The Insight pre heats the intake air via the coolant lines that goes through the "throttle plate" body. This is done to decrease emissions and for economy. The black box you refer to is a "baffle box", (resonator) for the intake air to lessen the sound of the intake air being "sucked" into the engine. If you measured the area of the standard intake pipe opening versus the opening of the "hanging hose" you would see that the "hanging hose" is much larger. This allowes the engine to "pull" a higher volumn of air giving more power. You are also possibly getting warmer intake air as the area where you are receiving fresh air for the intake is one of the hotest spots in the engine bay. That's why I have my air cleaner for the turbo mounted where it is as that was the "coolest" area in the engine bay. You should be able to cruise at high speed with a lower percentage of throttle opening, and your acceleration should be "brisker". Better mileage could be contributed to the fact that you get to cruising speed quicker. (Fast acceleration vs slow acceleration)(That has been debated many times).........My opinion.