Engine Manifold: A Quick Guide

The manifold is the area of the engine that provides the cylinders with fresh air. Working with the air intake, the throttle body, and the fuel distribution system to ensure that the engine burns the correct mixture of fuel and air.

The 2 main objectives of the fuel-injected engine are to retain a high volume of air and to distribute it evenly between each piston. In carbureted motors, the intake or inlet manifold shall transmit the fuel/air combination from the carburetor to the heads.

Components of An Inlet Manifold

Plenum Intake or inlet Manifold

The plenum is the major gap at the upper end of the manifold. It serves as, a storage keeping the air till it's up for it to pass through the cylinders. The plenum uniformly allocates the air to the runners before going through the inlet side.

The volume of the plenum influences the output of the motor. Aftermarket manifolds can have a divided plenum that can be split into 2. This configuration makes the centre of the manifold easily cleanable.

Inlet Manifold Runners

Runners are pipes that bring air from the plenum to the inlet pipe of each cylinder head. There are fuel injector terminals in each runner for fuel-injected motors. Fuel is pumped only before the air reaches the intake outlet.

The volume of the runner is a vital variable when it comes to engine efficiency. The length and width of the runners largely decide where the engine's maximum horsepower is.

How Does an Intake or Inlet Manifold Operate?

Air passes through the exhaust and the throttle area to the plenum of the intake manifold. Then the plenum diffuses the air evenly to each of the runners. During the injection process, the piston travels down and produces a low pressure within the piston. This pulls the air from the runner (high pressure area) into the piston.

As the intake valve shuts, it produces pressure changes that return the air to the runner. It then rebounds off the plenum and returns to the piston when the intake valve expands again.

This cycle happens over and over with each of the cylinders unless you shut down the engine.

Performance Inlet Manifolds

The configuration of the inlet manifold influences how much air is supplied and how fast it is. Anything from the width of the opening to the shape and size of the plenum and the runners will affect how and then when the air is distributed.

Performance inlet manifolds are fitted with larger plenums and improved airflow runners. Manifolds with a divided plenum make it easier to clean and scrub. Spacers may also be inserted to change the size of the plenum, which can allow you to achieve certain engine output curves.

A plenum tapered towards the final cylinder will allow more even distribution of air. Some manifolds often have an air space that actually reduces the build-up of heat for more fuel. Quality inlet manifolds are well combined with new exhaust, cylinder heads, cold air intake and throttle bodies.

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