The Stovebolt Site Forums The Shop Area Engine Shop RPM Sweet Spot for 216 and late 235?

What is the 'runs great all day' RPM level for the original 216 and a early 60's 235? I'm looking for the comfortable cruising level and the maximum I can run--without excessive strain--on my '48 1 ton dually with a 8800 lb. GVW. I want to change out the final drive from the stock 5.14 to either the 4.57 from a 3/4 ton or a 4.10 from a later year. I'm trying to balance speed and load capacity using the original 4 speed transmission. Experience and advice appreciated!

I installed the 4.10 on my 1 Ton single. At 60 mph I am turning around 2800 with the tall 16" radials. 50 mph is the sweet spot for me. I don't haul anything.

I don't think that comparing a 216 motor to a last generation 235 is a fair comparison. Its a bit of apples vs. oranges. As to how hard you can run an engine has many variables that relate to each engine. If you look at the driving conditions when the 216 motors were sold and then look at the driving conditions of the early 60's you will find 2 different situations. Engine condition also plays a big part of how hard it can be run and how it will perform. Your '48 3800 should be able to run 40-50mph with a 216 that is in good tuned condition. A later 235 may run some faster. You should also consider the brakes and steering before you get out on the road and wind your truck up to cruising speed because sooner or later you need to stop and you also have to keep it between the lines on the road.

Brakes and steering always come first. Most of my driving is rural, under 30 mph but sometimes I go to town on a two lane,55mph road. Sure I can run at 40 but I'm not crazy at holding everybody up if I don't have to. By juggling rear end ratios and engine choices I'm just trying to find the most flexible setup. What I don't know is where each engine runs its best. 2000 rpm? 2200? 2800? The factory specs on the 216 rate net horse power @ 3100 rpm but I know I don't want to run at that speed! 50 mph with stock 5.14 gears on my truck takes 2750 rpm, while it only takes 2450 rpm with the 4.57 gears used in the 3/4 ton. Is 2450rpm a realistic, long life engine speed for a good 216? How about for a 235? That's what I'm trying to figure out.

Planning on 2200 - 2500 rpm seems logical for an ideal cruising rpm for I6 engine longevity, in an empty truck.

I try to put my cruising around my peak tq rpm. Lots of calculators out there to help you figure the right tire, trans gear and diff ratio. On my diesel its 1700 rpm. That's about 60-62 mph and I avg 28mpg highway. 4x4, long bed, lumber rack loaded with steel and 2x material plus roll out box. My 65 c10 I watch my vacuum gauge and cruise at the highest vacuum reading. As for big rpm cruising, if your engine revs to say 5000 and you're cruising at 3000. That's only 60% of total rpms, I don't think it will hurt anything. Maybe Lincoln will chime in, the man is a wizard.

I'll agree with that for a stock 235, maybe a little higher rpm depending on what has been done to the engine. Mine (not stock) does fine at 2700 rpm on the highway, roughly 72 mph in overdrive with 3.90 gears and 30" tires.

My 51 235 sounds and feels happiest in the 2000 to 2500 rpm range, as Hotrod states

I know when I am in the sweet spot in any gear by the sound that it makes, and if I still have acceleration left if I step on the gas a little harder. I don't have a tach, but I do have the seat of my pants.

This was asked a while back and I for got who actually responded and here is their answer.

RPM
2130 comfortably low (fuel efficient)
2500 mid zone
3000 high zone (for cruising)

Thanks everyone for your replies. Consensus is: seat of the pants, 2000-3000 rpm. LOL, that puts me right back to where I started! I think I'm leaning towards the 4:57 rear end gearing and an in-frame refreshed 216. If I'm not happy with that setup I can always yank the 216 and replace it with my good used 235.
Any additional input from actual on the road experience is appreciated!

Jim, I wasn't trying to be glib with my seat of the pants comment. Your best indicator will come from your ear, and what's in the seat of your pants (OK, that was glib).
I can tell you this. You will much appreciate the driveability of your truck with 4.10 vs 5.14 rears, regardless of the 216 or the newer 235.
Carl

Good point Carl, even with no tachometer you can hear and feel when it smooths out and the tone of the engine. It just feels... Right.

Good advice.

I don't know the rpm but the sweet spot on my 49 1/2 ton 3100 is between 40 - 45 MPH. It sounds good, runs smooth and has plenty of power left for the occasional but rare passing. I've run it up to 65 but only held it there long enough to complete the pass. It lets me know me it doesn't like spinning that fast
Engine is a stock 216 & 3 speed tranny, 4.11 gears and 30" tall (R225-16) tires.
There's an rpm calculator somewhere around here that'll give you the rpm based on some specs you enter.

Good luck
Dave

Hey Carl, no offense taken! It's good advice. At this point I'm trying to decide between the 4.11 and the 4.57. 5-6 times a year I need to go to the quarry and pick up a load of rock or cinder and I'd like to be able to use the full capacity of my truck. But I'd be pretty embarrassed to get the truck loaded and then not be able to get it moving! If I'm sure the 4.11 will work OK with a fully loaded truck then that's the way I'll go. Then I just have to find one, not an easy task here in Hawaii! Of course I could always make 2 trips to the quarry instead of one but where's the fun in that?

My experience with both the 216 and the 235 lead me to think the 235 is happy at higher RPMs over longer time than the 216. Both get busy above 2000. But the 216 seems like it is unhappy. The 235 just keeps going. Stock trans, and stock gears in a 3100 will pull more than rated load with no problems. I put a 1/4 yard of sand in it this summer. Whent uphill just fine. Stopping was my biggest concern. It did that rather well. But, I did not go fast for this project was all in town. Might have had new worries if I had hit the highway. But 15-20 miles with a loaded truck was OK. Wish I had some help getting the sand out, but you can't have it all.

194-216-235-261 sweet spot. 2000 rpm
Late 194-230-250-292 sweet spot 2500 rpm. All these 6 cylinder are low rpm torque engines. Many peaking torque at 2000-2500 rpm...some even as low as 1600...such as the old 194 or 216. HP is not what you want to go by...a 292 peaks horse power at 4000 rpm according to factory..so...lets say that 153( 1966 peak net power)...at 2000 rpm you are at literally half that but peak torque..so...75 hp and 260 torque...makes for a great cruising speed...and 2500 rpm means a little more power and your torque unaffected because the stock 292 cam carries its torque for a very short time. Now I'm no specialist on the older 194-216-235-261 engines, but as far as rpm torque peaks they were all very similar....my bone stock 292 with a 600 cfm edelbrock and headers will easily do 4500 rpm...but put it under load and you'll notice how much of a waste of time it is to rev it that high....out of torque, but full power. So...the sweet spot on a 6 cylinder chevy is 2500 rpm. Not matter what year or what cubic inch...they all served one cause...Low RPM torque. So i'd gear yours with a cruising speed of 2000-2500 rpm...my 292 will cruise all day at 2500 rpm...sm420 3.73 gears with a 30 inch tire is about 55-60 miles and hour. But don't put such a tall gear ratio in that your engine will be suffering to accelerate. A 235 is lucky if its making 120 hp and 190 torque. I saw a 235 in a 54 chevy making 97 hp at the wheels....and it was all stock far as I knew. So you might even consider a 261 for a little more power all around. My .02 cents. TJ

RPM Data for Dave's Truck:
2992 RPM @ 65 MPH
2071 RPM @ 45 MPH
1841 RPM @ 40 MPH

John

If your going to spend the money to make a change from the 5:14 do yourself a favor and go with the 4:10. Going to the 4:57 will be such a small change you'll wonder why you bothered. If you have it really loaded up you can use 1st gear to get it moving and you'll be fine.

OK, using Chevy's numbers from the owners manual the 216 shows the net torque pretty flat, from a peak of 168 lbs/ft @1100 rpm, to 164 @2000 and 160 @2400. On my 1 ton dually with 18" wheels (32" tire height) and 4.11 gears, 1950rpm=45mph, 2160=50mph and 2375=55mph. The net horse power at those same speeds come in at 62, 68 and 72 respectively.
I think these are very workable numbers. Again, thanks for all the input!
Now I've got to find that pumpkin!