Wednesday, December 4, 2013
What Is an Intake Manifold
One of the oldest axioms among car guys is that an engine is essentially a giant air pump. While not technically accurate, this at least gives some idea of how the internal combustion engine works; air goes in, combines with fuel in the combustion chamber, burns and exits as exhaust gas. The manifold is just one of several air-handling devices on the engine.
Manifold Purpose
Derived from the Latin root words for "many" and "fold," a manifold is essentially a chamber designed to distribute air to the cylinders. A manifold has two basic parts, the plenum (central chamber) and the runners (the passages that lead from the plenum to the individual cylinders). Air enters the plenum through a carburetor or throttle body, then the individual pistons suck that air into the cylinders as need be.
Wet vs. Dry Flow
These terms refer to the manifolds intended application. A wet-flow manifold is one that carries both air and fuel, and a dry-flow manifold carries only air. Youll find wet-flow manifolds underpinning carbureted and throttle-body injected applications, which squirt fuel into the plenum. Multi-point fuel-injection systems typically use dry-flow manifolds, because they use fuel injectors to introduce fuel directly into the cylinder head instead of into the manifold. Dry-flow manifolds are generally more efficient, since engineers dont have to worry about the air and fuel separating around bends in the runners.
Runner and Plenum Size
Generally speaking, a smaller plenum and longer, narrower runners will enhance low-rpm torque; large plenums and short, fat runners bias more toward top-end horsepower. This works in part because the small plenum and longer runners force air to speed up as it travels to the cylinders, which fills the cylinders more quickly. However, those longer runners will ultimately limit airflow, which hinders absolute, high-rpm horsepower potential.
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