ICE-15 — Turbocharging

ASSUMPTION — Boost values vary by engine and application; exact values must be verified from OEM data.

In this lesson you will learn:

• The working principle
• Turbocharger vs supercharger
• Turbo lag

1. Working Principle

A turbocharger uses exhaust-gas energy to compress intake air (forced induction).

FACT — Exhaust gas spins a turbine; the turbine drives a compressor on the same shaft, which compresses intake air. Volumetric efficiency rises above 1, giving high power from a small displacement.

2. Turbocharger vs Supercharger

• Turbocharger — driven by exhaust gas; “free” energy but lag.
• Supercharger — driven mechanically by the crankshaft; instant response but parasitic power.

FACT — The turbo recovers exhaust energy (efficient) but lags at low RPM; the supercharger responds instantly but consumes engine power.

3. Turbo Lag

Turbo lag is the delay in building boost after the throttle opens.

FACT — Lag comes from the time needed to spin up the turbine-compressor. A small turbo has less lag but lower peak flow; a large turbo the opposite. Variable-geometry turbo (VGT) and twin/sequential turbos soften this trade-off.

4. Boost Control

FACT — Boost is controlled by a wastegate (or VGT vanes) that routes exhaust around the turbine. The ECU manages it to prevent overboost and knock.

5. Summary

• Turbo compresses intake air with exhaust energy.
• Supercharger is mechanically driven; instant but parasitic.
• Lag is the spin-up delay; boost is controlled via wastegate/VGT.

6. Sources

• Heywood, Internal Combustion Engine Fundamentals
• Bosch Automotive Handbook

Next Lesson

• ICE-16 — Intercooling: cooling the compressed charge.