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? 

The issues with the "Loadomatic", pre 1957 distributors, which don't have centrifical advance  has plagued Y-block engine owners for years.. Because, if using a 1957 & later Carb with that vacuum only distributor, the setup will not work properly. Nor will an original stock Holley 4000 'teapot" work properly as is, with the 1957 &  later Distributors. For proper info on that later issue," Link" from this site to "Ted Eaton's Balancing" site & scroll down to his instructive article on modifying the Holley Teapot carb to work with the 1957 & up distributor..    


Paul

The "Teapot" carburetor doesn't care what distributor is used, although it is true there is no source of ported vacuum below the throttle plates. That's what the carburetor modification is about.

But manifold vacuum (from whatever source derived) can be made to work perfectly well with a dual distributor, I wouldn't let the carburetor be a show stopper when considering whether to ditch the LoadOmatic. Achieving a perfectly steady idle RPM can sometimes be an issue (which incidentally was why the "ported" type of vacuum signal was invented).