Consumption

Hello, had asked me some time ago about a Pontiac Firebird or Trans Am. Was with my father with some Firebird owners and must say that the car is still great. All that displeases me and also my father is the high fuel consumption!!! Is there no chance to reduce it somehow. My father meant you can install another engine, does it all ? and is it advisable to do so ? Thanks schopnmal for your help.