Valves get the bump business from pushrods and rocker arms. Factory rocker arms typically have a 1.6:1 ratio, which means the rocker arm multiplies the cam-lobe lift as something called valve lift. Valve lift is greater than cam-lobe lift.
Being EccentricThe camshaft consists of lobes that convert rotary motion (round and round it goes) into linear (back and forth) motion. The cam lobe emerges from a base circle, which is the shaft's base diameter and circumference. The base circle of a camshaft is also known as the heel, where there is no lift whatsoever. As the camshaft turns, the lifters follow rises in the cam lobes. The maximum amount of this rise is called lift. The cam transfers this lift, via the pushrod, to the rocker arm. The rocker arm not only transfers lift to the valve stem, it also multiplies lift. If our cam lobe has a lift of 0.300 inch and we have a 1.6:1 rocker-arm ratio, there will be 0.480-inch lift at the valve stem. With most Ford small-block and big-block
V-8s, we typically see rocker-arm ratios of 1.6:1. The aftermarket brings us greater ratios, like 1.7:1, which give us even greater valve lift.
When the cam lobe reaches its greatest lift, it's called the nose, located at the peak of the cam lobe. Areas leading up to the nose are called ramps. When we're choosing a cam-lobe profile, not only are we concerned with peak lift, but the shape of the ramps. The ramps determine how quickly the valves open and close. We can ramp quickly up to peak lift, or we can ramp more slowly up to peak. If we ramp quickly, this can give valves and springs all kinds of grief. Ramping up quickly is hard on valves and springs, even though it can be beneficial to performance.