There is a recent post on one of the Thunderbird forums, regarding the gas mileage of 55-57 Thunderbirds with 292-312 Y-block engines. Some owners reported 7-10 mpg, others getting 9-12, another getting between 13-14, and another claimed 20 mpg on the highway, in overdrive. Having inherited my 55 T-bird, I drove it just a couple of times before beginning restoration, so I have no idea what kind of gas mileage I should expect. 7-13 mpg is nothing to brag about. Are these numbers typical? They are awfully low for a small v8 in a 3,000-lb. car. Is there an explanation, other than the given examples are parade cars that are seldom driven on the highway? 

I'll have an O2 bung installed in the Sanderson reducer during rebuild. RPM @ 65 should be about 2200. Cam range is 1800-5000. C4 transmission.