hey, a standard rb20det cam has 248deg intake duration and 7.8mm lift, if you have an aftermarket cam ex. tomei which has a 260deg with 9.15mm lift for every time the valve open its open for a longer duration with more lift so incur there is more air forced into the cylinder every compression stroke of the engine and the exhaust cam has the same effect but lets more air out of the chamber. hope that helps.