Gearing is everything as far as fuel economy is concerned. I am running a 350 V/8 with a 700R4 OD trans.and 3:90 rearend.getting 20 MPG.If I was running a regular 350 or 400 Hydramatic or a regular 3 or 4 speed manual,I would have to have a 3:08 rearend to get that kind of gas mileage.The OD trans is about .78 to 1 ratio going to the rear,whereas a 350 0r 400 is 1 to 1 ratio.Hope this helps.
