the stock stuff. The amazing power gains offered by the cam and intake swap showed just how much power was waiting to be unleashed (in the Cleveland heads) when you decide to Go With the Flow.

The 351C, especially the 4V variant, was blessed by the factory with huge ports that flowed plenty of air. What any stock Cleveland needed was the right intake and camshaft to go with the head flow. To illustrate this, we ran a rebuilt 351C with a reproduction of the stock 1971 Cobra Jet cam (already a step up from the standard 4V cam) and factory cast-iron intake. In stock trim, the 351C produced 359 hp at 5,700 rpm and 372 lb-ft at 3,800 rpm. After installation of the COMP XE284H cam and Edelbrock Performer RPM Air Gap intake, the power numbers jumped to 452 hp and 412 lb-ft of torque. Note that both peak hp and torque occurred higher in the rev range with the new cam and heads, but only below 3,300 rpm did the new combo lose out to the stock stuff.

Sources

Probe Industries
probeindustries.com

Comp Cams
compcams.com

Edelbrock
edelbrock.com

L&R Automotive
lnrengine.com

Holley/Hooker/Weiand
holley.com

Speedmaster
procompelectronics.com