Where have you been hiding??
The more fuel and air you pass through your engine, the more horsepower
it makes. The more you efficiently burn in EACH STROKE, the greater the
torque. Horsepower is directly proportional to torque and to rpm,
so increasing either (without decreasing the other) will increase your HP.
Normally efficiency drops off with increasing speed but the relationship
varies a lot, depending on things like valve, port, carburetor/intake size
and exhaust size and lack of restriction, and a GREAT DEAL on valve timing.
The wilder your cam the higher the speed at which maximum torque is developed,
but the poorer the performance at low speeds. This can be helped some by
a little restriction in the exhaust (which prevents so much fuel blowing
through at lower speeds, but also at higher speeds, where it also reduces
torque.

This is pretty brief, but that is the essence of the situation.
--
George Downs Bartlesville, Oklahoma