The VE for a stock two-valve, four-stroke engine is 95%.

• A. False
• B. True
• C. Depends on RPM
• D. Cannot be determined

Answer: (A)

Volumetric efficiency measures how effectively the cylinder is filled with air compared to the ideal fill at the same pressure. In a stock two-valve, four-stroke engine, air has to travel through restrictive intake ports, valve openings, and the throttle, and timing effects can cause pressure losses. These factors keep filling below the ideal 100% and make VE vary with engine speed, cam timing, and other operating conditions. Because VE isn’t a fixed value and can change across RPM ranges—and it’s not guaranteed to sit at a specific number like 95%—stating that the VE is 95% for a stock setup isn’t generally correct. It can approach that value in some conditions, but it’s not universal.