But, in addition, you need to be prepared with the right information about your engine and what you ultimately want to be driving. Let us now review some basic cylinder head data that one must consider before selecting a camshaft. Most people will agree with the statement that larger valves are required for more power. But now we need to ask several questions. It has been my experience that when you are dealing with a stock cam, say 250 degrees duration, it does indeed help to increase the valve size to get more flow through the engine.
Some engines respond to increasing the exhaust flow so that it almost matches the intake flow.
Now let's see how these comments have been translated into some popular 1600 Lotus Twin Cam street and racing motors. In the above table, the standard engine is an early Weber head and the Sprint is a late Stromberg head. Flow measurements of the Stromberg, Racing, and Brian Hart heads are shown in figures 1 a-c. As you increase the RPM band, you'll need to increase the compression ratio and add some more duration to the cam. As soon as the duration is above 270 degrees, the standard exhaust system will likely restrict the breathing ability of the engine.