Which statement best describes the effect of altitude on engine power?

• A. Higher altitude reduces air density, reducing engine power and overall performance.
• B. Higher altitude increases engine power due to cooler air.
• C. Altitude has no effect on engine power.
• D. Lower altitude reduces engine power due to thick air.

Answer: (C)

Engine power is governed by air density. As you climb, the air becomes thinner and less dense, so less mass of air enters the engine with each intake. That reduces the amount of oxygen available for combustion and lowers the energy produced, causing a drop in horsepower and overall performance, especially in normally aspirated engines. The idea that cooler air at altitude increases power is incorrect because, despite cooler temperatures, the drop in ambient pressure dominates and density remains lower than at sea level. Saying altitude has no effect on power isn’t accurate either, and the notion that lower altitude reduces power contradicts how denser air at lower levels actually helps engines produce more power.