Comparing Warm Air Intakes (WAI) & Cold Air Intakes (CAI)
My basic point is:
With respect to air intake temperature, maybe there is no difference between a Cold Air Intake and a Warm Air Intake regarding Fuel Economy (FE). Please read on.
CAI:
From what I have gathered, in the performance tuner world, a cold air intake is one of the most basic mods one can do. Power gains can be small, especially for smaller engines. 0.5% improvement is a good minimum starting point for the power gain.
The idea is that air intake is supposed to be placed farther away from the engine than stock, thereby sucking in colder air. The lower the temperature of the air, the denser the air. More air than stock needs more fuel to keep the fuel ratio satisfied. At any given throttle position, this should result in more power than stock since more explosion mixture is being introduced to the explosion chamber.
For the sake of this discussion, let us assume that the only advantage here is the denser (colder) air. (Other advantages of new intake plumbing: less restriction. This may be a result of a more-porous filter, larger intake tube diameter, smoother plumbing, or less bends and turns in the plumbing.)
A cold air intake does not result in a richer mixture of fuel. If a mass ratio of 14.7 to 1, air to fuel, needs to be maintained, then the engine will keep it there. A rich mixture is a mixture with less air (flip side of the coin, more fuel) than the stoich mix requires, and therefore would not be the result of a CAI. (This could be the result of a reprogrammed ECU)
WAI:
A Warm Air Intake is placed closer to the engine than stock to pull in warmer air. The greater the temperature of the air, the less dense the air. Less air than stock needs less fuel to keep the fuel ratio satisfied. At any given throttle position, this should result in less power than stock since less explosion mixture is being introduced to the explosion chamber.
A warm air intake does not result in a leaner mixture of fuel. If a mass ratio of 14.7 to 1, air to fuel, needs to be maintained, then the engine will keep it there. A lean mixture is a mixture with more air (flip side of the coin, less fuel) than the stoich mix requires, and therefore would not be the result of a WAI. (This could be the result of a reprogrammed ECU)
Stoich:
The modern engine is trying to keep a 14.7 to 1 mass ratio of air to fuel.
http://en.wikipedia.org/wiki/Air-fuel_ratio
Hypothetical and demonstrational situation:
So normally, if one is cruising along at 55mph, say the car needs 25 units of power to do this. And to achieve this power the engine needs to run at 2200 rpm.
Now say one has a WAI. Cruising at 2200 rpm, the engine is pulling in less air, and so it is making 24 units of power, and runs at 53 mph. In order to cruise at 55mph, the engine needs to run faster, at 2250 rpms to achieve 25 units of power.
Next, the same vehicle as a CAI. Cruising at 2200 rpm, the engine is pulling in more air, and so it is making 26 units of power, and runs at 57 mph. In order to cruise at 55mph, the engine needs to run slower, at 2150 rpms to achieve 25 units of power.
(assumption about to start)
But all situations should be consuming the same amount of fuel.
(end assumption)
Problem:
I suppose the engine is consuming the same amount of fuel to make the needed power at any rpm?
It seems as if the needed rpm is shifted, but not the fuel consumption?
Point of difference:
The point of difference between CAI, stock, and WAI would be at WOT. At WOT (Wide Open Throttle) the engine should be making the most power (& burning the most fuel) with the CAI, and be making the least amount of power (& burning the least fuel) with the WAI. Maybe this is the only time there is a difference. I would not call it an efficiency, I think it is more of a difference.
Personally, I'll stick with the CAI because when I need the vehicle to go,
I need the car to go! And now I realize that with a CAI I am not loosing any MPG when I am trying to be economy minded.
A new direction?:
Maybe eco-modders should be more concerned with gaining the other benefits of a new Air Intake, namely less restriction. This may be a achieved by a more-porous filter, larger intake tube diameter, smoother plumbing, or less bends and turns in the plumbing.
Less restriction should result in better overall breathing efficiencies.
Reprogrammed ECUs for leaner fuel ratios. I do not want to touch this subject any farther than that!
Please Note:
1 I bet I am wrong somewhere. Please, someone put it right!
2 I am just a college student, studying marketing. I have no formal background in any of this. But I do have a hunger for understanding how things work.
3 All of my references are to fuel injected engines with an ECU. I have no knowledge of carburetors.