Simply put, an intake manifold (also called inlet manifold) distributes air to the cylinders of an engine. It works together with the air intake, throttle body, and fuel delivery system to ensure that the engine is burning the right amount of both air and fuel. Basically, an intake manifold is a liaison between a car’s throttle body and its cylinders. For fuel-injection engines, the intake manifold is responsible for maintaining a high volume of air and distributing it evenly across the cylinders. For carbureted engines, the intake manifold supplies the fuel/air mixture from the carburetor to the cylinder heads.
That being said, an intake manifold is more than just the connector between a carburetor or throttle body to the ports in the cylinder head. It is a fundamental part of a vehicle’s induction system that must match the airflow characteristics of the cylinder head and camshaft, in addition to the engine’s displacement and RPM range. A well-designed intake manifold that is properly matched to your specific engine’s requirements will, therefore, produce more horsepower and torque than one that is not.
Image each cylinder in your car’s engine as a member of the same team working together toward the same goal. The mission is to produce the maximum amount of power with each one putting in the same amount of effort. When this takes place, the engine runs stronger, smoother, and more reliably than before. If one or more of the cylinders slack off, the engine will noticeably run rougher, deliver less power, and be more prone to failure. The intake manifold acts in a managerial role to make sure everyone is doing their job and that the team starts and finishes on time.
What Is the Intake Manifold’s Job?
You need air to breathe and so does your car. Just as oxygen is crucial to sustaining life for a living being, it is also an integral part of your car’s internal system. What makes movement possible in cars that have internal combustion engines is a series of tiny explosions that take place within the combustion chambers. The fuel for these explosions is gasoline, but they would not be able to take place without being combined with oxygen. In conclusion, there has to be an appropriate amount of air and fuel in your vehicle’s cylinders for any action to take place.
This is where an intake (or inlet) manifold comes in. If we are still going off of the body metaphor, then an intake manifold is the lungs and the engine is the heart. The intake manifold consists of a series of tubes that evenly distribute the air that comes into the engine to each of the cylinders (however many that may be). This is done to ensure that the right amount of air can mix evenly with the right amount of fuel.
Most internal combustion engines use a four-stroke process: intake, compression, combustion, and exhaust. During the first stroke, air from the intake manifold travels to each cylinder through a valve. The intake valve then closes and the air-fuel mixture is sealed inside the cylinder before the other three strokes in the process occur. It reopens when the cycle begins all over again. It is the intake manifold’s responsibility to ensure that there is enough air available when the valve opens for each stroke to take place. Its job also includes making sure that every individual cylinder gets the same amount of air as the others.
Parts of an Intake Manifold
An intake manifold has three parts: the plenum, the runners, and the gasket.
Intake Manifold Plenum
The intake manifold directs the air and fuel mixture from the throttle body to the plenum. The intake manifold plenum (air enclosure/chamber) is a large cavity located at the top of the manifold. It acts as a reservoir, housing the air until it is ready to be sent into the cylinders. The plenum facilitates the even distribution of the air and fuel mixture to the runners before it passes through the intake valve. This distribution optimizes engine efficiency and performance. Additionally, the shape and size (volume) of the intake manifold plenum is a major consideration.
- Single-Plane Intake Manifold: On a single-plane intake manifold, all of the runners directly connect to a single common plenum with minimum bends to reduce airflow restriction. This type of manifold houses a large, open plenum that feeds all eight cylinders through shorter runners. The open, free-flowing design, however, reduces airflow velocity at lower RPMs. Single-plane manifolds, therefore, work best with high-RPM race engines because they tend to make the best power between 3,000 and 8,000 RPMs.
- Dual-Plane Intake Manifold: A dual-plane intake manifold is divided into two plenums that each feed four cylinders through slightly longer runners. This type of manifold houses a smaller plenum that increases the airflow velocity producing better power off idle and at cruising RPMs. Low RPMs means improved acceleration from a standstill. Dual-plane manifolds make the best power between idling and 6,000 RPMs and are ideal for vehicles that are used mostly for street driving.
Intake Manifold Runners
The Intake manifold runner is a series of tubes that channels intake air from the plenum to the intake ports. They are connected to the plenum individually and extend to the cylinder head intake ports. The job of the runners is to evenly distribute the air to the engine’s cylinders. The length and diameter of the runners impact the power curve of the engine. The diameter influences the point at which peak horsepower is reached, while the length affects the amount of power available across the RPM range.
- Variable-Length Intake Manifolds: Variable-length intake manifolds have specially tuned runners designed to deliver more power across a wider RPM range. With a fixed-length runner, you can only experience a performance boost within a narrow RPM band. For this reason, many aftermarket performance intake manifolds come with variable-length runners. These manifolds boast a combination of different sized runners to give you a broader power range for optimal performance. Some even include butterfly valves that open and close depending on engine speeds. At high RPMs, the valve opens to redirect air on a shorter path. Short runners with a wider path are ideal for higher RPMs because they allow for enhanced airflow and less restriction. At low RPMs, the valve will close to transmit air through a longer path. Narrow runners are great for low RPM ranges because they increase velocity and turbulence for improved combustion.
Intake Manifold Gasket
The intake manifold gasket seals the holes between the inlet manifold and the intake valves on the cylinders. The role of the gaskets is to seal the intake manifold against the cylinder heads. It provides a reliable and vibration-proof means of connecting the two components without leaks. In addition to sealing the engine vacuum, certain gasket designs can also seal engine coolant. If the intake manifold gasket is experiencing a problem, it can cause drivability issues and sometimes even engine overheating. A faulty gasket will give off certain symptoms, however, that can help alert the driver of these potential issues such as misfires, overheating, and coolant leaks.
Shop All Intake Manifolds Here
Some of our popular intake manifold brands:
