Camshafts and High Camshafts explanation

If cylinder heads and blocks are the heart of an engine, then the camshaft and valve train have to be the brains of the operation apart from the ECU that is. Exact timing of the opening, closing, lift, and duration of each valve is essential to increase the power and torque of engines.

A valve train would consists of valves and a mechanism which opens and closes them. The opening and closing system is called a camshaft. The camshaft uses lobes (cams) that push against the valves to open them as the camshaft rotates, the springs on the valves then will return them to their closed position. This is a critical job, and can have a great impact on an engine's performance at different speeds.

The key parts of any camshaft are the lobes. As the camshaft spins, the lobes open and close the intake and exhaust valves in time with the motion of the piston. It turns out that there is a direct relationship between the shape of the cam lobes and the way the engine performs in different speed ranges. 

When you increase the RPM, the 10 to 20 RPM configuration for the camshaft will not work very well. Just say if the engine is running at 4,000 RPM, the valves are opening and closing 2,000 times every minute, or 33 times every second. At these speeds, the piston is moving very quickly, so the air and fuel mixture rushing into the cylinder will also be moving at a very quick rate.
When the piston starts its intake stroke and the intake valve opens, the air/fuel mixture in the intake runner starts to accelerate into the cylinder. By the time the piston reaches the bottom of its intake stroke, the air/fuel mixture is moving at a pretty high speed. If you were to slam the intake valve shut, all of that air/fuel mixture would come to a halt and will not enter the cylinder. By leaving the intake valve open a little longer, the momentum of the fast-moving air/fuel mixture continues to force air and fuel into the cylinder as the compression stroke is started by the piston. In theory the faster the engine goes, the faster the air/fuel mixture flows and the longer we would want the intake valve to stay open. We would also want the valve to open wider at higher speeds. Also affecting the cams performance is lift, the duration, overlap and timing.

Lift
Lift refers to maximum valve lift. This is how much the valve is "lifted" off its seat at the cam lobe's highest point. The intake and exhaust valves need to be open to let air/fuel in and exhaust out of the cylinders. Generally, opening the valves quicker and further will increase engine output. Increasing valve lift, without increasing duration, can yield more power without much change to the nature of the power curve. However, an increase in valve lift almost always is accompanied by an increase in duration. This is because ramps are limited in their shape which is directly related to the type of lifters being used, such as flat or roller.

Duration
Duration is the angle in crankshaft degrees that the valve stays off its seat during the lifting cycle of the cam lobe. Increasing duration keeps the valve open longer, and can increase high-rpm power. Doing so increases the RPM range that the engine produces power. By increasing duration without a change in lobe separation angle will result in increased valve overlap.

Overlap
Overlap is the angle in crankshaft degrees that both the intake and exhaust valves are open. This occurs at the end of the exhaust stroke and the beginning of the intake stroke. Increasing lift duration and/or decreasing lobe separation increases overlap. At high engine speeds, overlap allows the rush of exhaust gasses out the exhaust valve to help pull the fresh air/fuel mixture into the cylinder through the intake valve. Increased engine speed enhances the effect. Therefore increasing overlap, increases top-end power and reduces low-speed power and idle quality.