Exactly how does a performance camshaft perform better giving more horsepower?

Without going to deep into camdesign semantics I suggest the following, in general:

1 Let's name the area limited by; outer dia of the valve x the valve lift, the "flow-window" or flow curtain"

2 The larger this flowarea at max lift the larger the POSSIBLE flow from a specific cam. This improves generally the overall performance.

3 Larger flowarea can also be gained by letting the valve stay open longer (=duration). This does usually improve the torquecurve in the upper rpm and consequently less torque in lower rpm...

If higher airflow is possible the combustionpressure = torque = bhp might be higher and/or fall less in upper rpm, if the set-up is properly.

This improves the performance

A little more advanced definition of camshaft function could be as follows:

The cam area is the area beneath the valvelift curve and above the clearanceline.

This area, which is directly correlated to the possible flow a certain cam might allow, is possible to enlarge in a few ways:

1 More valvelift, no real disadvantages...

2 Higer valve accelerationrate/deceleration, more strain

3 More valveopening time, duration, lifts the performance upwards and weakens the lower range...

Then ther is another area, the overlap:

The overlap, and corresponding overlap area, decides how high up in the rpm the flow might continue; with a lot overlaparea the engine is weaker in bottom rpm and, yes, stronger up, and with less overlaparea the opposite.!

N.B. The engine might utilize higher flowrate out of a camreplacement ONLY if the rest of the flowsystem (from the airfilter to the exhaust tailpipe end...) allows it, in general...

BR

M.Aaro