[t vago]

Originally Posted by mechman600

Basically, you are virtually attempting to reduce the volumetric efficiency of your engine by making the air less dense - not by reducing the volume of air, but the mass of air, and hopefully reducing pumping losses in the process.

Not quite. The reduction in volumetric efficiency is an unavoidable side-effect of what the HAI is doing. Consider a vehicle that we want to move at a constant and steady speed.

Here, let's look at this graph from this here website:



This graph is a representation of what goes on inside a cylinder of an ideal gasoline engine that has a throttle. It is a plot of in-cylinder pressure against the swept volume of the cylinder as the piston travels back and forth. The intake, compression, power, and exhaust strokes are all represented here.

Note the two loops. The first loop, that has no color, is the power loop where the air/fuel mixture is combusted to produce mechanical power. The area of the first loop represents the total mechanical power that is created when the fuel/air mix is combusted.

The second loop, in grey, is the pumping loop. The grey area represents the work that the engine has to perform just to expel exhaust gas and then suck in more fuel/air mixture. Two values are crucial to determining this area: P(atm), which represents atmospheric pressure; and P(man), which represents the intake manifold vacuum. If you subtract the grey area from the power loop area, you get the total remaining power available to do things like overcome mechanical friction, turn the alternator and water pump and any other engine accessories, and ultimately drive the vehicle forward.

Now, remember that this graph is a representation of pressure against swept volume. The mass of the air/fuel mixture does not directly relate to this. It is the pressure that is important. For a given part-throttle load, the mass of the air/fuel mixture must remain constant in order to support that load. This, however, does not need to hold true for pressure.

Now, the HAI is relevant to this graph because it reduces the grey area. Specifically, the HAI pushes the P(man) value upward to become closer to P(atm). This has the effect of reducing the grey pumping work area, which frees up mechanical energy to do things like push the vehicle forward.

Now, if we left the air/fuel mass alone in this scenario, the result of having more mechanical work to push the vehicle forward would be to cause the vehicle to move faster. As we would want our vehicle to continue moving at a constant and steady speed, we would instead adjust the throttle in order to maintain the vehicle at its steady speed.

Originally Posted by mechman600

Have you thought of the effects of increasing the humidity of your intake air? I know, I know, water injection has been discussed to death on this forum and it has no effect. But what if you combine it with a HAI?

Assuming a fine mist spray that allows the water to turn into water vapor, and assuming that the water was at the same temperature as the air to begin with, then the added water vapor would provide a throttling effect without the inefficiency provided by the throttle body. This would cause the intake manifold vacuum to lower, as well, further reducing the gray area in the above graph.

However, there are several practical real-world problems associated with water injection. HAI water injection is a subject which deserves its own thread, separate from this one.

Originally Posted by mechman600

However....I see a problem for us folks with automatic transmissions. Having a larger throttle angle is going to make the transmission quicker to kick down to a lower gear.

Yah, I'm already seeing this. It would seem that it takes less gas pedal than before, to send my truck into open loop acceleration. Kickdowns also appear to happen with less gas than before. I suspect this is the engine computer's way of dealing with the elevated intake air temperature.

Originally Posted by mechman600

Maybe steady cruising in high gear will be impossible because the tranny will keep kicking down. Our electronicky cars don't have kickdown linkages to adjust either. Maybe this doesn't matter, who knows.

Only way to really find out is to experiment!