Intake Manifolds

How evenly does the air reach each cylinder, and how freely does the throttle let it through? In this category we bring together intake manifolds, plenums, throttle bodies and spacers for you who want to change the airflow in your project or replace an original part with a different design.

What do the intake parts do?

The intake manifold distributes the air from the throttle body to the cylinders. Runner length, runner diameter and plenum volume typically affect the rev range in which the engine pulls best. From Skunk2 Racing, for example, you will find manifolds and plenums with centre or side feed, and the position of the inlet can affect the distribution between the cylinders. The throttle body regulates the amount of air, and aFe, for example, offers throttle bodies from 76 to 90 mm. Throttle or manifold spacers can affect the airflow and, depending on the material, reduce heat transfer from the engine. Other brands in the category include Edelbrock, Wehrli and S&S Cycle.

How to choose a manifold and throttle body

Consider several factors together – size alone does not determine performance:

• Rev range: longer runners can typically strengthen pull lower down, while shorter runners and a larger plenum often move performance higher up the rev range.
• Throttle diameter: it must match the manifold, hoses and the engine's air demand; an oversized throttle can give less precise throttle response.
• Engine management: a changed air volume may require adjustment of the engine management and possibly of the fuel injection.
• Boost pressure: on engines with a turbo or supercharger, the manifold and gaskets must be able to withstand the pressure.
• Space: check the clearance to the bonnet, hoses and wiring.

Installation and maintenance

Fitment depends on engine code, model year and other modifications, so always compare the product description with your engine. Use new gaskets, tighten to the specified torque and check for vacuum leaks after installation, as leaks can cause a rough idle. Clean deposits from the throttle at regular intervals. For a complete intake setup, you can combine with air intakes and airboxes.

Frequently asked questions

Does a larger throttle body require engine management tuning?

It depends on the car and the engine management. Some engines adapt by themselves within certain limits, while others may get a rough idle or fault codes without tuning. Check the product description and plan for any calibration.

What is the difference between a centre-feed and a side-feed plenum?

The difference is where the air enters the plenum. The position can affect how evenly the air is distributed between the cylinders and how the part fits in the engine bay. The choice depends on the engine, the space available and the rest of the intake.

Can I drive on the road with a modified intake manifold or a different throttle body?

It depends on the product and the car. Changes to the intake can affect emissions and may need to be approved at inspection. Check the approval for the specific part number before fitting the part to a registered car.

Why does the engine run unevenly after installation?

This is often caused by a vacuum leak from a leaking gasket or hose, or by the engine management not being adapted to the new air volume. Check seals and tightening, and read out any fault codes.