An interesting conversation for sure.
I went from 17mpg average at 75-80mph with a stock 318 four barrel with headers and a 904 to a mildish 5.9 Magnum and the A500 with lockup (barely ever use lockup and have it turned off most of the time.)
2:73 rear gears and a 25 inch tire.
At that same 75-80mph with the Magnum and A500 I am running right at 2,100 in the rpm's and get 25mpg on the hiway.
My cam is 214/224@50 with a .512 lift and carb is an Edelbrock 1406 (600cfm)
I also run it on the lean side (around 15.5-16:1) and about 18 degrees initial with a total all included timing of 52 degrees or so.
So basically at 75-80 which takes about 1 inch of throttle at the pedal I am running a slightly lean condition and lots of timing.
Now ya got me trying to figure out why some peoples mileage stays the same or even goes down.
I'm about ready to swap in a 3:55 geared A body 8.25 sure grip, so I'm expecting I might be into the throttle a little more out of pure enjoyment, but it will be interesting to see how much mileage I loose.
Don't expect it to be much, but I do expect some loss with an 800 rpm increase at freeway speeds.
