A stock 235? After owning and driving these engines for about 60 years, I would say something around 25~2600 rpm for a long road trip would be the most I would ever consider suggesting to you. If the engine has been rebuilt professionally to OEM standards, 3000 rpm would be okay, but you also have to weigh reasonability vs economy. The 235 at 3000 rpm certainly will not be in the "economy zone." And it will sound like you're abusing it at that speed. If the 235 has several thousand miles on it, bad things can happen if you push it too hard. It has been about 6 or 7 years but a member on one forum I belong to posted a picture of a piston rod sticking out the side of his 235 with the message being something like "it sounded like I was overworking it before it exploded." The 235 in stock condition is anything but a racing engine. It is nothing like the small block V8 in any way. Have you ever been in a truck that threw a rod? Here is the sequence of events: horrible noise followed by a seized engine with possible loss of control (depending on where you are and road conditions...curve, wet road, etc). Driver startled out of his/her wits. If it happens on the upstroke, the piston keeps going on up to the head. If the rod is thrown while the piston is coming down, it can go through the side of the block. In any event the engine is instantly seriously imbalanced and not something you can drive home. Often the engine can't be repaired.
