Just wondering if my fuel mileage sounds about right. I dropped in a 355 with about 400-425 horse, timed at 12 degrees, idles at 650 rpm, a borg warner t10, 10 bolt auburn posi, 3.73 richmonds, moser 28 spline axles. When i'm doing 60 mph i'm running at 2500 rpm. I don't get on it that much, but i've been averaging 10 MPG. Is this normal? Should it require a break in period, as I haven't driven it for more than 300 miles yet? By the way my car has been running hot around 210-220 degrees.

 

That's about what I get

 

Thats about a normal temp.Your mileage may get better with break in my wife had a 05 tahoe that improved after a few thousand miles when she got rid of it and got an 06 maxima it did the same thing just noy as big as an improvement About a 3 to 5 mile MPG change.MY car should be runnong this week so i'm interested to find out the differense in mileage from its old 305 to its new 350 after break in.Are you running carb or still on factory TPI/TBI?my mildly modified 305 TPI got about 24 to 25 mpg on the interstate with the stock 2.73's