I to have 7.50-20's that I am thinking of switching out to 8.25's when the time is right. That will work out better for mpg if running on flat ground. My area is hilly, so it may actually hurt my mpg - more likely vacuum will drop and enrichen mixture while retarding timing.
Some folks think i run her too hard, but this is how I look at it. I have many decades of experience running stovebolts in a marine application. Redline was 4200RPM under load, and cruise was 2/3 of redline. That makes the cruise RPM 2800 (for thousands of hours). With 37" tires and a 6.17 rear that cruise RPM equates to 50mph. This is the max I will push her and I will stay under that as much as possible. And of course, popping up to 3100rpm/55mph is doable for short time for unique highway situations.
Do you have a 216 or a 235?
