The Inside Story of Ford's Incredible 427 SOHC
by Tom Shaw
Ignition was state-of-the-art for that period—dual, low-mass points operating with a transistorized amplifier. Plug wires used stainless steel cores and silicone jackets.
Two cylinder heads were designed. The first appeared in the initial wave of publicity photos, and was distinguished by the spark plug wires entering the head just above the exhaust manifolds. Second Generation heads included important revisions which, among other things, raised the spark plugs to the other side of the head, very near the intake manifold.
In its purest sense, a hemi engine features a spark plug directly in the geometric center of the combustion chamber, but that wasn’t possible with the SOHC design since the camshaft and its related mechanisms were directly overhead. Engineers for the First Generation heads did the next best thing and moved the exhaust port a bit off center, allowing the spark plug to be as near the center as possible. But doing so required a bulge in the exhaust port that cut into the engine’s output.
Early projections called for 550hp @ 7000 rpm and around 475 foot-pounds of torque. The First Generation heads and manifold came up short, dynoing only in the 510 hp range. For all its exotic engineering, it just wasn’t enough of an improvement over the conventional 427 wedge to justify its existence. Goals were raised and projected output was now targeted at 600 hp, again at 7000 rpm.
Because of the immediacy of the job, First Generation heads were developed without the benefit of flow testing, but when output fell short of the projected goal, cylinder head porting and combustion chamber design were scrutinized. Using flowboxes of plaster and fiberglass, and grinding and claying techniques, a steady stream of improvements was made.
“It soon became apparent,” wrote Faustyn, “that each revision in the combustion chamber area which improved air flow brought the configuration closer to a true hemispherical chamber. It was then assumed that the Second Series of the development program would be based on this chamber with a piston dome to match except for machined flats to clear the valves.”
Machined combustion chambers were also specified for Second Series heads.
Moving the spark plug cleared up the intrusion into the exhaust port, and raising both intake and exhaust port floors within the head redirected air flow to the underutilized tops of the ports and picked up “appreciable” air flow. To the engineers’ surprise, the engine responded better to a nearly T-shaped valve than one with a more cone shape, and following the results of bench testing, exhaust ports were given a “D” profile as they exited the head, with the flat part on top.
The accumulated benefit of these revisions boosted port/manifold airflow from 425 to almost 500 cfm. Likewise, adding a second Holley 780 4V carb shortened and straightened manifold runners and ended fuel separation problems. On the dyno, the results spoke for themselves; at 7000 rpm, output was an incredible 616hp. Revving as high as 8100 rpm on Ford’s dyno revealed no apparent problems and output continued to climb, although this higher hp figure wasn’t published. But looking at the dyno reports and projecting a logical output based on the established hp curve, horsepower would probably have been around 640.
It’s A Hemi
With engine design pin pointed and the limited production run ready to begin, Bill France was summoned to the Detroit Engine Plant to see that the engine which Ford so desperately needed him to smile upon was indeed rolling off legitimate assembly lines.
« Prev Page 4 of 6 Next »
