SAFE RPMS

[Ben Bruce aka First Born]

 Dave, perhaps I sounded argumentative, I probably mis-interpeted your thoughts. Just did not want new, younger guys and gals to get a wrong impression.

 

  Probably the longest trip we took in those days was 1954. My 1940 41D and Dads 1941 41D. From Joplin, Mo to Duncan, AZ and return. LOADED. Six people in each. 

 

  Like you, I prefer the RPM's lower. I have a 3.36 [3.4] in my 1950 41D.  Dropped the third gear reves by about 700 versus the 4.10. I just find nothing to indicate the Buick engineers thought the mid 3000 rpm's were too high. The shop manual even has a 70 mph column in the gas mileage test. At least in my 1950 manual. I confess I have seen no manual for a 1938-1940.

 

 

  Ben

[Janousek]

A little more from the 48' specifications book.

 

248 engine  in a 40 series 

 

110hp @ 3600 rpm

206 tq @ 2000 rpm

 

Now Dave is very conservative running his car at the 2200 rpm mark.  Should last forever at those rpm's but if you read into the specs the engine is surely designed for more RPM's.  

 

If I ever get around to my 48' I'll know in a hurry because I'll drive it like I stole it.  I've gotta get a tach on our 31' and pull the rear cover and see what ratio is in it.  That thing at 60 is smooth and acts like it's loafing along.  

[LAS VEGAS DAVE]

Usually the maximum horsepower of any engine is right near its redline and the maximum torque figure is where an engine is in its sweet spot. When racing you wind up the motor to its maximum horsepower or slightly above and then shift but that's not the rpms you would cruise at.  The highest torque rpm would be the best place to cruise at if possible. A couple of hundred rpms on each side of that figure would be ideal. In 1938 there were very few roads that a car could go 60 mph steadily on and there were very few cars that could do it. In 1953 if you could drive 65 mph you were hauling ass. Today 80 mph is the flow of traffic out here in the western states on the open roads and all new cars can cruise at that easily.

Edited October 15, 2015 by LAS VEGAS DAVE (see edit history)

[jenz38]

Great conversation here, i like it when the old guy talk from the ol days...

The Centurys has indeed the 3.9 ratio but they have as only model 15" wheels.

I think if you can grab a (rare) century rear end and drive it with our 16" wheels, the rpm would lower than with the oem wheels.

In my case i drive in rear 7.50-16 Rubber,because of that increase my speed to 5 mph at the same rpm.

Ok the tail comes up a lil bit on my (stripped) coupe ,but for me its ok because of 'form follows function'

[jenz38]

[jeff]

Good point on the wheel diameter - that (actually, radius of wheel plus tire) needs to be in the spreadsheet when calculating rpms.

 

Remember, the 105hp of the prewar Buick 248 can only live with so much gearing.  4.44 would minimize downshifting, 3.90 would be just a little bit better at speed, 3.60 must have been reasonable, since the semi-automatics lived with it.  (but I guess they would kick down from 4th to 3rd automatically???)  Don't get too enamored with any lower (numerical) ratios, because you need more engine to live with the taller gears.  You don't want to get into a situation where the car looses speed on the slightest hill, and has to be downshifted to second too often.

 

I like to think about how things were back when these cars were new.  Imagine - your impressions would largely be based on what you traded in.  Had you been living with a '31 Model A sedan or a '34 Chevy, you would be AMAZED

[jeff]

... AMAZED by the performance of the new '38 Special.  "how little shifting is required!", "how smooth and quiet  - even at 50 mph!!"  These impressions were all relative to the standards of the time.

 

(no offense intended to Model A and '34 Chevy owners - two great old cars!)

[C Carl]

I like to answer the inevitable question "how fast will it go" regarding my mid '20s Cadillacs : " Almost twice as fast as any sane person ought to drive 'em". I then tell the curious that the fortunate original owner had most likely lived at least 1/2 his , or her life in horse drawn days ! Might not have seen a car until in his/her '30s ! Imagine ! Do any of you know how far down the line a pair of steeds could have drawn a 4 passenger carriage over decent flat roads in an hour or two ? And now comes a mid '20s car which will cruise all day at 35 !!! WOW !!! And do it up hill and down ! Perhaps without downshifting ! And if going long distance , no swapping the ponys out ! Yeah, my old iron does not have the handling to cope with an emergency at pedal to the metal speed. Was never intended to be driven at 55 all day. Just like your modern car is capable of highly illegal speeds , doesn't mean you should drive it all day at 140. Right ? - Carl

[27donb]

Just like your modern car is capable of highly illegal speeds , doesn't mean you should drive it all day at 140. Right ? - Carl

 

My point exactly.

 

Just because you could, does that mean you should?

[LAS VEGAS DAVE]

What I was looking for was a way to be able to cruise along at 60 miles per hour with the engine thinking its going 40 miles per hour and yet to keep the performance and hill climbing ability of the car with stock gears using the original motor which only had about a hundred horsepower. I don't think there is any way to do ALL of that except with an overdrive, with any other method there is a compromise in one of those expectations.  Sixty miles per hour is not to fast for these cars and they can be driven like that with out any strain on the rest of the components all day if need be. Back when they were new there was no need for a car to cruise at sixty miles per hour, much more important to have enough power to be able to climb hills. Its just fun trying to do what ever we can to keep these old cars running decent and experiencing the joy of driving them. 

[jeff]

Dave,

 

I totally agree with you.  For me, these side-bar conversations are just interesting head scratchers.  (what could it do, should it do, etc.)

 

Overdrive is most certainly the best solution.  Although I love my old Buick, I also love the independent makes for their adoption of OD.  For me, and my wallet, the custom overdrive probably won't happen.  That's why a 3.9 ratio would at least be a step in the right direction.  I have a friend with a '39 Packard Six, and, although it didn't have overdrive, he was able to easily get all the parts and pieces and make a conversion.  Wish the Buick offered the same option. 

 

So, a hearty endorsement from me on your OD project, and also for your reasoning.  You basically want to go just a little bit faster, while dropping the RPMs a bunch.  I'm fully on board.

 

Jeff

[Daves1940Buick56S]

Just a data point - I now have a 3.41 rear on my '40 with the 248 engine and so far no issues with downshifting on hills. I went up and down Bear's Den mountain west of here at 55 mph at 2500 rpm with no problem. Unfortunately the gears are roached and I will have to find another pumpkin but that's a different problem!! 

 

Cheers, Dave

[1967 - 1997 Riviera]

I've thoroughly enjoyed all the information exchanged in this discussion, and find all the viewpoints expressed useful.

 

For a little different take on the O.D. issue, let me relate how a modern Buick, the last generation of Rivieras (1995-1999), perform with their factory installed, 5th speed overdrive transmission. With the cruise control set at 71-72 miles per hour while going steady-state along a flat, straight interstate, the tachometer is right on 1900 rpm. When you need a burst of acceleration, not wide open throttle, to pass another vehicle, the transmission will downshift to 4th speed and the engine rpm increases to anywhere from 2200 to 2600 rpm, depending on throttle position. When you let off the gas pedal, it upshifts to O.D. and goes back to 1900 rpm. Peak torque of the 3.8 supercharged engine is right about 2,400 rpm, so a demand for acceleration puts you right in the engine's torque sweet spot. Thereby, I think that an OD-equipped 38 Buick at 2,000 to 2,200 rpm for highway cruising is just about right. And keeping the original 4.44 or 4.1 rear axle ratio for extra around town driving "grunt" is a plus.

 

My 2 cents is that overdrive is the way to go. Less engine stress, lower fuel and oil consumption, longer engine life and a lower level of driveline noise. Just be sure to keep, or even upgrade, the brakes, suspension and tires as best as you can.

[LAS VEGAS DAVE]

Realistically there are many things in the old car hobby as well as the rest of life that require a compromise. Gearing our old cars is full of compromise's. A modern car has a four, five, or six speed transmission, wether it's a standard or an automatic. The engines have plenty of power and its damn near impossible to overheat them. They will go a hundred thousand miles, a hundred miles per hour, and stop in a blink of the eye. Computers control the engine, transmission and even the brakes. They are great for getting from A to B and they don't use much gas. They all look alike, aren't much fun to drive and and have no soul. It's fun to try to keep our old cars running well and its fun trying to make them fit into todays world. Changing the gearing is one way to make them fit into todays world a little better but in reality they'll always be from a different era and they'll feel like that whenever we drive them, that's just one of the best part of  owning one. 

Edited October 17, 2015 by LAS VEGAS DAVE (see edit history)

[hidden_hunter]

Interestingly the local advertising material here for the 26 model stated that it was 75HP and 75MPH, with the stock gearing is it even possible to get it to 75mph - short of driving it off a cliff? 

[Janousek]

I like the overdrive.  I've driven packards with them and they are neat.  Gear vendors have a nice (smaller sized) overdrive but you need 12 volts to run it.  It is more money than a used borg warner though.  Normally don't see a need 12 volt conversions but it can be done without anybody noticing.  

 

I also like to use 1st gear and those cars with 4.4 really don't have a usefull 1st gear.  We always started out in 2nd in the 40' special.  

 

I really like both ideas and I've been ponding setting our 48' up with overdrive with a 3.90 if I can find one.  Or have a 3.42 built and go from there.  These engines have the torque to run lower gear ratios.  

 

Our Auburn has a 2speed columbia rear end that was supposed to be more usefull in the power ranges.  When in low range it's pretty useless unless you like driving 30mph in high gear with the engine screaming.  

[C Carl]

Heard rumor there was a '26 Bently parked outside an automotive function I attended today. Now this Speed 6 flat rolls! Pilot says 90 - 95 is no problem. Loafs at around 2000 rpm at 70. Said to be very stable, and has very good rod actuated , power assisted huge brakes. Wish I could give you first hand driving impressions ! - Carl

[nzcarnerd]

It is Bentley with an extra 'e'.  Remember that this car has a 6 1/2 litre (almost 400 cid) engine with an overhead camshaft and four valves per cylinder.  It also has a non detachable cylinder head.  It is probably worth more than 10 times what the very best pre war Buick is. It is a very big car though, with a wheelbase longer than any Buick of the pre WW 2 era, and at a guess weighs over 4,000 lb even with that minimalist body.

[Buicknutty]

 Nice discussion.

 I have a '41 Roadmaster Coupe, rebuilt with more compression and insert bearings, but otherwise a stock 320, but I am now likely in the 170-175 HP range and 280+lb ft of torque, in a 4,200 lb car.

It has the, stock for this model, 3.9 gears, and I have a 3.4 to go in, but I haven't done it yet. I agree that an overdrive unit would give the best of both worlds, but it is quite expensive, esp. paying in US dollars at the current exchange rate, so I will go for the rear gearing change next year. With the torque and HP of this engine, it should still have lots of pulling power with the taller gearing.

 I had to have my speedometer rebuilt earlier this year, and it is now quite accurate. We recently did a long weekend's worth of touring with the '41, with one leg a 200+ mile stint on a major highway, at 65+ MPH, not sure what revs this is, but likely in the 2200-2500 RPM range. 70 is my self imposed speed limit in this car, it feels like it has lots left at this speed, but I too am concerned about spinning it too fast for too long. To use that old expression, "back in the day", I would of run this car way faster then, but not now, I've seen too much of what can go wrong!

 Keith

[LAS VEGAS DAVE]

Kieth, your engine is turning 2839 rpm ay 65 mph with 3.9 rear axle, at 70 mph it will be 3058 rpm. This is calculated with a 30 inch diameter tire. Normally they are slightly less than that which means the rpm would be a little higher. If you install the 3.4 ring and pinion your rpm would be 2465 rpm at 60 mph and 2666 rpm at 70 mph.

[Guest Straight eight]

Hey Guys, I have a 47 56C that runs 160 degrees since I added Red Lines  "Water Wetter"

 

This stuff  comes in a bottle of 12 oz, and makes the water more efficient so the water absorbs the heat better by disposing of air bubbles.

 

I've been using it for several years, and it really works.  Mfgd by RED LINE. a well known supplier in the auto parts business.

 

Would like to hear from others who have used it.

Edited October 22, 2015 by Straight eight (see edit history)

[C Carl]

In spite of the fact that no one asked me what was going on inside VRM where the 1926 Speed Six Bentley dropped in , I was greeted by this contemporary to the Six (see posting 57 above) as I walked through the door. Unless requested not to , I will put up a few more pics in the near future. For your enjoyment , 1927 S :

[Buicknutty]

 Re: Water Wetter, personally, I have not used it, but a few friends of mine have, and they say that it helps their engine run cooler.

 Keith

[Larry Schramm]

IMO, if the car is overheating, there are other problems that are being covered up with the additive. I am not that old, but I do not believe that those additives were required when the old car was new to run properly.   Just IMO

[LAS VEGAS DAVE]

  The cooling systems at least on the 37 and 38 Specials needs to be in top notch condition if it is to work well at temps in the nineties or over a hundred. At those temperatures long hills or long times idling in traffic at lights and then not moving very far before another light forces you to idle again and so on can cause even the best systems to reach their limits. I find that even in the high nineties or temps over a hundred if the car can just keep moving even at 30 miles per hour the temperature will stay 180 or less.  If the outside temps are in the eighties my cooling system works fine even in traffic. If the temps are in the seventies or less the car mostly runs at 160 degrees and not higher than 180 degrees. In my view a good modification that would improve cooling considerably would be a custom fan shroud. Another help would be louvers in the hood as the engine compartment seems to trap heat extremely well. I won't do either of those to my car as I enjoy the challenge of keeping it original and dealing with whatever its problems are. I live in Las Vegas and during the summer its one of the hottest places in the United States, sometimes its just better to drive something else in the extremes. At this time of year its either beautiful out or its cold so the old Buick can be driven whenever I want with no concern at all about the water temperature. I have an electric heater that sticks onto the oil pan by magnetics that I will be using soon for the cold mornings. My idea of cold (40 degrees or less) is not at all like some of you guys but I like the oil to be warm when the car firs starts on a cold morning to help lubricate everything. 

[Guest Straight eight]

Speaking about efficiency, that's all the Water Wetter does, is remove the air bubbles so the water can do its job effectively.