intake system

The intake system draws atmospheric air into an internal combustion engine and meters it into the cylinders at the right pressure, temperature, and flow rate for combustion. It runs from the air filter through the intake manifold and terminates at the intake valve of each cylinder. Without it, the engine cannot breathe; a poorly tuned intake kills power and efficiency across the entire operating range.

A typical intake system consists of an air filter element (usually pleated paper or foam), an intake manifold (cast iron or aluminum), a throttle body that controls airflow volume, fuel injectors in port-fuel systems, and intake valves. In turbocharged or supercharged engines, a compressor sits upstream of the manifold and significantly raises intake air pressure and density. The manifold itself is designed to distribute air evenly to all cylinders; unequal lengths or cross-sections create uneven cylinder charging and power imbalance.

Two main configurations exist. In naturally aspirated engines, atmospheric pressure alone pushes air through the system; intake velocity and manifold resonance help fill cylinders near full load. Boosted engines use a turbocharger or supercharger to force air in under pressure, typically 0.5 to 2 bar gauge depending on application and engine durability limits. Intercoolers sit between the compressor and intake manifold in turbocharged designs to cool the compressed air, restoring density lost to heating.

Common problems and tuning

Restricted air filters choke airflow and reduce power; excessive restriction triggers the check engine light via a pressure sensor. Carbon deposits on intake valves and injectors reduce flow and cause rough idle, particularly in direct-injection engines. Vacuum leaks between the intake manifold and cylinder head allow unmetered air past the throttle, causing lean-running and stumbling. Manifold cracks are difficult to diagnose but create similar symptoms.

Intake design affects power across the rev range. Longer manifold runners favour low-rpm torque by allowing air column inertia to pack cylinders more fully; shorter runners improve high-rpm power. Variable intake manifolds and tuned runner lengths are now common on performance engines. Acoustic resonance at certain engine speeds can reinforce cylinder filling; manufacturers exploit this with variable geometry or tuning the manifold shape to match target operating points.