Inlet manifold

The intake manifold has historically been manufactured from aluminium or cast iron, but use of composite plastic materials is gaining popularity (e.g. most Chrysler 4-cylinders, Ford Zetec 2.0, Duratec 2.0 and 2.3, and GM's Ecotec series).

Better atomization allows for a more complete burn of all the fuel and helps reduce engine knock by enlarging the flame front.

This process occurs at the speed of sound, and in most manifolds travels up and down the runner many times before the valve opens again.

The traditional solution has been to tune the length of the intake runner for a specific engine speed where maximum performance is desired.

However, modern technology has given rise to a number of solutions involving electronically controlled valve timing (for example Valvetronic), and dynamic intake geometry (see below).

The exhaust manifolds achieve a vacuum in the cylinder just before the piston reaches top dead center.

[citation needed] The opening inlet valve can then—at typical compression ratios—fill 10% of the cylinder before beginning downward travel.

[citation needed] Instead of achieving higher pressure in the cylinder, the inlet valve can stay open after the piston reaches bottom dead center while the air still flows in.

This minimizes interference of one cylinder's pressure waves with those of another, giving better torque from smooth mid-range flow.

Such manifolds may have been originally designed for either two- or four-barrel carburetors, but now are used with both throttle-body and multi-point fuel injection.

An example of the latter is the Honda J engine which converts to a single plane manifold around 3500 rpm for greater peak flow and horsepower.

First, two discrete intake runners with different length are employed, and a butterfly valve can close the short path.

As the name implies, VLIM can vary the length of the intake tract in order to optimize power and torque, as well as provide better fuel efficiency.

There are two main effects of variable intake geometry: Many automobile manufacturers use similar technology with different names.

Carburetors used as intake runners
A cutaway view of the intake of the original Fordson tractor (including the intake manifold, vaporizer , carburetor , and fuel lines)
Comparison of a stock intake manifold for a Volkswagen 1.8T engine (top) to a custom-built one used in competition (bottom). In the custom-built manifold, the runners to the intake ports on the cylinder head are much wider and more gently tapered. This difference improves the volumetric efficiency of the engine's fuel/air intake.
Lower intake manifold on a 1999 Mazda Miata engine , showing components of a variable length intake system.