How does the intake manifold work?

Evolution of Intake Manifolds
Prior to 1990, many vehicles had carburetor engines. In these vehicles, fuel is dispersed inside the intake manifold from the carburetor. Therefore, the intake manifold is responsible for delivering the fuel and air mixture to each cylinder.

To prevent the fuel from condensing on the cold walls of the intake manifold, heating is required. This can come from electric heating in the manifold, exhaust gases passing underneath, or from coolant circulating around it. Most intake manifolds from this time are made of cast iron or cast aluminum.

Starting in the early ‘90s, the majority of engines began using fuel injection to deliver gas to the cylinders. In these engines, the intake manifold is only involved in air distribution. Since heat is no longer needed to prevent fuel condensation, other materials can be used. It’s common to see cast aluminum as well as plastic intake manifolds on modern vehicles.


How to Work?
The intake manifold, also known known as the inlet manifold, distributes air to the engine’s cylinders, and on many cars it also holds the fuel injectors. On older cars without fuel injection or with throttle body injection, the manifold takes in the fuel-air mixture from the carburetor/throttle body, to the cylinder heads.

The manifold lets air into the combustion chamber on the intake stroke, and this air is then mixed with fuel from the injector, after which the combustion cycle continues.

The air reaches the manifold through the air cleaner assembly, which contains the car's air filter.

The air filter stops dust and other foreign bodies from entering and damaging the engine, so it's vital that you regularly change it.


The plenum is the large cavity at the top of the manifold. It acts as a reservoir, holding the air until it’s ready to go into the cylinders. The plenum evenly distributes the air to the runners before it passes through the intake valve.
The size of the plenum impacts the engine’s performance. Aftermarket manifolds can have a split plenum that can be separated into two. This design makes it easier to clean the inside of the manifold.
The runners are tubes that carry air from the plenum to the intake port on each cylinder head. For fuel-injected engines, there are ports for the fuel injectors in each runner. Fuel is injected just before the air goes into the intake port.
The size of the runners is a critical factor when it comes to engine performance. The width and the length of the runners largely determine where the peak horsepower of the engine is.


Performance Intake Manifolds
The design of the intake manifold affects how much air is delivered and how quickly. Everything from the diameter of the openings to the size and shape of the plenum and runners can alter how and when air is delivered.

Performance intake manifolds are equipped with larger plenums and runners for better airflow. Manifolds with a split plenum allow for easier polishing and cleaning. Spacers can sometimes be added to adjust the plenum size, which can help you obtain certain engine performance curves.

A plenum that is tapered toward the final cylinder will ensure more even air distribution. Some manifolds also have an air gap that helps reduce heat buildup for more power. Performance intake manifolds pair well with a new exhaust, cold air intake, cylinder heads, and throttle bodies.


All right, now we look what are the symptoms of a bad intake manifold?
The answer is :While idling, there may be a hissing, whistling, sucking, gulping or even slurping noise. The car may also feel rough while idling and the engine may even stall completely at slow speeds. Or, when you turn off the car's ignition, it may keep on running for a while longer than it should. It could also feel sluggish when accelerating.
If you have the problem as above,so go to the garage and check,maybe you need change a new intake manifold.

Post time: Dec-30-2022