How to choose a camshaft

While is is true that you cannot change the lobes of a camshaft after it is ground (unless you weld and re-grind the lobes), you can alter the characteristics of the camshaft in your motor by installing it in either a retarded or advanced position relative to the crankshaft rotation. For instance, the manufacturer recommends the camshaft to be installed straight up, neither advanced or retarded from the as-manufactured design. However, you have determined that you are making too much horsepower down low and can't hook the tires up. You want to trade off a little of the lower end power for some higher end power. In this case, you might install the camshaft slightly retarded. Although all four events (intake valve opening, intake valve closing, exhaust valve opening, exhaust valve closing) will be affected by changing the camshaft phasing, the most important one will be the intake closing point. If you retard the camshaft, you will be closing the intake later, thus bleeding off some of the cylinder pressure and resulting in less low end power. Vice versa if you advance the camshaft. More bottom end, less top end.