This is a broad outline of the effects of various cam dimensions
DURATION
The duration is the amount of time, measured in crankshaft degrees, which the valve is open. The advertised duration may be measured at a number of points depending on the type of cam and the whims of the person measuring. Advertised duration is a very grey area and should be treated with caution. Its practical purpose is for advertising only. Sometimes the advertised duration may be adjusted so that they are in line with the customers expectations for a particular cam.
The effect of increasing duration is to move the power range to higher RPM.
DURATION AT 0.050”
This is the most accurate and most widely accepted way to measure the cam duration. Increasing the 0.050” duration increases the RPM where the engine has its powerband.
INTENSITY
The acceleration rate of the valve opening is sometimes called the “intensity”. A cam with a high acceleration rate or “intensity” will have a smaller advertised duration and a larger 0.050” duration than a cam with a low acceleration rate. A high intensity cam will often have a higher lift also. The advantage of a high acceleration cam is that it gives a wider power band. The low advertised duration assists in providing good low end power while the high 0.050” duration gives good top end power. The down side to this is that it places a higher strain on the valve train.
VALVE LIFT
Higher valve lift gives an increase in power across the rpm range. This may be achieved by cam lobe design or by the use of higher ratio rockers. This is achieved at the expense of increase wear on valve train components.
LOBE SEPARATION.
The most popular lobe separation is 112 degrees between lobe centres. In general closer lobe centres, often 108 degrees sometimes down to 98 degrees, give a higher amount of power over a shorter operating range. Wider lobe centres 114 up to 118 give less power over a wider range. Wide lobe centres are common in supercharged cars to avoid the valves being open at the same time (valve overlap) thus reducing the amount of air/fuel escaping out the exhaust during the intake stroke. Many of the unleaded engines have wide lobe centres to allow complete burning of the air/fuel mix. Slower burning is a result of low compression.
ADVANCE
In general most engines respond to 2 or 3 degrees of cam advance. The exception is the low compression unleaded fuel injected engines. For race applications the engine can be fine tuned by testing different advance and retard settings. Advancing the cam 4 degrees will usually move the power band about 50 – 100 rpm higher. If you have to go more than 8 degrees to get the desired result you need a different cam !