The Stovebolt Site Forums The Shop Area Engine Shop safe speed for a 235?

im running a 235 from 1954 in a 1951 truck with the stock 4.11 rear and the original 1951 3 speed manual. what is a real max speed? ive seen people with my exact same setup take their trucks up to 65-70 and have no real issue, but i hesitate to go past 50. anyone with experience willing to help fix my irrational fear, or confirm my paranoia?
edit: engine and transmission are rebuilt and practically new.

That's a fairly low gear and 50 - 55 is really about right for your set up. You would want better brakes, modern tires, and a higher gear(or an over drive😁) to safely go higher speeds. Just my .02.

Your post poses two separate questions. First you ask what is a safe speed and second you want max speed. A bone stock 1951 1/2 ton would be safe at speeds approaching 60 provided all mechanicals are in good shape. As far as max speed, I’ll leave that up to the more adventurous among us.

I feel the same Martin's post above. My truck is a stock '52 and for me 60 mph is comfortable. Brakes and steering are mostly rebuilt except the kingpins are not yet replaced. The engine is a 216 and tires are 215/85/16.

I have the same setup as you do in a 51 GMC. Like you it feels comfortable to run at about 50 mph with it.I installed a tach just to see where the rpm's were, at 60 mph the engine was running at 3000 rpm. Just a reference point.

Look at the specifications for HP and torque on these engines. The HP figures max out at somewhere above 3500 in every example I can find, and the torque maxes out around 2K in most cases. If the vehicle is geared properly, you should be able to get up to, or slightly above the HP peak in the lower gears, and make a shift that drops the RPM to just below the torque peak. Running max HP RPM in high gear is virtually never done by anybody who drives a stovebolt these days- - - - -the sound of the wound-up engine scares them to death! If it was dangerous to the engine, why did the designers wind it up there to get the rated HP?

My Chilton service manual shows a 1956 235 (first year for the 848 head) at 140 HP at 4200 RPM, with max torque of 210 ft/lbs at 2400. Nobody I know runs their stovebolt engine anywhere near 4K RPM!
Jerry

Hi Mr. Dane,
There are folks who say you can drive the 235 at 3000 rpm all day long and that's totally true if your engine is in good nick. 3000 rpm all day may not make you feel that good, because we've become conditioned to think cruising rpm ought to be around 2000 rpm. And I should mention beyond 3000 rpm you are inviting some unavoidable inefficiencies. When I was running the 4.11 rear and 600 x 16 tires and using an accurate tach, 60 mph occurred at a wee bit less than 3000 rpm. When I switched to 15 inch wheels and 27 inch tires, the rpms increased to the same bit over 3000.

In the 60s and 70s the Dallas Public Library had an entire shelf of bound various GM publications including internal correspondence and in one I read it was suggested 55 mph in the AD truck ought to be considered top highway speed. They had been donated by the GM Arlington plant (which opened in the early 50s). This would have been the 1/2 ton truck with 4.11 rear end. As for max speed, use your own judgement. The 235 has a long, loopy crank, only 4 main bearings and spindly piston rods. And as already mentioned, you're dealing with a front end and brakes that didn't contemplate high speed driving.

In my engineering school days, I drove a 58 Chevy Del Ray, the bare-bones 2 door sedan with a 235, 3 on the tree, a 3.70:1 rear end, and 14" wheels. That car saw speeds of 65-70 MPH every day, and running mid to high 80's when we had a 75 MPH interstate sped limit in Tennessee was not uncommon. The engine will run that fast, but pickups from the 50's and 60's were built to work for a living, not keep uip with traffic on the autobahn!
Jerry

thank you all for the insight! i figured 3000-3500 rpm is fine for a short time but i was just gonna make sure before i go for an italian tune up. hopefully in the near future i will be putting 3.50 gears in the rear and then it should do some higher speeds. as for brakes mine are phenomenal and ive never had any issues, and i usually let the engine help slow me down anyway.

I remember several years ago, a company that sells ring and pinion upgrades for AD trucks stating that the swap was more favorable with trucks that had been upgraded with a 235 and the extra horsepower. Trucks that retained the 216, and especially those with the 3 speed, might have less favorable results. Trucks with the 216 and 4 speed at least had some low speed pulling power in a pinch.
Also think. Would you really want to drive 60-70 in one of these trucks in stock form? I worked as a body man in a restoration shop for years and once had the opportunity to go with the mechanic on a test ride in an AD truck that we had installed a 350 and automatic and an open late rear end in. Straight front axle and drum brakes were intact and it was a white knuckle drive . Wide tires and mag wheels caused bump steer on bumps and railroad tracks. If you want it to drive and handle like a new truck, buy a new truck. As a retired restoration guy that has witnessed some of the prices charged and some of the divorces that resulted, it is often cheaper to buy a new one.

I agree with Hotrod on this one. I don’t think you should go off “top speed” or “speed”, you should go off of Engine RPM as there are less variables (rearend gears, transmission, tire size, etc.).

Example: my 216 (3 speed & 3.55 gears) runs at roughly 3200-3300 RPMs at about 70 MPH (my Speedo is slightly off)

Chris

MPH = RPM × Tire OD × .002975 ÷ Final drive ratio
Pick a safe RPM, your tire OD, and axle ratio.
RPM 3,000
215/85/16 tire is 30.4" tall
4.11 axle
Speed = 66 mph

Easy way to calculate is to use this site to plug in the numbers here:

https://4lo.com/calc/gearratio.php

Here is my take on driving one of these trucks over 55 MPH.
You had better be adept at making all suspension and brake components like new, or know someone who can which you would bet your life on as well as others sharing the road.

Im not sure if people have trucks that are seriously falling apart or are just incorrectly assembled or aligned but mine is far from “white knuckle” when doin 70mph on the highway. No i do not run a stock engine but my entire front end and brakes are all oem stock 3/4 ton parts on my truck and i drive it at 70 with 2 fingers on the wheel just relaxing cruising along all day. Not a stress in the world when driving it. It goes dead straight and will lock up the brakes at speed if I hit them hard.

I can cruise all day at 65mph in my Suburban.

It has a 261 and a 3.55 enclosed-driveshaft rear-end.
All front-end parts are original-style and well-adjusted.
No “wandering” at any speed.

It has the Suburban’s original-equipment front sway (anti-sway) bar.

People in the rear seat can easily talk to people in the front seat.

I installed a tachometer in the '47 this past summer. It's probably one of the more useful gauges in the truck. The tach coupled with the engine noise give me peace of mind on the road in all driving situations. The '47 has a 1955 235, SM420 w/open drive shaft, 3.90 differential, and 30 inch diameter tires. It will cruise at 60 mph all day long and straight as an arrow.

What was/is the RPM at 60 mph?

If I recall correctly, about 2,500-2,600 RPM.

Using the RPM calculator at the bottom of this page:
1960 261 in 1954 3100

3.55 R&P (enclosed driveshaft)
Tire diameter (rolling diameter) = 31.5 inches
MPH = 65 (I have cruised at this speed for hours on Interstate Highways)
Final gear ratio = 1:1 (SM420 4-speed)
RPM = 2461

The highest RPM that I have reached was 3522 (for a few seconds)

To be honest, I ran my 216 at 3400 RPMs for about 3 hours one day (1.5 hour highway cruise to get lunch with buddies) no issues! That was about 2500 miles ago.

Well Chris, now we know why you're upgrading to that 261!

Andy,

I’m only upgrading so that I have a little more power for the hills. Otherwise, I’m happy with my setup. My 216 purrs like a kitten and runs better at 3200 RPM then I thought. She rides nicely at that pace. Time for a valve adjustment!

Chris

We see this question raised periodically about "how fast can my stock stovebolt go" , and I think the question of speed is best answered from a safety and original engineering/design perspective.

Will a stock stovebolt go over 50mph? Yes. Should it? Given the straight axle front end, 4:11 rear end, primitive steering, drum brakes, and other design & aerodynamic aspects, my thought is no. I have no doubt that our trucks could run at 70 mph 3,500+ rpms, but they were not designed for that.

Compare to my 1998 F-150. It runs 75mph at about 2,800 rpms very comfortably. Why? Because the design parameters allow for that. The brakes, steering, and suspension were designed for it. If 50 years from now, someone asks "Will my F-150 run 110mph?", what would your answer be? It would probably be "It's not designed to do that and while it technically would do it, it poses a safety hazard doing so."

If your intent is to -safely- run 70+ mph, then I think it is your responsibility (for the sake of others on the road) to spend a significant amount of money on necessary steering, suspension, and braking upgrades that will safely support your need for speed.

I run my 53 with a 261 at no more than 40-50, and know that I can stop or make a sudden steering change if need be, and enjoy the cruise

im definitely not gonna push it to 70 on the freeway, im just tired of filling up the tank every few days. also where i live in florida the chances of me hitting something that would cause bump steer is darn near 0, on top of that im running stock wheels which are practically rubber bands. as for brakes i dont think ill ever have an issue. i drove a deuce and a half owned by our county, got it up to 60 and with practically the same setup in my truck had no issue slowing down. my guess is some older folks cant push the pedal like they used to. my knees are still good, for now anyway!

All big trucks are still using straight axles up front and cruise all day at 70-80 so thats no big deal. I TRY to stay at 65 in mine but all of a sudden you look down and its like silk at 70+ and climbing and i just slow it down to stay safe in my own mind because im not in a hurry in that truck but i can drive it with my knee at 70mph all day. Good tires, correct toe and the right gears and it will just float along.

Straight axle: no camber change or bump steer during suspension travel
"Primitive steering"?

The original question is missing one key piece of information - tire size. The diameter of the tire is going to make a huge difference in potential cruising speed. Once we know the tire size we can give an accurate safe cruising speed for that drive train based on facts.

We cannot, however, speak for the condition of the truck. As long as everything from the front leaf spring shackles to the rear leaf spring shackles is in great shape and properly maintained there is no reason one of these trucks could not be safely run at 70 mph. The drum brakes work amazingly well when properly maintained and if straight axles were so dangerous they wouldn't still be putting them under school busses.

My '53 GMC has served as my daily driver for the last 10 years. I am well aware of its limitations and its capabilities. I am always surprised when someone suggests that these trucks should never be driven faster than 50 mph. Even with the wore out old '49 216 ill fitted under the hood, I don't hesitate to run 65 - 75 mph for hours. Of course, I am geared better than stock and run an anti - sway bar.

My 1958 Del Ray coupe with a 235, 3 speed, and 14" tires used to run high 60's to mid 70's regularly, and it had a 3.70 rear axle ratio. When I got in a hurry, 80+ for several miles was not uncommon.
Jerry

I have a completely restored 54-3100. With the original 650x 16 tires and it will run 70+ on I-75 for hours. If I need better traction for safety I change the wheels and tires off of a late model 4x4 Suburban. A 235 is a modern engine. Doc.

I would have to drive one of our trucks in near stock form at 70+ to be able to truly answer the question, but I can't imagine having to make a sudden steering change or slam on the drum brakes at that speed. I have heard stories about these trucks, being light in the back end, turning circles and even flipping on their sides during panic stop attempts.

Just remember, better brakes for faster speeds.

If I keep "proper distance" between me and the car in front of me, and, if I am sober and driving "alertly", I can easily make a safe emergency stop at/from 65 mph.

"proper distance" is one car/truck length for every 10 mph.

I do not go over 65 on any road that has cars going/coming in both direction (with no median strip).

I will not tell you my one-time highest-speed on a 5 mile straight run on a country road (no other traffic in either direction).

Come on Tim, we’re all friends and we won’t tell!

I like to count following distance in seconds rather than car lengths. For me a safe distance is 2 seconds from the car ahead of me. If I am hauling a load I might try to keep 3 seconds apart.

You have to go with your gut. I have a 100% stock 54 3100. 235 with 3 speed. I am comfortable running 50-55 for extended periods and have gone to 65 but anything over 55 make me uncomfortable. It just "feels" like I am running the engine too hard to maintain for any length of time. The other factor some have eluded to is handling. These trucks were not designed for that type of speed. The brakes, steering and suspension don't perform like a modern vehicle. You really have to be on your toes at higher speeds.

93 mph for a few seconds (I checked, my pants were clean afterwards).

Never again - one time by myself and one time with my mechanic/painter friend (a witness/rider) - who was in awe.

Your engine must have been begging for mercy! LOL

To gauge how much noise the engine is actually making, take the fan off and then make a highway speed run. If we could figure out how to put a thermostatic fan clutch on that only drives the fan when the air coming through the radiator is hot enough to need the fan (idle/traffic) I believe higher speeds on these old rigs would be much more comfortable.
Jerry

Ive been meaning to ask that same question but never got around to it. Is there a known thermostatic fan that would fit a 63 gmc 305e?