its seat, a camshaft once again cannot do this too fast or the valve slams into the valve seat (sometimes valves even bounce off the seat). Most modern cam designs optimize valve acceleration rates by designing camshafts with asymmetric lobes. This style of lobe lifts the valve faster than it lowers the valve. Quite simply, asymmetric lobe designs can be utilized to maximize the performance available while increasing the durability of the valvetrain.

Types of Engines
There are two basic styles of piston engines in production today, the overhead-valve engine (OHV) and the overhead-cam engine (OHC). Overhead valve engines rely on valve lifters, pushrods, rocker arms and a camshaft which rests in the engine's cylinder block. Examples of OHV engines include most of the domestic V8 and V6 engines manufactured over the last 50 years.

Knowing the Specs
Since we have already explored the basics of camshafts, we will now attempt to unlock the mysteries surrounding camshaft specifications. Since the camshaft(s) influence when an engine starts making power, when it stops producing power, maximum power output, fuel economy, idle quality, and engine efficiency, it is important to understand camshaft specifications. With this basic understanding, you will be better able to select the camshaft(s) that will keep you ahead of the competition.

Lift and Duration
The basic function of a camshaft is to open and close the engine's valves. On many applications, a single camshaft controls the opening and closing events of all the valves in an engine. Other applications may implement as many as four camshafts to control the valve events. Regardless of the number of cams, the rules that apply for single camshaft engines also apply to those with multiple camshafts. The most well-known camshaft specifications are lift and duration. Most manufacturers give specifications for lift at the valve, instead of at the camshaft. On some applications that don't use a

Valve Lift = Lobe Lift x Cam Follower Ratio

Lift
Lift is nothing more than a measurement of the maximum distance the valve is opened. Assuming all other specifications remain the same, choosing a camshaft with more lift will increase the flow of air and fuel into an engine and the flow of exhaust out of an engine. As a result, more power can be made. In many cases, camshafts that have increased lifts over stock specifications and near stock duration will offer increased performance without making measurable sacrifices in "driveability". Everything has a limit and cylinder heads will generally reach a point where airflow no longer increases with an increase in valve lift. Before you order that mega-lift cam, please consider the following: when valve lift is dramatically increased, the possibility of valve to-piston contact, coil bind at the valve spring and valvetrain interference is also increased. To avoid bent valves, broken retainers and thin wallets, always use the necessary complimentary valvetrain components and check valve-to-piston clearance when recommended by the camshaft manufacturer.

Duration
Along with how high a valve is opened, how long it remains open also influences the performance of an engine. If you are trying to fill a glass at the sink, how much you open the faucet or valve, as well as how long you have that valve open will determine how much water fills the glass. How long you keep the faucet turned on is a simple measure of duration. The duration specification of a camshaft is measured in crankshaft degrees of which there are 720 in one complete four-stroke cycle. However, the problem with camshaft duration figures is that different manufacturers measure this duration at different valve lifts. The Brand-A manufacturer might measure duration as soon as the valve is lifted .015 of