Intake
From Wikipedia, the free encyclopedia
An intake is an air intake for an engine. Because the modern internal combustion engine is in essence a powerful air pump, like the exhaust system on an engine, the intake must be carefully engineered and tuned to provide the greatest efficiency and power. An ideal intake system should increase the velocity of the air until it travels in to the combustion chamber, while minimizing turbulence and restriction of flow. This is usually accomplished by flow testing on a flow bench in the port design stage. Cars with turbochargers or superchargers which provide a pressurized intake system, usually have extensive tweaking of the intake system to improve performance dramatically.
A modern air intake system should have three main parts, an air filter, mass flow sensor, and throttle body. Many cars today now include a silencer to minimize the noise entering the cabin. Silencers impede air flow and create turbulence which reduce total power, so many performance enthusiasts often remove them.
Production cars have specific length air intakes to cause the air to vibrate and buffett at a specific frequency to assist air flow in to the combustion chamber. Aftermarket companies for cars have introduced larger throttle bodies and air filters to decrease restriction of flow at the cost of changing the harmonics of the air intake for a small net increase in power or torque.
BMW is unusual in that its M line of performance cars have one throttle body per cylinder, as opposed to one throttle body for four, six or even eight cylinders for regular production cars. This is done to increase flow characteristics and improve throttle response. Nissan also uses this system in their high performance models.
Porsche in the 1980s designed an intake system for their cars that changed the length of the intake system by alternating between a longer and shorter set of tubing using a butterfly valve, creating a small amount of positive pressure which increased overall performance of the engine.
Alfa Romeo used variable-length intake in their 2.0 Twin Spark engines powering the model 156.
