Assuming that the blower (Supply Air) and sucker (Exhaust) fans are roughly equivalent, and you have separate combustion-air ducting, you have a conventional balanced system.
If the fans provide combustion-air in addition to ventilation, you have a negatively pressurized system.
I prefer a slightly negative air pressure in the engine compartment
(relative to the living space); which will ensure that pollutants don’t migrate from engine rm. to cabin
See Caterpillar’s excellent paper on Engine Room Ventilation:
See also, some earlier discussions:
➥ Engine Ventilation: Skip it?
➥ Bilge/Motor Room Blower Exhaust Port?
➥ Engine ventilation