I have a 83 305 Grand Prix that I'm considering putting back into daily driver status. It currently is getting about 19mpg in a 60% Hiway, 40 City mix. The specs are 305, CCC Qjet, turbo 350c, and 2.29 rear - all stock 145k miles. That 2.29 rear makes it a dog off the line, so I'm thinking about going to a 2.73 or 3.08 rear. I'm thinking that my mileage shouldn't change much since the slight decrease in hiway mileage would be offset by a slight increase in city mileage. This make sense? Would I do better by transplanting the 350/300 700r4 combo from my Chevelle with a 3.42 rear when I install the BB? Thanks.

Tino,

I like the idea of putting the 350 w/700R and 3:42. My 85 T/A has a 305 w/700r and 3:23 and is fun to drive and knocks out 20 mpg

Bill