Engine Rebuilding: The Camshaft

In spite of all the talk these days about engine management of the electronic kind, the camshaft is still calling most of the shots. Virtually every parameter such as peak torque, a usable power band, peak horsepower, manifold vacuum, fuel mileage and more are determined by the cam's timing specifications. No other single modification can produce as much horsepower per dollar. No other single modification can cost you as much power, efficiency and driveability if you select the wrong cam.

First Steps
So where do you start when selecting a camshaft for your resto or restomod project? If you're doing a restoration by the numbers, obviously you need a cam with factory specs. If the factory has discontinued grinding the cam that you require, chances are one of the larger cam companies are reproducing them or grinding one with similar specs. Most companies have comprehensive catalogs and excellent tech lines to guide you in the right direction. The information they provide includes the usable rpm ranges and recommendations for other changes that suit the camshaft such as lower gears, a high stall torque converter, exhaust headers or a larger carburetor.


If you are interested in the restomod approach for upgrading the power and efficiency of your vintage engine, then you can take advantage of more modern grinds that produce more torque and horsepower by opening and closing the valves faster within the same duration specification. Not all 280-degree camshafts perform the same. If you open the valve faster and close it at a faster rate, hence later, the camshaft thinks that it has more duration than it actually does. Adding more duration to a camshaft tends to reduce low-end torque and driveability. Opening and closing the valves at a higher rate does not and provides more effective duration.

Duration
So what's the practical limit for most restored engines without special modifications to accommodate the camshaft? Most engines respond well to cams with "advertised" durations of 260-270 degrees of duration. A more scientific method of measurement is duration measured at .050-inches of valve lift. Here you are talking 215-220 degrees of duration. Anything more and manifold vacuum drops to where the power brakes don't work too well and the engine is pretty sluggish off the line.


Duration isn't the only camshaft specification that's important to watch. Lobe separation angle, often referred to as the camshaft centerline, makes a significant difference in the way cams perform. Most resto cams are ground on 110-112-degree centerlines, a good compromise of power and fuel efficiency. Some drag race cams are ground on 104-106-degree centerlines to produce more mid-range torque, but they require many other mods to work successfully.