Typical volumetric efficiency range of a well-designed naturally aspirated engine For a healthy, well-designed naturally aspirated engine at its best operating region, which range best represents the volumetric efficiency?

Introduction / Context:
Volumetric efficiency quantifies how effectively an engine breathes: the actual mass of air inducted compared with the theoretical mass that would fill the displacement at ambient conditions. It strongly influences torque, power, and fuel economy.

Given Data / Assumptions:

• Naturally aspirated four-stroke engine without boost.
• Operation near peak torque where intake tuning is favorable.
• Standard atmospheric conditions and proper air filtration.

Concept / Approach:
VE depends on intake/exhaust tuning, valve timing, port geometry, and engine speed. Well-optimized naturally aspirated engines often achieve 0.80–0.90 VE (80–90%) at their best point; some tuned racing engines can briefly exceed 100% due to dynamic ram effects, but for general engineering estimates, the 75–90% range is the accepted textbook band.

Step-by-Step Solution:
Define VE = actual air mass inducted / theoretical mass at ambient density.Consider tuned operation: favorable pressure waves raise cylinder filling.Typical NA street/industrial engines: VE commonly 0.75–0.90 at the sweet spot → choose 75–90%.

Verification / Alternative check:
Dyno airflow measurements and engine simulation outputs for well-designed NA engines consistently indicate VE in this band at peak torque.

Why Other Options Are Wrong:
30–70% would describe severely restricted or off-design operation. Modern engines generally exceed 70% VE under favorable conditions.

Common Pitfalls:
Assuming VE is constant across the speed range; it varies significantly with RPM and valve timing.

Final Answer:
75 to 90%