As above, therefore, when you increase the duration of the valve opening on the cams, you are increasing the amount of time that air can be flowed, and thus the volume efficiency. Likewise, as the lift increases, same deal.
there is a fine balance between valve duration, go too much and you'll be pumping nice air straight into the exhaust because your valve overlap has increased! (both valves open at the same time) of cause you can increase cam seperation angle, but this also has downfalls, (moving peak power up higher)
cams are a twat in a 4 stroke engine
