Intresting this comes up now. Today on mythbusters, they were testing claims of gas additives and gadgets that supposed to improve gas milage. They were using a chassis dyno, the car selected was a late 70's G body Olds. with a V-8 and 2 barrel carb. It got 16.7 MPG @ 35 MPH, and 25 MPG @ 55 MPH, by the way not one additive or gadget increased the milage. I'm assuming that it probably had the same gear as my 1979 Elky came with which was a 2.48 and a 350 trans.
Zip.