Cam setting is based on the overall combo.From the engine build to drivetrain gearing,chassis and desired power range,using weight,HP&torque,gearing,tire size,shift rpm,trap rpm and calculated MPH.Other reasons maybe for piston to valve clearence and cylinder volume pressures.That a cam should be advanced or retarded,you must analyze your complete combo and calculate where your power and torque curve will best benifit your antisipated performance.