The Stovebolt Site Forums The Shop Area Engine Shop 3:90 -235-safe rpm

Hi....a 1957/235 stock 3100pu..with 3 sp.+ 3:90....what would be considered a safe RPM number? Is 2500 at 55 (3rd gear) to excessive for the 235?
T/C Steve

From what I've observed with my 1960 235 over the past 6000 miles, the optimum operating rpm, where I get my highest vacuum reading is at about 2300 rpms. Cruising at 55 mph with a 235 at 2500 rpms should present no problem for a sound engine and should yield a relatively high vacuum reading. In fact, I would go so far as to say that 65-70 mph if under 3000 rpms would not overtax your engine but wouldn't be as economical.

Dave

THANKS Dave,
Its cool that you have actual mileage figures at RPM that takes the guess work out for the rest of us! T/C Steve

My old man's got a stock '59 1/2 ton with 235 and 3.90 gears.
It is driven often at 55 to 60 mph and feels pretty comfortable at that speed as well.

With a straight front axle I think 55 is fast enough and of course with drum brakes all around it can be fun. I was just wondering what these old engines were worked at RPM wise as they were farm tools. My Grandpa had a 48/3100 with 216 but he never went over 45 as a rule...not that I can remember. Now that I have an RPM gage I need to learn a set of new rules. T/C Steve, Steve

Stock 216-235's in good condition are safe to operate up to 4000 RPM. After that do it in small bursts. As a kid all of us used to run the pants off of these things and I never saw one come unglued. You guys are afraid of them, I say run it like you stole it. You'd be surprised just how good they are.

I personally know of balance 6's that run over 7k.

MAN....4K RPM.... I'd be swaying and praying! At over 50 years of age I think I'll keep her in the 2k range. BUT..its good to know that these old ladies will stay together.....makes me feel better! Thanks, Steve

These old 6's are done by 3000 rpm in stock form. With liberal amounts of money applied, they can be made to spin at higher rpms, and generally they will hold together until 5-6K without concern in stock form. My suggestion would be to gear it correctly for intended use. With a stock engine, if you figure 3000 rpm at 70 mph, and adapt your rear gears and tires to match.

Devin

Who, me,

I couldn't agree with 53moneypit more! I bought my '56 in 1972 with who knows how many miles on it. I drove it until 1975 without a care about rpm. The engine finally got to tired and I replaced it with a used rebuilt 235 from a 1957 pick up that ran well. I went right back to driving the h**l out of it. The drive line was a stock 235, stock 3 speed, and stock 3:90 rear end. 31" tall tires. From 1972 to 1984 I probably put close to 300,000 miles on the truck, a lot of it at highway speeds. If the power train is in good shape, don't be afraid to drive it and let it know who's boss!

best wishes,

Les

I have a 216 in my 1940 with a 3:90 rear and a T5 transmission and every time I take it out ,I can't believe how well it runs and the torque that little engine has. In 4th gear, which is 1:1 ratio as you would have,50 mph is no problem, but the 5th gear overdrive is nice because everything just kind of relaxes.

Roadmarks,

You are right on. I have been saying the same for years. If it is in good shape, drive it like a truck and not museum piece. I have put many thousands of miles on this same setup. I never worried about RPM limits. The engine would take care of that for me.

I one drove 475 miles on the freeway in 6 hr and 45 mins in a stock 56 with a 235.

Hey with all you guys having 3:90 gears and 235's can you tell me if a 3:90 rack and pinion from a 54 will fit in a 49 carrier/torque tube assembly.

well I meant ring and pinion and I found out it would work with the earlier carrier housing.

I run a 0.60 over 261 cu.in. 6cyl., with a howards m4f cam and fenton headers,duals all the way to the rear bumper. A holley/weber carb from Langdons, 390 rear gear 255/70-15 rear tires.Turns about 2600-2800 rpm at 60 mph. all day long. gets 18 mpg on the highway @60. Been driving it like that for 5yrs.

Craig,

Wait to hear from someone else, but I think that you will need to use the 1954 ring gear carrier/case with the 1954 ring gear (and 54 pinion) in an earlier rear-end housing. You might already know about that, but I thought this should be brought up.

I agree with 53moneypit. These things were built to run 3,000+ all day long. If you want to put them under load at 2k like modern engines, you will be lugging them. This is especially important with splash oil rods. They depend entirely in hydrodynamic lubrication because there is no oil pressure at the rod bearings and hydrodynamic lubrication requires speed. Just because the old engines make a lot of noise with steel fans and solid lifters doesn't mean that they are going to come apart. Horror stories of splash engines throwing a rod usually starts with an engine that has been lugged and develops bearing clearance. And then with this excessive bearing clearance, it throws a rod when it is revved up.

I pull over a mountain pass starting at 700 hundred feet to an elevation of 1900 feet using 3rd gear at 65 mph @ around 3k rpms. I really think the 'Poor Man's Overdrive' aka, 215 85R 16's is the way to go for the straight 3 or 4 speeds w/o overdrive.

Regards,

Cosmo