How to Become a Camshaft Expert
Looking to buy a camshaft for your LS engine? Before you buy you may want to learn what some of those terms mean if it’s your first time buying. We’ll show you each term and give you a definition so you can be a better camshaft buyer.
Base Circle – The concentric or round portion of the cam lobe where the valve lash adjustments are made.
Lift – This is the maximum distance that the cam pushes the follower when the valve is open, but is different from valve lift. The more lift a cam lobe has, the more the valve will open. 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.
Cam Lobe – The parts of the camshaft that create the valve movement.
Duration – The length of time that the valve is held off the seat by the cam. This is measured by the degrees that the crankshaft rotates. More degrees of duration will make the engine operate in a higher rpm range. Increasing duration keeps the valve open longer, and can increase high-rpm power. Doing so increases the RPM range that the engine produces power. Increasing duration without a change in lobe separation angle will result in increased valve overlap.
Duration at .050″ – The distance measured in degrees of crankshaft rotation from when the valve is open .050″ far until it is .050″ from closing.
Gross Valve Lift – This is obtained by multiplying the cam lift by the rocker arm ratio. Rocker arm production tolerances can vary this figure by as much as +/- .015″.
Overlap – A situation where both the intake and exhaust valves are open at the same time when the piston is at top dead center on the exhaust stroke. The greater the seat duration is on the intake and exhaust lobes, the greater the overlap will be in degrees. 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. Increasing overlap increases top-end power and reduces low-speed power and idle quality.
Lobe Separation Angle – Lobe separation is the angle in camshaft degrees between the maximum lift points of the intake and exhaust valves. It is the result of the placement of the intake and exhaust lobes on the camshaft. Lobe separation affects valve overlap, which affects the nature of the power curve, idle quality, idle vacuum, etc.