The Inside Story of Ford's Incredible 427 SOHC
by Tom Shaw
Seven objectives were established:
- 1. Utilize the production 427 cylinder block and tooling in its entirety.
2. Design single overhead camshafts with to rocker shafts per bank.
3. Employ roller follower-type rocker arms to eliminate complications of lubrication and metal compatibility.
4. Develop a lightweight, inexpensive chain and sprocket type of valve train drive mechanism.
5. Incorporate hemispherical combustion chambers for optimum valve size and arrangement, and combustion efficiency and port design.
6. Cast the cylinder head from iron as a matter of expediency.
7. Design a simple and flexible induction system for gasoline that could later be adapted to multiple carburetion, supercharging, fuel injection, exotic fuels, etc.
It was a fiendishly clever strategy. Using the existing—and race-proven—427 block cut production time and expense, keeping the accountants happy. Race teams would deal with a known block for which parts were already set up. Displacement would stay at the already accepted limit of seven liters, a norm for USAC, NASCAR, NHRA, and just about every other sanctioning body.
What changed dramatically was everything from the deck up and from the timing chain forward. Large new head castings, wide enough on top to mount a camshaft and a pair of rocker arm shafts, were designed and cast from iron in the Ford foundry. Plans were to switch to aluminum at a later date, but aluminum castings have a higher scrap ratio, and with lots of pressure from management to quickly produce NASCAR’s required minimum, cast iron was the material of choice.
Using overhead cams offered many key benefits over the conventional pushrod valve train. First, doing away with lifters and pushrods greatly reduced the mass that the valve spring had to work against. That makes higher rpm possible, provided the block is up to the task, and higher revs move more air and fuel, creating more power. Cams operate against roller rockers, riding on needle bearings, which in turn actuated the valves via a cap that fit over the expose tip of the valve stem. The caps were of a different thickness, allowing valve lash to be adjusted by changing caps. Needless to say, it was a far more efficient system than conventional cam-in-block designs. More aggressive cam lobe profiles were also possible not too, since roller rockers were part of the deal.
Several methods of driving the overhead cams were available, but each had its drawbacks: Gilmer belts, used to drive blowers, had reliability problems; gear sets were accurate, but noisy and expensive.
“We looked at all kinds of fancy and expensive stuff,” Faustyn recalled, “and talked to some of the experts on chains, and they said, ‘Well, that bicycle chain’s been around a heck of a long time and it lasts forever when designed and used properly. But we looked at that long span on top and said, ‘Holy Mackerel.”
The whole route required a chain six feet long. An adjustable idler accessible behind a removable plate in the engine front cover tensioned it. To prevent the chain from whipping as it crossed the long span between the cam gears, a stamped steel guide lined with nylon was mounted just above the top of the chain. Two shorter sections were used elsewhere in the route. It proved to be a reliable system, though frequent checkups were a good idea.
In place of the conventional cam in the valley of the block, a dummy “cam” was used only to drive the distributor and oil pump.
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