Intake Manifold Runner Control

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The intake manifold runner control (IMRC) is a valve that controls the ratio of air to gas in a car. This article provides information regarding the same.
WheelZine Staff
Last Updated: Jun 3, 2018
Using a car is today's necessity. But, we cannot keep on driving a car without considering its performance. In today's time with the increasing gas prices and economic recession still hovering about each one's head, its performance is a really important issue. It depends on many factors such as the area through which one is passing, time of the day, and the way one drives. The mileage per gallon basically depends on how efficiently the fuel is burned in the engine to produce the thrust, or the force to propel the car forward.


The valve serves as an enclosure, wherein tiny droplets of the fuel mixes with the cold air to form the combustion mixture. Its prime responsibility is to transport the combustion mixture to each intake port on the cylinder head. It has to perform this task of even and optimal distribution of the combustion mixture to each cylinder of the engine to ensure high performance. In modern cars, the intake manifold runs tubes or runners from its central enclosure or plenum, so that it can supply combustion mixture to each cylinder of the engine individually. In practice, its runner control assemblies are located between this valve and the cylinder head of the engine.

While supplying fuel to an engine, it is of utmost importance to maintain the percentage of air and fuel in the mixture at 14.7:1 ( air to fuel ). In case of fuel injection engines, the intake manifold conveys only air to the cylinders at the fuel injector ports, where it is mixed with the fuel. The combustion mixture flows through the runner to the cylinder, and when it hits the closed intake valve on it, it creates shock wave and heat. This shock wave travels inside the manifold back and forth at the speed of sound. Since the cold air has a higher density than hot air, it is breathed in from the atmosphere. The fuel which is mixed with it expands more and delivers more thrust when ignited.

To achieve high-engine performance it is necessary to time the opening of the intake valve on the cylinder to the peak of the shock wave. The opening of the valve depends on the speed of the engine running at, and the shock wave timing depends on the length of the runner and speed of the sound. In traditional engines, the length of the runner is matched to a particular engine speed range within which, it is hoped to deliver maximum performance. Any value above and below this range does not ensure maximum car performance.

However, this is not the case in modern engines, wherein a computer watches over the performance of the car parts and takes corrective steps to maximize it. The car's on-board computer can do so, by electronically controlling the timing of the opening and closing of the intake valve as well as advanced intake geometry. In modern cars, variable length intake manifolds are used to provide maximum fuel efficiency at low and high engine speeds by optimizing the power and torque produced by the engine.

Variable Runner Controls

Each cylinder of the engine is serviced by two runners of unequal length, connected to each of the intake parts in the cylinder hands. One of these is always open. Depending on the workload on the engine, other runners are opened or closed with the help of a butterfly valve or a valve plate, and the flow of combustion mixture is controlled and matched to the demand of the engine. This is a butterfly valve. The cylinders in an engine running at a speed below 3,000 rpm is serviced by the runner that is always open. When the driver of the car steps on the gas pedal, and the engine's rpm crosses 3,000-3,400 rpm range, the other runner is opened with the help of a valve to meet the increased demands of air and gas. This secondary runner opens and closes when the powertrain control module activates a motor that makes the valve move. The driver of the car can actually hear it open up. All this arrangement improves the high-speed engine performance to get as high a gas mileage as possible.

All in all, keeping the runner control open makes the car lose on fuel efficiency, and you pay much more for traveling at low speed because the car is using the fuel at the setting for high speed. However, when you floor the gas pedal to travel at a high speed, you start paying right. If you find your car's mileage slipping below the normal level, then there are high chances that something's wrong with the gasket or the runner control.