Performance Upgrades: Intake Manifolds

The intake manifold in a car feeds air into the cylinders for the purpose of combustion in an internal combustion engine. Due to space and cost limitations manufacturers fit plenums that are fed from one end while the other end is blocked. A plenum is an air chamber which distributes air to the cylinders. Ideally the plenum is supposed to equally distribute air flow to all the cylinders. In reality however this is not the case as the plenum only has as an air flow duct on one side. The cylinders near the duct get less air and the ones at the end get more as the air collects at the far end. 

The easiest solution is to fit a second throttle body to the far end of the plenum with a double air filter intake system. This only works on naturally aspirated engines as there is sufficient space to install another intake port. On turbocharged and supercharged engines there is no space for a second intake system. In this case, an aftermarket intake system or fit a different plenum has to be installed to stabilise airflow to all the cylinders. 

Keep the following factors in mind while going in for an after market intake manifold:

The plenum should increase in size rapidly before the intake for the first cylinder. 

The Plenum can taper towards the end after the first cylinder but at no point should it be less than half the size of the intake diameter of the intake runner. 

The Plenum should extend well beyond the last cylinder. 

The diameter and length of the intake manifold runner (the manifold that connects the cylinders to the engine) determines the power curve of an engine. The diameter of the intake runner influences the point at which the engine reaches peak power and the length of the intake runner influences the amount of power available at low or high RPM. 

A large intake diameter of the runner relative to the diameter of the intake valve will result in improved engine performance at high RPM but will compromise on power at low RPM. A longer intake runner will result in better low end torque at low RPM and a shorter intake runner will produce more torque at high RPM.

There are two types of modified intake system, short ram induction systems and cold air induction systems. Short ram induction systems generally consist of a short metal tube and a high flow air filter. Short ram induction systems pick up hot air from the engine bay and feed it into the engine via the air filter. Cold air induction systems has a longer metal tube that picks up colder ambient air from under the car’s grill and or from the front wheels arches. The intake for cold air induction systems is tricky as it cannot have too many bends and curves or airflow pressure will be lessened which is detrimental to increase in performance which is the whole point of a modified intake system. Another factor to be kept in mind for cold air induction systems is that the air filter should not be blocked by mud, slush, dirt or snow therefore the intake has to be placed in a way to avoid any of those chances. Make sure the air intake is not placed too low as it water can be sucked into the engine and cause hydraulic lock while driving through stagnant water.

Make sure you go to a well established and reputed modifying company or shop to install a performance intake system. These outlets have mechanics who are specifically trained to install these systems.