Relative to ambient, what happens to MAP pressure when boost is diminished by a leak?

Relative to ambient, what happens to MAP pressure when boost is diminished by a leak?

• A. MAP pressure is lower than ambient
• B. MAP pressure is higher than ambient
• C. MAP pressure equals ambient pressure
• D. MAP pressure is unf affected by ambient

Answer: (A)

MAP is the absolute pressure inside the intake manifold. Boost is extra pressure above the outside air pressure (ambient). If a leak allows boost air to escape, that extra pressure can’t be maintained, so the manifold cannot stay pressurized above ambient. With the leak, the pressure in the manifold drops toward, or below, ambient levels as air leaks out. So relative to ambient, the MAP becomes lower than ambient. This is why a boost leak reduces manifold pressure instead of keeping it equal to or higher than the outside air.

MAP is the absolute pressure inside the intake manifold. Boost is extra pressure above the outside air pressure (ambient). If a leak allows boost air to escape, that extra pressure can’t be maintained, so the manifold cannot stay pressurized above ambient. With the leak, the pressure in the manifold drops toward, or below, ambient levels as air leaks out. So relative to ambient, the MAP becomes lower than ambient. This is why a boost leak reduces manifold pressure instead of keeping it equal to or higher than the outside air.