Rebuilt and less than 1000 miles on the OA-331. 11.00-20 NDT tires and a hard top. I got 5.3 according to my speedometer on my last trip to Houston (130 miles). My speedometer is about 12% slow because of the bigger tires however. That gets me to right at 6 mpg. I was able to run 60+, but engine heat kept me at 45-50 for most of the trip. (This was in August and it was over 100 degrees outside.)
I topped off the tank, spent hours winching a motor home around and then dragged the motor home to my place 130 miles away. With my foot nailed to the floor in 3rd and 4th gear and a few down hill runs in 5th all between 24-45 mph. I topped off once home and my milage was 5.1. I am still burning that tank down since I normally only drive it 20-30 miles a week.
Those are my only actual trip numbers. If fuel stays like it is, it will get driven a lot more. I think the 6-8 mpg can be reached with 9.00 tires (hills kill this thing) and 45 mph. It will be a stretch though.
Before my Houston trip, I did a shake down run to another members house 35 miles away. I used a broom handle to measure the fuel before I left. I ran it at 65 mph according to my gps the entire way. I measured the fuel again and I used 2-1/2". Every 3" is 10 gallons. I drove home at 45 indicated top speed letting the hills slow me down instead of attacking them. I used 1-1/2" of fuel which gives me 7 mpg exactly.
Those are the most accurate numbers I can give you right now. I will add that I have no idea what timing I am running on the engine. The idiot that rebuilt it 25 years ago put the balancer on indexed wrong. I of course didn't figure this out until I had the entire truck back together and all buttoned up. So, since it runs great and doesn't ping, I haven't gotten motivated enough to pull it apart and fix it. The timing might be spot on as far as I know too.
