2025 Automotive Service Technician Complete Practice Test

The correct answer is based on the principle that atmospheric pressure is the primary force driving air into the induction system of a naturally aspirated engine. This type of engine does not use a supercharger or turbocharger; instead, it relies on the natural atmospheric pressure to draw air into the cylinders during the intake stroke.

As the piston moves down in the cylinder, it creates a vacuum, which allows atmospheric pressure to push air into the intake manifold and, subsequently, into the combustion chamber. This process is essential for the engine's operation because it combines the air with fuel for combustion.

In contrast, mechanical force from the crankshaft, while crucial for engine operation, does not directly drive air into the induction system. The Venturi effect, which is related to the reduction of pressure in a fluid flow, applies more specifically to carburetors and some fuel systems rather than the induction system of a commonly defined naturally aspirated engine. Fuel pressure plays a role in delivering fuel to the combustion chamber, but it does not influence the air flow directly in the same manner as atmospheric pressure does in an naturally aspirated engine. Overall, the correct answer highlights the reliance on atmospheric pressure as the driving force for air intake in this engine type.