Turbocharger systems are used to increase the horsepower output of an engine. However, a turbo system can also help an engine achieve better fuel economy compared to a non-turbo counterpart. There is no universal rule as to which setup will produce the greatest fuel economy in different vehicles and engines. Knowing how a turbo system functions will help you understand the ways that turbocharging affects fuel economy.
Turbochargers are composed of two separate turbine wheels connected by a metal shaft. The turbines are built into a metal turbo housing that directs airflow through each turbine and out the other end of the turbocharger unit. When the engine is accelerated, exhaust gasses are routed through one of the turbine wheels. This causes the turbine to rotate, commonly referred to as spooling. Since the turbines are connected by a shaft, the intake turbine wheel spins along with the exhaust turbine wheel. The intake turbine will therefore pull air in from the atmosphere and pressurize it before it is routed into the engine intake. This substantially increases the engine's airflow potential.
Turbo Fuel Consumption
Since a turbo system forces pressurized air into the engine, the engine will be able to burn much more air and fuel than a comparable non-turbo engine. This is especially beneficial in low displacement engines, which are generally incapable of producing very much low end horsepower. This allows a low displacement engine to perform at the level of much larger displacement engines. As such, a turbocharged engine can offer the performance benefits of a larger engine, while offering the fuel economy of a low displacement engine in situations such as highway cruising, in which the turbocharger is not spooled.
Non-Turbo Fuel Consumption
Non-turbo engines lack the horsepower potential of comparable turbocharged engines. However, this does not necessarily increase the potential for higher fuel economy. Since non-turbo engines are incapable of producing the substantial low-end horsepower that turbocharged engines produced, non-turbo engines often feature shorter transmission gear ratios to compensate for the lack of horsepower. Shorter gear ratios will make the engine run at a higher average rotations per minute (RPM). The increased engine revolutions needed to produce adequate power can cause a non-turbo engine to experience lower fuel economy, especially at cruising speeds.
Some of the most fuel efficient production engines are turbocharged diesel engines. Turbodiesel engines are capable of safely running a much higher turbocharger pressure setting. This allows a turbodiesel engine to produce a substantial low-rpm torque output. For that reason, turbodiesel engines can be driven in most situations at a much lower RPM than other engines, which helps them achieve a very high level of fuel economy.
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