Hi Patrick. You can get a slew of opinions on this subject. Here's mine: They cruise well and economically at 2000~2300 rpm...smoothly and effortlessly as long as you're on relatively flat roads and not in a headwind. At 2500 to 3000 rpm, you can drive your engine all day long but gas mileage will decline steadily the closer to 3000 you get. Trust your ears and your sense of feel. There is a big difference in driving one of these engines at 3000 to 3500 rpm versus driving a Honda, Subaru, Toyota engine at 3500 rpm. The harmonics are altogether different.

I had an uncle who was a cotton farmer. His analysis of the 235 (very similar to yours) was "run these at the right rpm and you can depend on them almost forever. Run these too hard and fast and you can depend on them for a little while. It is your choice." He used them to run irrigation pumps and some of his were still going after almost 20 years the last time I saw them.

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end