what gains should i expect from replacing stock heads with GT40P heads? will there be any machine work that will have to be done?302 with street strip cam,headders,dual plane edelbrock high rise intake,650 edelbrock carb,accel high voltage coil 0.40 over pistions.the heads are F77E

 

Roughly 30% gains across the board.

 

does anyone know a Simple formula for figureing out approxmate horsepower.i would like to figure all aspects into equasion.

 

No.. You can do desktop dyno and approximate it at the crank..