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Old 07-23-2008, 10:40 PM   #1 (permalink)
EcoModding Lurker
Join Date: Jul 2008
Location: California
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Moving air intake into the engine compartment?

On most unmodified cars air enters from the front both through the engine air intake located above the radiator, and through the radiator itself. At highway speeds a lot of air blows through the grills, through the radiator, and then exits into the wheel wheels or under the car, and of course the air from the engine intake eventually goes out the exhaust. Once we start blocking the front grills less air will be available to be pushed through the radiator, and the engine air intake location may no longer be in or next to the primary air flow into the car.

Hypothetically, once the grills are blocked, would there be an advantage to moving the air intake into the engine compartment behind the radiator somewhere?

We can estimate how much air the motor moves. For a four stroke 2 liter motor at 3000 rpm, there will be one intake stroke per cylinder every other rotation, so total engine intake volume is 1500 * 2 = 3000 liters/minute (or 106 cubic feet per minute). That's an upper limit, since the EGR valve will feed exhaust back in, some percentage of this will not be from the air intake. (It's remarkable how little air passes through a small car motor, typical pedestal fans like one finds around the house move thousands of CFM.)

I have no idea what the air flow through a radiator is typically on the highway. Radiator fans tend to be rated at 1000-3000 CFM, but that is most likely a free air rating, so it doesn't really tell us how much air these actually drag through a radiator.

Anyway, if the air intake is placed in the engine compartment it will tend to drop the pressure in there, which will tend to draw more air through the radiator from whatever grill openings remain. Better still, the radiator air consumed by the motor doesn't have to exit the engine compartment in the normal manner, instead it will be blown out the exhaust.

There are some problems that could arise. The intake air will be considerably warmer than the car was designed for. Some "cold air intakes" are inside the engine compartment, but these are usually employed with a normal front grill. The motor isn't going to be damaged by the hotter intake air, but the MAF sensor might have issues. The inside of the engine compartment tends to be oily, which would foul the air filter more quickly. The pressure drop near the relocated air intake, in conjunction with the blocked front grills, might cause unexpected air circulation problems, which could result in even less flow through the radiator.


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