Ram Air Effects on the Air Side Cooling System Performance of a Typical North American Passenger Car

A standard engine mounted cooling fan in a 1976 Ford Granada equipped with air conditioning and a 4.9ℓ (302 cu. in.) V-8 engine was performance-tested on the road and under wind tunnel generated ram air conditions. To achieve appropriate back pressure variation the whole engine bay was pressurized through use of remotely placed plant exhauster machinery.

System resistance was studied over a range of ram air conditions, and was shown to be composed of a ram air loss, a stationary vehicle front end loss, an engine bay blockage loss, and the radiator cooling air dynamic pressure, or face head. Ram air and cooling air flow caused engine bay pressure to be slightly positive relative to the ambient static pressure level.

Fan pressure-flow characteristics were measured for various fan speeds and three ram conditions. These were observed to correlate as one universal map. This universal characteristic together with the measured front end resistances and ram pressure was interpreted as series-operated fans consisting of a supercharging first stage and the cooling fan acting as a second stage. This model and the identified resistance mechanisms enables accurate performance prediction to be made.