What is the numeric value of the optimal throttle capacity expressed in RPM?

• A. 1800
• B. 1200
• C. 3200
• D. 2400

Answer: (D)

The idea being tested is finding the operating point where throttle capacity and engine speed give the best balance of air flow, torque, and efficiency for the given load. The optimal throttle capacity expressed in RPM is the speed where the engine can draw in enough air to meet the demand without wasting fuel or incurring excessive pumping losses, staying within the efficient portion of the torque and fuel maps. At mid-range speeds, like 2400 RPM, the engine typically has good volumetric efficiency and a favorable air–fuel combination, so the throttle can supply what’s needed without overshooting or under-supplying air. Lower speeds don’t provide enough air for the required torque, while higher speeds push the engine toward less efficient regions where additional throttle input yields diminishing gains. Therefore, 2400 RPM is the best balance point for optimal throttle capacity.