Lift off: Valves are pushed by the
lobes on the camshaft. How far they
are pushed is called “lift.”
WHAT IS “VALVE LIFT”? Dear MXA, MXA is always talking about valve lift and how a cam has 0.5mm more lift or 0.5mm less lift. It sounds very important, but what does it mean? Valve lift is determined by the height of the lobe on the cam. Lift is how far the valve is pushed down into the combustion chamber. Valve lift determines the air velocity in the intake system. Think of intake valve lift as a window into the combustion chamber. If you open the window wider, more air and fuel will flow in. If you don’t open the window as much, less air and fuel will flow into the combustion chamber. The higher the lift, the more the engine will breathe. This is good if you want more power at higher rpm. Paradoxically, more lift also means your engine takes longer to develop power. Too much lift and the air will break away from the surface of the valve and create turbulence. Air gets turbulent when the lift is higher than 15 percent of the bore. Too little lift will restrict airflow. Less airflow translates into less power. Exhaust valves do not have air-separation problems, so the lift can be higher, allowing for smaller exhaust valves. Exhaust valve lift can be 20 percent of the bore without losing effectiveness.