When the turbocharger in a car is not engaged, it does not mean that the engine is naturally aspirated. The turbocharger is typically connected to the engine's intake system, and its primary function is to increase the volume of compressed air entering the engine, thereby enhancing efficiency and power output.
When the turbocharger is not engaged, meaning it is in idle mode, the intake system will supply air to the engine through alternative paths. This may be achieved through the use of a valve controller or a valve switch. In the absence of turbocharger engagement, the engine relies on its own negative pressure to draw air into the combustion chamber.
Naturally aspirated refers to the engine's use of the movement of gases to increase the intake airflow. In certain engine types, the negative pressure generated from exhaust pulses in the exhaust pipe can assist in pushing fresh air into the combustion chamber. However, this process of naturally aspirated intake does not rely on the turbocharger and is a specific type of intake method.
Turbocharging and naturally aspirated are two distinct engine intake methods. Turbocharging enhances engine performance by increasing intake pressure, while naturally aspirated relies on the engine's operation to create negative pressure for air intake. These two technologies differ in terms of power output, fuel efficiency, and oil requirements.
In terms of power output characteristics, a naturally aspirated engine has smooth power delivery. In the low RPM range, its torque growth is modest, typically around 30 to 40 N·m. In comparison, a turbocharged engine exhibits a torque growth of approximately 70 N·m in the same RPM range, resulting in more robust acceleration but may also introduce a sudden surge.
Regarding fuel efficiency, turbocharged engines are more fuel-efficient than naturally aspirated engines. For example, compared to a 2.0L naturally aspirated engine, Volkswagen's 1.4TSI turbocharged engine achieves a similar power level while being more fuel-efficient.
Concerning oil requirements, naturally aspirated engines can use semi-synthetic or full synthetic oil, whereas turbocharged engines must use full synthetic oil with better wear and high-temperature resistance. To ensure the turbocharger remains undamaged, the use of full synthetic oil is necessary.
