A twin-turbo system uses two turbochargers to force extra air into an engine so it can burn more fuel and make more power. In a V6 or V8 engine, each turbo is often fed by exhaust from one bank of cylinders. This matters because an engine is basically an air pump, and more compressed air can mean stronger combustion.
Twin turbos can improve power without requiring a much larger engine.
Key Facts
- A turbocharger uses exhaust energy to spin a turbine connected to a compressor.
- Boost pressure is the extra intake pressure above atmospheric pressure, often measured in psi or bar.
- More air plus the correct amount of fuel produces more engine torque and power.
- Power = torque x angular speed, or P = τω.
- Pressure ratio = absolute outlet pressure / absolute inlet pressure.
- An intercooler cools compressed air so it becomes denser before entering the cylinders.
Vocabulary
- Turbocharger
- A device that uses exhaust gas to spin a compressor that pushes more air into an engine.
- Boost
- Boost is the amount of intake air pressure added by a turbocharger above normal atmospheric pressure.
- Intercooler
- An intercooler is a heat exchanger that cools compressed intake air before it enters the engine.
- Turbine
- The turbine is the exhaust-driven wheel in a turbocharger that extracts energy from hot exhaust gases.
- Compressor
- The compressor is the intake-side wheel that squeezes air to a higher pressure before it flows to the engine.
Common Mistakes to Avoid
- Thinking the turbo is powered by a belt, which is wrong because a turbocharger is driven by exhaust gas rather than directly by the crankshaft.
- Ignoring the intercooler, which is wrong because compressing air heats it and hot air is less dense and more likely to cause knock.
- Assuming twin turbos always double the power, which is wrong because power also depends on engine strength, fuel delivery, tuning, airflow limits, and heat control.
- Confusing parallel and sequential twin-turbo layouts, which is wrong because parallel systems often split exhaust flow between two turbos while sequential systems use turbo timing to improve response across different engine speeds.
Practice Questions
- 1 A twin-turbo engine makes 400 N m of torque at 5000 rpm. Use P = τω and ω = 2π rpm / 60 to find the power in watts and kilowatts.
- 2 A turbo system takes in air at 100 kPa absolute pressure and compresses it to 180 kPa absolute pressure. What is the pressure ratio?
- 3 Explain why cooling the air after the turbocharger can increase power and protect the engine, even though the air has already been compressed.