What Is an Intake Manifold in a Car & What Does It Do?

Educational

Mar 05th, 2020

What Is an Intake Manifold in a Car & What Does It Do?

For your car to move, it needs (among many things) not only fuel but also oxygen. These ingredients feed the engine to set off a complex process called internal combustion or the combustion cycle. 

Without going into the details of the combustion cycle, we understand that it's a process that causes a series of explosions in the combustion chamber of an engine. These explosions are responsible for rotating the crankshaft and providing the mechanical force necessary to set a vehicle in motion.

In this article, we will look into the intake manifold and see how and where it figures in the process we just described.

The oxygen needed by a car's engine comes from the surrounding air. Oxygen constitutes approximately 20% of the air we breathe, and it is the function of the air intake system to ‘take in’ and guide air through the intake manifold and into the combustion chamber to ensure that internal combustion takes place correctly. 

What is an Intake Manifold?

Let’s take a closer look at this series of tubes. The intake manifold (aka inlet manifold), which is the last stop of the air before entering the cylinder heads, sits atop the engine. It comprises of moulded plastic or metal tubes that divide the air equally to ensure proper mixing with the fuel. Its work is crucial for the efficient and even distribution of air in the cylinders. 

Before air is allowed into the combustion chamber and as it passes through the intake manifold, various sensors scrutinise its temperature, pressure, and composition. Analysing these factors is the work of the sensors, while controlling the amount of air that goes into the engine is the function of the throttle body. The inlet manifold works in harmony with all these auto parts. Together they ensure that there is proper air-fuel ratio before the camshaft opens the cylinder valves for combustion to take place. 

What Does an Intake Manifold Do?

The intake manifold has two components, and these are the plenum and the runners. The plenum is the large cavity at the top of the intake manifold, while the runners are the small tubes that run to the cylinders. The intake manifold also holds the throttle valves and has several separate sections in large engines. Here are its functions:

1. Acts as a channel that supplies the combustion chamber with air

Looking at the bigger picture, let’s see how air from outside gets to the inlet manifold. 

The air intake system draws air from around the car. The air passes through the air filter, travels in the intake boot, and reaches the throttle body. The throttle acts like a sentinel that regulates the air that will be allowed to flow through. From there, the let-through air enters the plenum, goes through the runners, and into the cylinder head. 

2. Provides the turbulence needed to improve fuel efficiency

While it looks like transferring air (or air-fuel mixture in carburetted engines) from one place to another is all that an intake manifold does, it’s not. The design of the intake manifold involves precise engineering. 

Rough surfaces in the intake create short-lived turbulence which aids in more efficient burning of fuel. This does not only contribute to fuel economy but also helps reduce engine knock. 

3. Contributes to volumetric efficiency

The width of the inlet ports and how the contours taper jointly affect the engine’s volumetric efficiency (VE). Higher VE means more air available in the cylinder, which translates into more engine torque. In other words, torque is maximum when VE is maximum. 

Generally, the design of the intake manifold depends on the engine speed and load capacity. It is worth noting that the route of the air to the cylinder head increases or decreases the engine's efficiency and overall performance.

We will publish a more in-depth article to explain the concepts of turbulence and volumetric efficiency in vehicles. For now, we hope you gained a working knowledge of how an intake manifold affects the workings of an engine. 

Intake Manifold Problems That You Should Know

Like in any other part of your car, intake manifold issues can undermine the performance of your vehicle’s engine. 

1. Cracks 

Cracks in the intake manifold gasket can cause leaks and improperly-pressurised air. 

2. Vacuum, Coolant, or Oil Leakages

Vacuum, coolant, or oil leakages can disturb the proper functioning of the intake manifold. Mostly, the Check Engine light turns on if there is an issue in the intake manifold. 

3. Carbon Build-Up

Carbon build-up in the intake manifold restricts airflow and can cause power loss, fuel inefficiency, and misfiring. Turbocharged engines are more prone to this issue. 

If you notice any of these things happening, immediately arrange for a checkup, repair or replacement of the intake manifold or its gasket. Always buy replacements from a reliable car parts dealer and choose the one that fits your car’s make and model. 

While you’re at it, please check out Carpart.com.au. It is a quicker and easier way to shop for car spare parts. You may send your requests for car parts to this online platform or search its classifieds section for aftermarket, OEM, used or new auto parts.