Reply to "Seeking Stroker Kit selection advice."

Arno

The limits of the production short block under racing conditions is 450 bhp, 7200 rpm (about 4200 FPM mean piston speed), and 8:1 dynamic compression. Race conditions means the engine is operated WFO down long straight-a-ways lap after lap. Sure owners get away with engines making more power, but not under racing conditions. A street engine is operated 99% of the time at part throttle, and an engine operated at part throttle is not producing anywhere close to its maximum compression or horsepower. Drag racers get away with more power, but the experienced ones know that to go racing with an engine employing the production block making anything close to 500 bhp will require grout in the water jackets. Grout is a viable solution for drag racing, but not for circuit racing. Grout is not ideal for street cars either as it makes the oil run hotter.

The cylinder walls of the production block are the main problem. After that I'd say the connecting rods are weakness #2. The lubrication system is problematic but it is well known how to fix it. The production crank is good for abuse into the mid-7000 rpm range, but since it is not fully counter-weighted it should never see use into the 8000 rpm range. For constant high speed use the crank is normally internally balanced.

The short block assembly of a typical professional level 351C racing engine in the 1970s did not employ production parts, it was assembled completely from non-production parts. A heavy-duty racing block cast by Ford with thicker cylinder walls and thicker bulkheads was available from contractors formerly associated with Ford’s racing programs (Bud Moore Engineering, Gapp and Roush, Holman and Moody, and Bill Stroppe). A fully counterweighted forged steel crankshaft manufactured by Moldex was available from the same contractors. Another fully counterweighted billet steel crankshaft manufactured by Hank the Crank (HTC) was available via the aftermarket. Chromoly connecting rods with doweled caps fastened by 7/16” cap screws and forged aluminum round skirt pistons were available from several aftermarket suppliers. The engines were equipped with tappet bore bushings and lubricated via dry sump style lubrication systems when the rules allowed them.

Someday we hope to have a new heavy duty Cleveland block available, for now to go racing with a Cleveland its best to hunt down an old NASCAR block; or build a hybrid combining a heavy duty 351W block with a 9.2 deck height, with Cleveland heads … what we call a Clevor.

Outside of the durability issue there is certainly no problem building a 351C circuit racing engine making 500 to 550 bhp. The iron heads were made to support that much power in the 7000 rpm range with a single 4 bbl carburetor, a single plane intake manifold, a good open exhaust, and a solid flat tappet camshaft with 250 degrees duration and lift in the 0.600 range. For circuit racing I'd set the lobe centers at 112 LSA. If you're using the stock crank use some aftermarket chromoly 351W rods (5.956 length) and round skirt forged pistons. A nice heavy fully bonded damper on the crank snout and a light weight steel flywheel in the back (Yella Terra). Tappet bore bushings (Cleveland block), dry sump lubrication, and an oil cooler to handle lubrication.


-G