would the D15Z1 be able to be swapped into any EG hatch and still maintain it's fuel saving capabilities?

or are there other things that work in conjunction with the motor i'd have to buy and install also?

 

In my honest opinion, unless you have no other choice I would not get the D15, I would look for a D16, you will have the same gas milage savings with either engine, and you will have more hp in the process. Now if you have no other choice in the matter, but to take that D15, then all you will need is all the parts of the engine (intake, header,TB and tranny) and the ECU for that engine out of its donor vehicle and you will have the same gas milage it had from its last car.