The Stovebolt Site Forums The Shop Area General Truck Talk Comfortable cruising RPM for 261 eng.

Mike, I don't know about the 261 but in 1959 GM changed the 235 in a move to help reduce bumper to bumper or slow moving traffic smog. They changed the camshaft and the change produced more torque at lower rpms...nearly a 20% improvement. There used to be a GM letter sent to all dealerships explaining this on the GM Heritage pages but I haven't been able to find it since they "cleaned up" the site years ago. I have a T5 (fifth gear of .86) and at 60 I'm about 2000 rpm...which is the max torque rpm of the 1959 235. I feel safest at 60~62mph. What it means for me is the first 3 gears match the OEM final drive ratios of the 1952 AD truck as GM designed it, fourth gear goes to 1:1 and that gear drops rpms by 25% and then fifth drops another 14%. Is it perfect? No, in oncoming wind or notably hilly areas I will need to drop back to 4th gear and I lose that 14% fifth gear bonus but it was the best compromise I could make. I can still load 1000 pounds of "stuff" in the bed and drive without damaging the clutch or overstraining anything and the reduction in rpms at 60 mph is dramatic and the engine doesn't mind it. If you look at the torque curve for the 1959-1962 235 you'll see at 1600 rpm you're pretty much at max torque and you remain there on a flat line until around 2800 rpm before you start falling off. My suggestion is to stand on the shoulders of the GM engineers. If you had bought an El Camino with a 235 you could have also had a 3 speed with overdrive (a 30% reduction in 3rd and OD). It is about 300 pounds heavier in curb weight than the AD pickup. You would have had a 3.70 rear end and 3.70 x .7 is around 2.60. Depending on the year of production you might have had a 4.11 rear end and that final drive ratio would have been around 2.87. A friend of mine owned a 1960 and had OD with a 3.70 rear end and the high payload option (I think it allowed him to haul up to 1100 pounds). Somewhere between those two final drive ratio numbers will be okay as the GM engineers saw it. Mine is around 2.65 or so. Good luck!