An intake manifold is more than the plumbing that connects the carburetor or throttle body to the ports in the cylinder head. It is an integral part of the induction system that has to match the airflow characteristics of the cylinder head and camshaft, as well as the displacement and rpm range of the engine.

A well-designed manifold that is properly matched to the engine’s requirements will make more torque and horsepower than a manifold which is mismatched to the engine.

Stock intake manifolds are often a compilation of compromises. Stock manifolds are typically designed to minimize manufacturing cost, to accommodate emissions fittings, to fit a tight engine compartment with limited hood clearance, and to provide good low- to mid-range performance, fuel economy and emissions. Most stock engines spend 95% of their running time between idle and 3,000 rpm, with rare bursts above 5,000 rpm.

Consequently, if the engine is modi...