i just bought a 91 firebird with a 305 tpi and a 5spd it has headers and a 3.73 posi rear end. im just curious if anyone out there has the same set up and what kinda gas mileage i can expect its not a huge concern but im wondering. i plan on putting a k and n air filter on it and an ecu chip.

Are you sure about the 3.73 gears? I know they came stock with 3.42. In stock form with the 3.42 I was getting about 14-15mpg in the city and about 24 mpg on the highway. RPMs at 70 mph were around 2200-2300. If you have 3.73s that will hurt your fuel economy a good bit.

my best combined was 23.85 mpg, but mostly highway with a little city.
91 ta 305 tpi 5spd all stock