What is the effect of higher density altitude on engine performance?

• A. Engine performance decreases.
• B. Engine performance increases.
• C. No change.
• D. Only turbocharged engines affected.

Answer: (A)

As density altitude increases, the air becomes thinner, so less air mass is drawn into the engine during each intake cycle. Since engine power is largely determined by how much air (and therefore oxygen) can be burned with fuel, thinner air means less combustion energy and thus less power. This decrease happens for normally aspirated engines and is only partially offset in turbocharged engines by increasing boost, but not enough to prevent a net loss of performance at higher density altitudes. So, overall engine performance decreases with higher density altitude.