I have a max RPM of 2350 on my 8v-71 Detroit running through a RTO-9513 Road ranger (single Overdrive trans) and then through a Rockwell T-1138 Overdrive Transfer case to 7.20:1 axles, I also bolted on 6 new 11R22.5 wheels and tires to help as well,... Before I pulled the 350/5 speed out I could get 60 mph wound out at 4500 RPM with 8.25-20's
the spreadsheet says that the big Detroit @2350 will get me 52 mph in 5th direct (12th gear) and 72 mph in 5th over (13th) and 1800 should be 55Mph and 2100 should be 65... very comfortable RPM for the old girl,,, who is used to pulling 75,000lbs of TD-25 on a 20,000 lb detachable in that old looserville 9000 ford and will retire pulling 12,000 or so of GMC pickup around...
We get 15MPG bob-tailing around in the 69 Brockway 361 twin screw with a turned up 6-71 and a bit better in the 70 Brock 361 Single rear so I expect to see somewhere in the 12-15MPG range at highway speeds.. A bit more motor and in between on the weight and they are 10 speeds with no overdrive (4.33 gears),...
Jimmy in a Jimmy...
