Horse power limit with exhaust manifold 318

Eworth, think of the engine as a giant air pump.

It's a 3 inch pump with a 3 inch inlet and a 3 inch outlet.

If you do anything to increase the efficiency of the pump, ie.,improve flow or replace heads, cam, , compression etc. or just replace with larger pump (engine), say a 4 inch pump (360) you're still restricted by a 3 inch outlet.

If you increase you inlet to 4 inch, by replacing the intake manifold, carb, etc.

You are still running a 3 inch outlet.

Back in the day, the most cost efficient way to increase H/P was headers, cheap 10% hp for $125.

hope it helps..