To really gain hp, you need to put more air into the engine. As it is now, the exhaust is not the restriction point.
You will need to start with the intake ports in the head to free up some air movement, then the intake manifold and carburetor.
Now you have more coming in, but the camshaft is still stock, so it now limits how much air can fill the cylinders. At this point you change to a cam with more lift and duration.
Great, the motor now has all the fuel and air it needs, only the exhaust won't let it out. While cutting on the intake ports, you might as well open up the exhaust ports and add bigger valves.
This in turn means a bigger exhaust manifold is needed. Can't find one, go to header style manifolds, and now, finally you need bigger exhaust pipe. But wait, you didn't increase the rpm in which you drive most in so you still have the same hp and probably less torque then you started with. Not until you raise the rpm, will the extra power come into play.
Joe
