The Stovebolt Site Forums The Shop Area Engine Shop Best RPM To Run A 235 Babbet Pounder At????????

I have a 1942 Chevy 1-1/2 ton truck that I ran the numbers on (tire size, gear ratio, and speed) and at 50mph I would be running at 2600 rpms. Am I asking for trouble at that speed or not. What is the best rpm to run this engine????? Thanks for your help!!!!

Marv.

I've read that the work trucks ran all day with the governor set at 3000. I personally wouldn't be concerned with 2600.

I have a 1942 Chevy 1-1/2 ton truck that I ran the numbers on (tire size, gear ratio, and speed) and at 50mph I would be running at 2600 rpms. Am I asking for trouble at that speed or not. What is the best rpm to run this engine????? Thanks for your help!!!!

Marv.

2600 rpm sounds OK to me?

I thought a '42 would have a 216. RPM's still dont seem excessive.

A 235 was an option in 1942, on 1.5 ton trucks.

Chevy began production of a 235 in 1941 as an option in the 1 ton+ Big(ger) Bolts. Relativly rare. A scoop oiled babbit engine like the 216, same bore and stroke as the later pressurized 235.

here is my speed chart for my 40. it has 7.50x16's on it with a 4.56 rear. this chart was generated from a web calculator that i have verified with my westburg tach and my gps.
MPH RPM
40 2009
45 2261
50 2512
55 2763
60 3014
somewhere i read where gmc designed for a continuous engine speed to be 2/3rds of max.(cant speak for chevy) so with that being said 2/3rds of 3400 equates out to 2278 which is 45 mph on my truck with the pointer sticking straight up and down on the speedometer. not to say you cant run it higher but i found that all my trucks run their best, sound their best and i can hear the best when i run that 2/3rd rpms. the sweet spot on my 40 is 2450 which is 47.5 but i run 50 on the big roads when i want to get somewhere fast. what is the condition of your engine? mine is freshly rebuilt.

2/3 of governed rpm was considered the rpm for fuel economy. However if the engine is in good shape, running at the governor doesn't hurt them. We never had a Chev, but when we used GMC to actually haul loads of gas, we even bumped the governor up a little or removed it. As long as we had enough radiator to keep them cool, they were fine. We used to get radios out of Ford cars which were also 6v neg ground with heavy 6x9 speakers and that did wonders for drowning out the engine and wind noise.

Positive ground Kenneth?

Not for another decade or so.

My numbers for the rpms 2600 is what the Randys Ring and Pinion calculator said. Tires 34.5, 5.43 ring and pinion at 50mph, 4 speed trans. Engine has 55,000 miles on it.

Marv.

Iron pistons were what kept engine speed down back in the day.

Panic,

I know you're correct, but I don't know WHY? What happens with the iron pistons that doesn't with aluminum (or whatever)? The iron get too hot, expand, and seize in the cylinder?

-Michael

I think they just weigh a lot more...

The cast iron pistons do weigh more than aluminum, they also take more time to warm up and fit the cylinder than aluminum. The amount of force put on the connecting rod is greater with the cast than the aluminum. If the engine gets hot enough to stick the piston to the cylinder wall your going to have bigger problems than a piston dragging against the cylinder wall. If it starts to stick to the cylinder wall you can figure on a bore job with new pistons at the least. I you ease your truck up to speed you should have no problem. I drive my '50 216 50 - 55 and just take it easy, once up to speed things go along just fine. With a bigger truck you may be a bit slower. Just take your time getting it up to speed.

The heaver piston has more inertia which puts more stress on engine components as the RPM goes up. (i.e) Newton's Law: When at rest, tends to stay at rest, when in motion tends to stay in motion. Pistons have to stop and start at the end of each stroke.
Easier with light pistons than heavy ones. One man's opinion.

I could never imagine running my 235 at anything near 3,000 rpms. With my Patrick's 3:55 gears and big tires I cruise 60mph at around 2,200 rpms. Purrs like a kitten.