OK.. if you put the smaller pully on the SC with a new exhaust and a high flow cat, theroreticaly this will increase your fuel economy. Is this true?

 

not likely, more performance, more efficiency (maybe, but doubtful), more boost definatley.

 

But are you not getting the additional boost from more air being compressed into the cylinder and causing a stronger combustion of the fuel?

 

Pretty much depends how heavy your foot is. Usually with more performance peoples feet get heavier :-)

 

Won't the MAF detect the increase in intake air and dump more fuel in as well then?

 

It depends I think on how its set up. If your running more boost, usually you are consuming more fuel, otherwise no more boost would get in. On the other hand if your MAF records the difference and compensates, or you change your MAF setup, you could either run better fuel economy or at least the same.