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Highway speed for a 1939 Olds Series 60


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I am considering the purchase of a 1939 Olds Series 60 that, according to my research, will have a 216 c.i.d. flathead engine.  I asked the present owner if the car could do 60 mph on the interstate as I don't think it is realistic to believe I can always stick to backroads and drive at lower speeds more common in 1939. He said the car will do 60 mph. The engine on this Olds is virtually the same size as in a 1939 Chevy and I have no illusions that a 1939 Chevy will do 60 mph on the interstate. So, is the fella just guessing the Olds will do 60; or is there some extra umph in a flathead engine than in an OHV engine of the same displacement of which I am not aware ?  Any opinions on whether the car will, indeed, be able to maintain 60 mph on the interstate to hopefully keep me from being run over by a semi or a Michigan driver in his 4x4 four door pickup truck doing 85 mph?  Thank you.

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I'm sorry.  I do not know.  Does your '36 Chevy have the standard 4.11 rear end ratio for the year ?

If so, you are really winding out that engine, probably beyond its intended capability.  Trouble is, you can't put an overdrive on the Olds because of the enclosed driveshaft because of rear coil springs. You could put overdrive on your Chevy to save the engine a bit of work. 

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Good point. Maybe we have gotten too used to the low revving modern engines, plus the relative silence of modern cars to think the engine in an old car is revving too high.  On the other hand - since I can't calculate the engine rpm w/o knowing the gear ratios, do you know what your engine revs are at 60 mph?  Thank you for your advice and comments.

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Yes, you are correct. I was thinking I needed the third gear ratio, but it would be 1:1.

 

So, at 60 mph, your Chevy engine is turning about 5000 rpm; your Model A at the same speed is turning about 3600 rpm (shorter ratio; larger tires).

 

That seems like a lot of rpm for those engines.  I think both would be happier at 40 mph and last longer.   I can't find the differential ratio for the '39 Olds, but I don't know why it would be much different than for your Chevy. 

 

So, with the caveat that a flathead engine "might" be more comfortable at higher rpm than is an OHV engine - but no proof of that yet established - I assume the Olds engine would be rotating at the same rpm at 60 mph as your Chevy.  And again, fortunately for you, you can put an overdrive unit on both your cars; but the Olds won't accept an overdrive unit.  So it is, in my view, a 40 mph "cruiser," although capable of 60 mph if needed.

 

Thanks again for your help.

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6 hours ago, BINKYBOY said:

. . . So, at 60 mph, your Chevy engine is turning about 5000 rpm

I'd be very surprised if any 1939 car was turning over 5000 RPM at 60 MPH.

 

6.00-16 tires were pretty standard by then. A 4.11 rear end ratio was mentioned above, which also is pretty standard for the era. My road speed calculator on my “How Fast Should I Drive” page shows 3000 RPM to be 61 MPH for that combination.

 

I don't know the specifics of an Oldsmobile engine of that era, but if it has full pressure lubrication and is reasonably well balanced could probably cruise at that speed when new. Of course it is no longer new and standards of repair and restoration vary. But assuming that it has a mechanically sound drivetrain, brakes, and suspension it should be able to drive at 60 MPH.

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Sorry, Gents, I've been away for a bit.  To answer JFranklin, I used ~63,000 inches/mile divided by the circumference of a 17" tire (which is approx 53") to determine ~1200 revolutions of the tire per mile. Then I multiplied the axle ratio - 4.11 - times the number of revolutions of the tire to get ~5000 rpm.  I can skip the speed adjustment b/c 60 mph is 1 mile per minute.  I am assuming, as stated above, that the third gear ratio is 1:1, which apparently ply33 agrees with, as he does the same calculation in his article.

 

To respond to ply33, I can't seem to use the speed calculator embedded in your article b/c it is automatically set to 4.375:1 differential, which means that a calculation using a 17" D tire indicates 38 mph.  Applying a factor of 0.63 (38 mph/60 mph) to my 5000 rpm calculation to adjust for lower speed still gives me 3100 rpm as the engine speed using the 4.11:1 Chevy differential ratio.

 

With regard to your comments about the 1939 Olds I am looking at, wheel size and differential ratio are essentially the same as the 1936 Chevy, except the tires are 16" instead of 17" meaning the engine is revving even faster on the Olds than the Chevy at the same road speed.  The good news is that the Olds has less than 8000 miles on it; it does have four main bearings and it does have full forced lubrication.  However it is an L head engine, whereas the Chevy engine is OHV.   I don't know if an L head engine is capable of more RPM than an OHV engine of that era.  Since your engine, ply33, is also an L head, perhaps you have a comment on that question.

 

So I guess if a 1936 or 1939 engine is even capable of 5000 rpm w/o destroying itself, the cars CAN attain a speed of 60 mph - you just better not do it for long periods of time - which is my question.

 

Either JFranklin or ply33, or anyone else, please let me know where I have made a mistake in my method of calculation.  I'm willing to admit I'm wrong if that is the case. Just don't tell my wife I made a mistake. She thinks I'm perfect.   Thank you one and all for your thoughts and contributions.

 

[note to ply33: I own the complete set of fiberglass molds formerly used by Redneck Street Rods of Evansville, IN, to build an entire, unmodified 1933 Plymouth PD coupe. It is the only complete set of molds I know of in the U.S. for that model, as original. As you may know, Redneck SR built many 1933 Plymouth PD coupe bodies that won various awards at street rod shows across the US.

 

My molds are placed with Toledo Custom Fiberglass (TCF) in Toledo, OH, for the production of any, or all, of the parts.  I know it ain't the real steel; but sometimes you have to use fiberglass to repair, build, or modify your 1933 PD Plymouth - especially since so many 1933 Plymouths were beaten up in track racing in the 1940s and 50s. I even have a set of molds to build 2" wider rear fenders to accept a wider tire, along with modified running boards that connect the front fender and the wider rear fender smoothly.

 

Please contact TCF if you or anyone you know is in need of body parts for their 1933 Plymouth PD. You can find TCF on Facebook with their contact information and some photos of their work.]

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On my calculator you can enter any rear end ratio you want. If you know the mounted tire diameter, usually available on the tire manufacturer's website, you can enter that. If you don't know the mounted tire diameter then you can enter the wheel diameter and tire cross section to get an estimate. The calculator assumes a typical cross section for that era.

 

In you calculations you seem to be using the wheel diameter rather than the tire diameter. For example, the mounted tire diameter for my 5.50-17 tires (something close to 28.11") is very close the the same as for a 6.00-16 (something close to 28.12") yet you are indicating a significant difference between the circumference of the 16 and 17 inch wheels.

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The McCullough Formula for Determining RPM and Engine Speed

The McCullough Formula provides a method for calculating the speed of an automobile for a given engine RPM. By adapting the formula, engine RPM for a given road speed can also be calculated.

For accuracy, it is essential to measure the diameter (in inches) of a rear tire (front tire for a front wheel drive car) [edit: with the weight of the car resting on the tire]. Do not rely on the published diameter of a tire as this may be a bit inaccurate. Reference below to “high gear” assumes direct drive through the transmission (1:1).

Using the two formulas below, a small table can be constructed giving either speed for a given RPM or engine RPM for a given speed for a particular vehicle. The table can be carried in the car as a reference.

McCullough Constant: .002975

To Solve for Speed for a given RPM

                                    Tire Diameter (inches) x Engine RPM x .002975

MPH (high gear) = —————————————————————

Rear Axle Ratio

 

To Solve for Engine RPM for a given speed

MPH (high gear) x Gear Ratio

Engine RPM = ———————————————

Tire Diameter (inches) x .002975

 

References: Dyke’s Automobile & Gasoline Engine Encyclopedia

(1923, 1924 & 1943 Editions, Page 1046).

 

 

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16 hours ago, EmTee said:

Ask the seller how long it takes the car to come to a stop from 60 mph.  ;)

It will stop when it hits a tree, bridge abutment or guard rail.  Isn't that why they are there ? 

 

Your point is well taken, Sir.  Good information about stopping distance in ply33's linked article.

Thanks for the reminder.  Cheers.

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17 hours ago, Grimy said:

The McCullough Formula for Determining RPM and Engine Speed

 

The McCullough Formula provides a method for calculating the speed of an automobile for a given engine RPM. By adapting the formula, engine RPM for a given road speed can also be calculated.

 

For accuracy, it is essential to measure the diameter (in inches) of a rear tire (front tire for a front wheel drive car) [edit: with the weight of the car resting on the tire]. Do not rely on the published diameter of a tire as this may be a bit inaccurate. Reference below to “high gear” assumes direct drive through the transmission (1:1).

 

Using the two formulas below, a small table can be constructed giving either speed for a given RPM or engine RPM for a given speed for a particular vehicle. The table can be carried in the car as a reference.

 

McCullough Constant: .002975

 

To Solve for Speed for a given RPM

 

                                    Tire Diameter (inches) x Engine RPM x .002975

 

MPH (high gear) = —————————————————————

 

Rear Axle Ratio

 

 

 

To Solve for Engine RPM for a given speed

 

MPH (high gear) x Gear Ratio

 

Engine RPM = ———————————————

 

Tire Diameter (inches) x .002975

 

 

 

References: Dyke’s Automobile & Gasoline Engine Encyclopedia

 

(1923, 1924 & 1943 Editions, Page 1046).

 

 

 

You're the best, Grimy.  Always watching; always helping. You have provided me with valuable advice and observations before on other vehicles.  How is the 1918 P-A running ?  Cheers

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23 hours ago, ply33 said:

On my calculator you can enter any rear end ratio you want. If you know the mounted tire diameter, usually available on the tire manufacturer's website, you can enter that. If you don't know the mounted tire diameter then you can enter the wheel diameter and tire cross section to get an estimate. The calculator assumes a typical cross section for that era.

 

In you calculations you seem to be using the wheel diameter rather than the tire diameter. For example, the mounted tire diameter for my 5.50-17 tires (something close to 28.11") is very close the the same as for a 6.00-16 (something close to 28.12") yet you are indicating a significant difference between the circumference of the 16 and 17 inch wheels.

You are correct and pointed out my dumb error.  The correct answer according to Grimy's handy-dandy formulae appears to be just under 3000 rpm.  Much better than 5 grand.   🤪

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2 minutes ago, BINKYBOY said:

You're the best, Grimy.  Always watching; always helping. You have provided me with valuable advice and observations before on other vehicles.  How is the 1918 P-A running ?  Cheers

Thank you!  Just brought the 1918 over to the house for a little routine maintenance and cleaning before tomorrow's Fathers Day car show at the Blackhawk Museum, 25 miles from here.  We ran it on a four-day HCCA tour out of Paso Robles CA in early May, enjoying the magnificent back roads, some of which had oak trees forming an arbor over the road for 1/4-mile stretches.

 

By the way, for these L-head undersquare (long stroke) engines, I want to cruise at no more than 70-75% of redline rpm (if published) or the rpm at which advertised max hp is obtained.  My MoToR manual shows 1939 Olds 60 is rated 90 hp at 3200 rpm.  So that would be 2240-2400 rpm for that Olds engine.  I think 4.11 is a safe estimate for differential ratio.

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8 minutes ago, Grimy said:

Thank you!  Just brought the 1918 over to the house for a little routine maintenance and cleaning before tomorrow's Fathers Day car show at the Blackhawk Museum, 25 miles from here.  We ran it on a four-day HCCA tour out of Paso Robles CA in early May, enjoying the magnificent back roads, some of which had oak trees forming an arbor over the road for 1/4-mile stretches.

 

By the way, for these L-head undersquare (long stroke) engines, I want to cruise at no more than 70-75% of redline rpm (if published) or the rpm at which advertised max hp is obtained.  My MoToR manual shows 1939 Olds 60 is rated 90 hp at 3200 rpm.  So that would be 2240-2400 rpm for that Olds engine.  I think 4.11 is a safe estimate for differential ratio.

A slightly different question for you, Grimy:  Is it any "safer" so to speak, to cruise at a higher rpm if the engine has more main bearings than cylinders?  Example: some Nashes; some Grahams; all Pierce Arrows ?  Big assumptions being full pressure lubrication, good condition bearings, great maintenance... in other words, an almost perfect world.  Thank you.

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12 minutes ago, BINKYBOY said:

A slightly different question for you, Grimy:  Is it any "safer" so to speak, to cruise at a higher rpm if the engine has more main bearings than cylinders?  Example: some Nashes; some Grahams; all Pierce Arrows ?  Big assumptions being full pressure lubrication, good condition bearings, great maintenance... in other words, an almost perfect world.  Thank you.

I *think* yes, but I will repeat @edinmass admonition today in another thread to pull the pan, check condition of at least couple of the rod bearings, and clean out oil pump and any accessible galleries as the first, or near-first, task of any new acquisition if you're not very familiar with its maintenance regimen and performance over years.  The latter caveat reflects that I did not pull the pan on my 1918 because I knew the car and its owner for 18 years.

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18 hours ago, Grimy said:

So that would be 2240-2400 rpm for that Olds engine.  I think 4.11 is a safe estimate for differential ratio.

This is probably a good estimate, but I will say that my experience has been that the car will tell you when you're pushing too hard.  Not scientific, but if you hear the engine droning, feel harshness or vibration through the steering wheel and find yourself making continuous corrections to steering and accelerator, you're probably forcing the situation...

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