What besides the following affect horse power (BHP)?
Displacement:
stroke vs bore
RPMs
Compression Ratio
Air Flow:
intake vs exhuast
Inline vs "V" shaped
Gear
In the beginning was the Word,
and the Word was with God,
and the Word was God.
He was with God in the beginning.
And all things that were created were created through Him, and anything that was not created, has not been created. John 1:1-3
BHP (Brake Horse Power) is a measure of the power produced at the output point of an engine (usually a dyno brake).
BHP is defined by the formula: (bmep(psi) x displ(cu.in.) x power cycles per min) / 396,000. So to increase BHP, you can do it by increasing bmep, displ or rpm.
Increasing BHP by increasing rpm is usually the least efficient approach, because friction losses (pumping losses and mechanical friction losses) tend to increase exponentially with speed.
Increasing displacement, as long as you do not increase the number of cylinders, works well because volume increases as the cube of the dimension while surface area increases only as the square of the dimension. Thus decreasing heat transfer losses to the coolant. A small number of cylinders for a given displacement also minimizes the total linear dimension of gas seals (piston rings) exposed to combustion pressure.
Increasing BMEP is usually the most difficult option, since it requires either raising the compression ratio or increasing the cylinder pressure at the begining of the compression stroke (supercharging). With a spark ignited engine cycle, you will always be limited by detonation.
The basic question you ask comes down to this: How effective is the engine at converting the theoretic power available from combusting a fuel (about 19,000 Btu/lb LHV for gasoline) into usable power? (and a horsepower is equal to 2545 Btu/hr). Engine design is an excercise in compromise, and the best design for a given application is the one that best balances the (usually conflicting) requirements, for weight, power and efficiency.
