My gasoline engine
boat has both.
The factory installed the blowers sucking from the lowest point below each engine.
One of my modifications was to add thermostatically-controlled blowers sucking from above the
fuel rail. This was my 100% effective solution to eliminate heat-soak vapor lock that would prevent restart after dropping
anchor for an hour in tropic temperature
water / air
environment.
The only issue is if both engines are running (drawing air), the OEM blowers are running and my heat
exhaust are all running at the same time, then my
hull will implode like an egg shell.