On stock engines, the OE cam is designed for an optimal combination of usable power and fuel economy given the available equipment options: transmission type, rear gear ratios, tire size, and computer system (you'll find, for example, that stock automatic transmission applications can't handle radical cam profiles as effectively as manual transmissions. Most aftermarket cams listed for use with automatic trannies are in the mild-street class). You might want to customize your engine's output and usable powerband to meet specific goals. For example, you can select an aftermarket cam to deliver an overall boost in horsepower without significantly altering the powerband. You may want to get a cam to complement a change to a higher rear gear ratio or different tires. You also may want a cam to deliver more low-end torque for improved stoplight launches or for better horsepower at higher speeds. The possibilities and combinations seem limitless (even though they're not) and would take more space than we have here to thoroughly cover the subject. That's why we recommend you talk to your manufacturer before you make a purchase.
All of the cam manufacturers covered in this story have someone in its technical department you can call who can help you select a cam that fits your needs and equipment. Not only can they tell you the best cam to purchase given your intended driving needs, previous modifications, and drivetrain and tire sizes, they can also point out problem areas that may arise with a specific cam choice (such as the need for higher-rate valvesprings, guideplates, spring retainer and oil seal interference, shorter pushrods, retainer-to-valve clearance, rocker studs, and whether you should pay close attention to piston-to-valve clearances or not). We attempted to select cams that can be installed without further engine (intake/ exhaust) or driveline (transmission/rear gear) modifications.
Also, note some of the cams (OK, the majority) listed here aren't emissions legal for street applications (we attempted to note the ones which are). Keep this in mind when you're looking for your upgrade.
Camshaft Specification Glossary
Peak torque rpm: The rpm at which a specified cam delivers peak engine torque. Theoretically, cams operate at maximum efficiency only at a specific engine rpm. Performance falls off at anything above or below that rpm.
Peak horsepower rpm: The rpm at which a specified cam delivers peak engine horsepower.
Basic rpm range: The engine rpm range at which a specified cam delivers optimum performance. Generally speaking, the more radical the cam in terms of lift, duration, and overlap, the higher the basic rpm range.
Advertised duration: The degree of crankshaft rotation the intake and exhaust valves are actually open. Because of the gradual ramping up and down of the valve lift, it's difficult to precisely determine the beginning and end of lift, even though this is what advertised duration attempts to do. Because of this-and a need to provide a standard industry-wide-manufacturers also list cam "duration," or "duration at 0.050 inch."
Duration (or duration at 0.050): For standardization purposes, most manufacturers rate cam duration at 0.050 inch of tappet lift. Thus, duration refers to the amount of crankshaft degree rotation in which the valves are open (from 0.050 inch on the opening event to 0.050 inch at the closing event). Reading the duration numbers can tell you a lot about a cam's performance. In general, the lower the comparative duration, the more likely peak power will be lower in the rpm range. As duration increases, power shifts to the upper rpm range. Naturally, the trade-off is that as you gain upper-end power, you lose low-end power.