The small block Ford has been in production since 1962, in cubic inch displacements ranging from 221 to 351. As original equipment in the popular Mustang GT; it has been receiving considerably more attention these last few years. The current version shares most of its basic architecture with its predecessors, but has undergone some changes that the engine builder must consider. Below is a brief listing of potential pitfalls and recommendations for assembly of one of these engines.
The greatest shortcoming of the small block Ford is the cylinder head design, which is somewhat restrictive, particularly on the exhaust side. While both Ford and the performance aftermarket have responded to the need for higher flowing heads in recent years, the average small block still responds well to camshaft and head modifications that enhance exhaust flow. In addition, a modification strategy that targets low end and midrange torque, instead of high RPM power, will yield the greatest benefits. Such items as small tube headers. dual plane intakes, lower OEM carburetors, and fairly conservative camshafts are advised for street use. Ford's Mustang GT package successfully used a similar approach, with the emphasis on power production up to about 4500R PM.
When you install a performance camshaft in a small block Ford, pay particular attention to the valve spring and retainer combination used. On some of these engines the factory valve rotator and spring combination barely allow enough clearance for the stock cam, let alone a performance unit. Valve rotation devices are not recommended for performance applications, and should be deleted from the cylinder head assembly. Also be aware that there may be differences in valve spring installed heights on various heads - and sometimes on the same head! The VS896R springs should be installed where a 1.70" height is required, while the VS1555 should be used for a 1.82" height. Do not install these springs at the opposite heights, as performance will definitely be compromised.
Camshafts using the 302 or 351W firing orders are interchangeable, provided that the spark plug wiring is rerouted to match the selection made. Small block Ford engines which are computer controlled are very sensitive to camshaft alterations. This is particularly true of the "speed density" type computer Systems found on late eighties Mustang GT's. Be very conservative when choosing a performance cam for one of these vehicles unless you are prepared to make computer upgrades.
There are two critical clearances that apply to camshaft and valve spring installation. The valve spring must have an additional .060" of travel available at maximum valve lift, and there must be at least .100" of piston to valve clearance. These critical clearances will be affected if you change to the 1.6 to 1 rockers, mill the cylinder heads, or alter cam timing!
Another area of concern is the variety of deck heights with which these engines were produced. The 302 engines from 1973 through 1976, along with the 351 engines built after 1972, have a deck height that is .023" higher than that of units made in other years. Since deck height has a direct impact on the engine's compression ratio, it is important to determine which one you have before ordering parts. It has teen a fairly common practice to surface all blocks to a single standard, so an actual measurement may be necessary, especially if it is unknown whether the engine has been previously rebuilt.
When selecting pistons, be aware that, since these engines employ thin wall castings, most stock type blocks should not be bored more than .040" oversize. Using the popular 351 Windsor heads on earlier 302's will improve airflow, but lowers the engine's compression ratio, so chose pistons accordingly For racing applications we have a new Power Forged piston, P/N L2522F, which features complete CNC machining of all working surfaces, reduced weight, and a two valve relief flat top design. Federal-Mogul also offers unique "Clevorâ€ pistons that permit use of "Cleveland two barrel" type heads on a standard 302 or 351W block, an uncommon conversion with great performance potential.