As with anything else there is a happy medium to gearing.First of all I was lucky to find my 700R4,a freind of mine built it for racing,and he decided later that he would rather have a 4 speed manual tranny. I just happend to have a 4 speed M22 in my pickup at the time,so we just traded trannies.So here we go,as far as running tall gears to improve mileage there is a limit.Which even with a turbo 350 or 400 seems to be about 3:08. To my way of thinkling,anything taller than that for instance a 2:73 is a bit much. You reach a point where even cruising at road speed you are laboring your engine quite a bit just to maintain a decent speed.Hence the 15 MPG with 2:73 gears.If ya wanna do some math heres how an OD trans helps you out,even with 4:11 gears. A 350 or 400 Turbo,or a standard 3 or 4 speed has a ratio of 1 to 1 going to the final drive,(rearend) whereas a 700R4 runs around .78 to 1 ratio to the rear.Same way with any OD trans. The numbers might fluctuate a little but they are all in the same ballpark.Like I posted before my 55 has a healthy 350 smallblock hooked to a 700R4 then into the stock 3:90 rear. Plenty of performance and 20 MPG all day long.Most of the guys I know who are running a 350 or 400 Turbo auto are running 3:08 gears,which seems to be about the limit.I am pretty sure my 700R4 came out of a 1984 Chevy.One other thing on the 700R4,the first gear is very low,I can bark my rear tires any old time with that setup,and if I hold er down she will bark again going into 2nd and 3rd gear.
