It is the cam shaft that governs the amount of lift that a valve has. The greater the valve lift, then the greater the lift rate will be. With a performance cam (or height lift cam) this lift is increased allowing more FAM into the combustion chamber. This results in greater torque and power at higher revs for more aggressive cams. When the engine is pulling low revs the modified cam would result in a slight decrease in torque. The benefits to be gained by increasing the lift rate and the valve lift are generally greater on a larger engine rather than a smaller one.