SAFE RPMS

[LAS VEGAS DAVE]

I have a question concerning the rpms of the 248 cu inch 8 cylinder engine as is found in the 37 or 38 Buick Specials.  What is considered a good and safe CONSTANT rpm that these engines can cruise at on a long trip? 

 

Below are the rpms the engine would be turning at different speeds with a stock 4.44 rear axle ratio and with an overdrive. The calculations use a 28.5 inch tire diameter which is what my tires are on the stock 16 inch rims.

 

 STOCK 4.44 REAR AXLE RATIO         OVERDRIVE (3.10 RATIO)

 

     40 MPH = 2094 RPM                          40 MPH = 1462 RPM

     45 MPH = 2356 RPM                          45 MPH = 1645 RPM

     50 MPH = 2617 RPM                          50 MPH = 1827 RPM

     55 MPH = 2879 RPM                          55 MPH = 2010 RPM

     60 MPH = 3141 RPM                          60 MPH = 2193 RPM

     65 MPH = 3402 RPM                          65 MPH = 2376 RPM

     70 MPH = 3664 RPM                          70 MPH = 2558 RPM

     75 MPH = 3926 RPM                          75 MPH = 2741 RPM

 

I have always thought a comfortable rpm for most engines is between 2000 and 2500 rpm if its for a long steady speed, what are your thoughts?

Edited October 8, 2015 by LAS VEGAS DAVE (see edit history)

[Mark Shaw]

In my opinion, 2000 - 2200 RPM

[jvelde]

I too have 16 inch rims, but my bias ply tire diameter is at most 28.5 - what make and type of tires are you running that are 30 inches?

Thanks, JV

[27donb]

In my opinion, 2000 - 2200 RPM

 

The voice of reason!

 

With all the talk of "pushing" old Buicks to highway speeds...I couldn't agree more with Mr. Shaw's opinion.

 

My Grandfather's 1924 Model 45...my Father's 1927 Model 54CC...both 6 cylinders...never, ever an engine problem or issue keeping the engine RPM's low.  Those engines ran cool and forever.

 

I don't know how different the old sixes from the 1920's are from the eights of the 1930's, but slow and steady is preferable in my opinion.

[LAS VEGAS DAVE]

I too have 16 inch rims, but my bias ply tire diameter is at most 28.5 - what make and type of tires are you running that are 30 inches?

Thanks, JV

 

YOU ARE RIGHT AND I MEASURED WRONG, 28.5 INCHES IS CORRECT, I WILL REDO THE RPM AND SPEED CHART TO REFLECT THE CORRECT DIAMETER, THANKS FOR CATCHING THIS.

[Matt Harwood]

Also remember that just because you can go 75 MPH without over-working the engine doesn't mean you should. You're still driving on 80-year-old technology, ancient brakes, and a 1930s suspension. My overdriven 1929 Cadillac is happy at about 52, which doesn't stress the engine and still puts me within what I feel are safe parameters for the old suspension and brakes. The engine will easily push it to 60-65 (which is only 2000-2300 RPM), but there's no way I feel safe at those speeds. Your Buick is obviously a lot more capable but it's still not as good as a modern car, not by a long shot and those speeds are going to put you in fast company in traffic. At least with my slow car, folks give me a wide berth.

 

So just because the overdrive means less stress on the engine, don't forget that the greater speeds are putting more stress on wheel bearings, hubs, spindles, brakes, steering, suspension, and tires, and none of it was designed for sustained high-speed travel on today's interstates. I'd say 60 MPH, maybe 65, should be your reasonable limit regardless of how easy it is for the engine to push it faster.

Edited October 7, 2015 by Matt Harwood (see edit history)

[27donb]

Also I've found the front and rear wheel hubs reasonably "warm" after returning from short trips at realistic speeds, meaning to me that there is more friction involved in the old style bearings.  The transmission really warms up too after being out on the road for a while.  Greater speeds only mean more heat and stress, as others have said.

 

These cars are not lightweights by any standard, so the faster you go the harder it is on the binders as well.

 

My 27-25 Standard is comfortable at 35 mph, the 27-54CC Master is happy at 40 - 45 mph max speeds.

Edited October 7, 2015 by 27donb (see edit history)

[Ben Bruce aka First Born]

 Dave, our family had a '38,  two, '39s, a '40 [my first Buick, in 1953]  and a '41. The '38 was bought in Dec 1949.  We lived in Missouri, where the speed limit back then was "reasonable and prudent. Dad drove his cars at 60-65 on the hwy. I drove my '40 at LEAST that fast then. Dads '41 ran well at 60-70. So I see no problem with the engines running high 20s to mid 30s. Sure, it sounds fast. But that is the way they were designed. 

 

  Later, I had a '50 Super. I guaranteee it ran 70+ a LOT.  My , '48 was real comfortable at 70.All day.

 

   I believe we have become spoiled with our low rpm engines today. 

 

  Ben

[LAS VEGAS DAVE]

I dont worry much about the suspension or wheel bearings. I think the frame and suspension are plenty beefy and the wheel bearings if lubed properly are also fine. The brakes are just fair at best, you must drive with much more space in front of you than in a new car with ABS and disc brakes. The engines are the weak link in my opinion and should be treated as such. I think 60 mph with an overdrive at 2200 rpm is a good continuous top speed if driving the car on a freeway. My car seems to like it there so thats where I drive it when on the freeway. When the car had the stock 4.44 ratio that was only about 43 mph so I guess back in the day that was the speed they drove if the roads were good. I had a bone stock 33 Ford for some years and it was good for a higher cruising speed than that and it had a 4.11 rear end with a little 239 cu inch flathead V8. It had much worse brakes than the Buick and they were mechanical not hydraulic. In any case 60 mph today on a freeway is right hand lane only stuff and still slower than most anything else goes. The best way to go somewhere in the pre war Buicks in my opinion is to take smaller hiways whenever possible. 

[suchan]

I had a 38-41 I bought from a mechanic who was noted for taking the car on long trips, and driving it at 60-65 MPH, including a meandering 6000 mile trip to the St Louis BCA national in the '90's. Those are definitely slow-lane speeds on the freeway, but I can't see the point of driving an old car on the freeway if you can avoid it.

Some Buicks sound  like they're about to fly apart at those speeds, but this one seemed to settle into a groove at around 60, and actually got quieter. But as mentioned above, it's not just the engine that's stressed by high speeds (the engine might be your least concern), so let common sense determine your cruising speed.

[LAS VEGAS DAVE]

I had a 38-41 I bought from a mechanic who was noted for taking the car on long trips, and driving it at 60-65 MPH, including a meandering 6000 mile trip to the St Louis BCA national in the '90's. Those are definitely slow-lane speeds on the freeway, but I can't see the point of driving an old car on the freeway if you can avoid it.

Some Buicks sound  like they're about to fly apart at those speeds, but this one seemed to settle into a groove at around 60, and actually got quieter. But as mentioned above, it's not just the engine that's stressed by high speeds (the engine might be your least concern), so let common sense determine your cruising speed.

I also think its best to avoid the freeways whenever possible. The problem here in Las Vegas is the roads have many stoplights placed not very far from each other, the lights take long times before changing so if its hot out which it is in Vegas 4 months a year the old car starts to go over 180 just as the light turns green. As you approach the next red light the temp has dropped below 180 but then you sit again at the light and it starts all over again. The freeways allow you to go across town without the lights and the car doesn't care how hot it is in the sun because it is moving and it runs under 180. I love it at night because its usually only 80 degrees instead of 100 so the lights don't matter to much. In another two weeks the temp will only be in the eighties during the day and the seventies at night so it won't matter when or where the car is driven. Today a friend and I drove about 70 miles in the old Buick to go loo at an old Ford someone has for sale. The Buick ran great never going over 180 degrees. 

[FLYER15015]

Dave,

Now you know that a car like yours is meant for cruzing the strip, not for blasting down I-15, don't you.

Mike in Colorado

[LAS VEGAS DAVE]

Dave,

Now you know that a car like yours is meant for cruzing the strip, not for blasting down I-15, don't you.

Mike in Colorado

Mike I live here so I hardly ever go to the strip unless friends are visiting, then they make me go. I can't really equate 60 mph as BLASTING down the I-15 but I must admit that there is something in me that says "wow you're on the freeway with the old Buick and its humming right along."  It just seems amazing to me that its probably the oldest car on the I-15 within hundreds of miles and its doing just fine. I feel like it just wants to keep going to some far off place so that I can say "it made it." I've already driven it all over Las Vegas and around the Lake Mead National Park several times, it needs to go to Utah or maybe Prescott Arizona or Los Angeles or maybe up by you in Colorado but its yearning for a road trip. My girlfriend will be back here in December so next year I'm sure some sort of trip will be in store for us. Until then there is one more spot not to far from here but with a mountain to climb as a good test for the 38, its called Mt Charleston and it goes up into the pine trees and has snow there about a third of the year. I may try that trip next week, if it climbs that grade alright then It should be able to go anywhere. Its a long long uphill grade and should be a good test of the cooling system and show any other problems if there are any. Whenever I go it will be during a weekday morning as there will be no tourist traffic at that time and I won't be holding anybody else up on the mostly two lane road. Sorry for the rambling. 

[jeff]

It will be interesting to hear about the performance up the long grade.  The only downside to the higher gearing of the OD is that you still only have a little better than 100 hp.  So, will you need to kick it out of OD and take the hill at 45 - 50?  Or, with enough speed, will the engine pull the grade in OD?  That will be a great test.

 

My '38 with stock 4.44 gearing is very happy at 40 - 45 mph.  It will do 55+, but it doesn't sound like it is happy about it.  Probably more about my sensitivity - the car can probably do it all day long.  Bottom line, I concur with your thoughts on 2000 to 2200 being a good range - age considered.  No doubt the cars are capable of more. 

 

Interested in your comments about the car heating up when at a light, or slow traffic, then cooling back down with enough road speed.  I just had my radiator cored, and this describes my condition as well.  I would feel better about it if the engine temp dropped down as it idled (less work, still circulating coolant), but this does not seem to be the case.  Is this to be expected of these cars?

[Ben Bruce aka First Born]

 Guys, they should be running 180 degrees all the time. I believe a 180 thermostat was called for. This being the case, cooling BELOW 180 is the "problem".

 

  Ben

[jeff]

Hmmm.  My '38 Special definitely warms up as speed decreases.  Runs at about 180 - 185 otherwise, but climbs a bit at stop lights or extended low speed travel (<10 mph).  My thermostat is a NOS Harrison (old type) which checked exactly to the book - begins cracking open at about 150 and is fully open at 170.  Just like the '38 shop manual calls for.  Block extensively flushed, bypass works fine, pump flow checked by running it briefly into a bucket.  By the way, I should have said that my radiator was "rodded-out" not cored.  I found an old school guy in Wilmington, OH who still does it.

 

After a lot of thought and analysis, it just seems to me that the water flow at idle to cylinder number 8 is just not quite optimal.  (I suppose I may still have some encrusted junk around the area of the sensor)  I like my friend's Dodge engine and another friend's Packard - they have a water distribution tube.  In the Buick, the water that finally gets to number eight can't possible be the same temperature as when it passed by number one! 

 

Either this water flow theory, or insufficient air flow at low speeds.  By the way, Ben, I have a 1950 fan in my garage - it has much broader blades, set at a more aggressive angle than does the '38.  I was going to try it, until I realized the pulley sizes were different too - looks like they made the fan much more aggressive, but slowed it down a bit.  So, putting on a '38 with my pulleys would have it running too fast at 50 mph (I suspect).  So, I haven't tried that yet.

 

I am going to play around with an infrared thermometer a bit more this weekend.

 

Thanks for the comments - hope this isn't off topic.

 

Jeff

[LAS VEGAS DAVE]

I like the discussion about the water temps. Jeff and Ben I have always liked 180 as the perfect temp in all the old cars I ever owned. If they ran at 180 we were happy. My 38 Buick owners manual states that 160 to 180 is ideal and that 190 is fine if it is extremely hot weather, it does not say what temperature extremely hot weather is. If it is below 75F outside the car runs below 180 all the time, between 160 to 175, I like that because at a light it can go to 180 which is fine. The problem with my old car is that unless it is in the sixties outside, if the car idles it will slowly get hotter and hotter. If its in the sixties like sometimes it is at night it can idle for hours and it wont get over 180. Here in Vegas the days are still in the eighties so long lights make me nervous. Sometimes an ambulance comes and triggers the light and then they last twice as long. If its in the eighties outside the car will then creep to 180 plus before the traffic moves again, there is not much more of a window before the temps could go to 190 or above . If its in the eighties outside the car will then creep to 180 plus before the traffic moves again, there is not much more of a window before the temps could go to 190 or above . Also if the traffic is heavy it doesn't move very fast and stops often, it makes me nervous. By the end of this month it will start to drastically drop in daytime temps so it will be more pleasant to drive in the daytime once again. I drive the car pretty much every day. When I got the car it had only 18000 plus miles on it but I'm 73 and I decided to drive it till I can't instead of saving it as a low mileage car for someone else after I'm gone. Jeff as far as the hill going up to Mt Charleston goes I think I will be in second gear overdrive or third gear regular not overdrive. The overdrive gives me many options and makes driving the car really fun. In my opinion the best modification a guy can ever make to a 38 SPECIAL is add an overdrive. Its a pain in the a-- but it can be done in the driveway and its pretty straight forward. Maybe the Century or Roadmaster with the bigger engines and the higher gear ratio rear ends those models have an overdrive is not a big deal but in a SPECIAL it changes the whole driving experience. I put a 3.54 ring and pinion in a 1933 Ford rear end many years ago to make it higher geared but an overdrive is a much better option. I think I'll ride my motorcycle up to Mt Charleston first to get it fresh in my mind exactly how steep and long it is since I haven't been up there for a few years. Maybe I'll do that this weekend. As I drive the old Buick to breakfast every morning and then to what ever errands I have during the day, and the occasional trip around the lake its become obvious that its really a great old car, I wish there were some others around here but so far Iv'e not seen or heard of any.

Edited October 9, 2015 by LAS VEGAS DAVE (see edit history)

[Daves1940Buick56S]

Waitaminnit Dave...you did the OD work by yourself in your driveway? And you drive a motorcycle? And your girlfriend is coming out in Dec? And you're 73? My hat is off to you Sir! (bows deeply)

 

Cheers, Dave

[C Carl]

Yeah , I'll tell you what , brother. YOU might just see the speedo roll over on that Bu' ! Drive it , and with the low miles presently , use all synthetic lubricants , and drive conservatively , could happen ! Best of luck in all your projects , etc. - Carl

[LAS VEGAS DAVE]

Thanks you guys, I am a lucky guy. My girlfriend and future wife is 49 years old (looks 36) and is the best thing that ever happened to me. She was a reporter in the Philippines. I am attaching a picture of her on our bike that we keep in the Philippines, the next picture is of one of my bikes here in Vegas that I ride. I think I am the oldest guy that is riding a V8 Chopper, it has 400 HP and I've ridden it 152mph. People say I'm crazy and they are probably right but if I want an adrenaline rush the bike is there and when I want some peace and just an easy good time at an even less than normal pace the Buick is there. I am really enjoying the Buick. The 33 Ford is one I bought in 1975 as a bone stocker. Since it was a 4 door it wasn't worth to much back then. Over the years I hot rodded it up with a hot rod flathead engine and juice brakes etc. A friend chopped the top in 1982 and I drove it until 2008 when I sold it to a fellow in Germany for a price I couldn't refuse. 

Edited October 10, 2015 by LAS VEGAS DAVE (see edit history)

[jeff]

Yeah, my hat is off to you as well.  Keep doing whatever you are doing!

 

On the temperature at lights issue, I really wonder if this is typical of pre-war Buicks - maybe others can join in with their experiences.  I really appreciate Ben's comments on the basic capabilities of this engine, yet certainly some changes were made from pre-war to post-war 248's.  (fan and pulley sizes, what about the radiator core size?)  If these things were changed, was it because the pre-war stuff was a bit deficient when sitting at a light, or when stuck in traffic? 

 

For me, figuring out these little details is the most interesting part of the old cars.  It's always trying to answer the question - how was it back in the day?  How close can I get to that target?  For example, I love listening to my radio warm up, and begin receiving stations (last winter's project).  Sure, a number of people can drop in a modern setup, and sure, my reception basically stinks using the running boards as antenna, but for me, that's not what I am after.  (Although, I admit, I might someday change the gearing - I'd like to get a 3.9 from a Century.)

 

So, how good should the pre-war 248 be in terms of stop light heating-up?  Did my rod-out of the radiator get me to my goal, or is there still something else?

[Guest gmorse]

With regard to cruising speed, my '39  (248) has 3:90 gears, and 2500 rpm is just 55 mph. It is happy there, and a little less happy at 3000 which is 65 mph. Happy being defined as smooth and relaxed, not straining at all.

Regarding engine temp., here in FL it is usually hot, so overheating can be a problem. I do OK with the temp. around 180, until a stop light. Makes you want to plan your route! Poor water circulation must have been a problem, because in 1941 and newer 248 engines, there was a change to the front of the engine block so they could use the larger water pump, as on the 320 engine. We are just now getting a little cooler weather, not over  the low 80's, so the '39 is happy again. By the way, I have driven this car about 38,000 miles in the last 16 years.

Good luck to all.

Gary

Edited October 12, 2015 by gmorse (see edit history)

[jenz38]

My highest respect dave ...,

Do you still know wheretoo im germany the'33 goes ?

Edited October 12, 2015 by jenz38 (see edit history)

[LAS VEGAS DAVE]

 This morning here in Las Vegas it was only 70 degrees outside while I went for a drive in the old Buick. It seemed like a new car, this was the coolest weather that it's been driven in since I got it. Even at the lights it never quite got to 180, just mostly 160 driving and up 175 at the longest lights. I think if these cars were used in the cooler climates and with the traffic back in 1938 being sparse they probably did a fine job of running cool. Even if they were driven in warmer climates there was probably no traffic so they probably ran under 180, especially at 30 to 45 mlles per hour. This morning was a real pleasure to drive, the car also seemed to be more powerful in the cooler weather. After warming up the car I left at about 3am and drove around relatively empty streets until about 5 am when the first signs of drivers going to work started to appear. With the front windows down and the cool air filling the car along with it being still dark except for my headlights and the streetlights and the silence of empty streets allowing me to hear the tires rolling along the road it was great. I love how quiet the car is, I can barely hear the engine run when sitting at a light and I love the sound of first and second gear as it accelerates from a dead stop. I stopped at the cafe at the oldest original truck stop here in Vegas at a few minutes after 5 am to have breakfast and read the morning paper, as people showed up some wanted to strike up a conversation about the old car and the old days. The truck stop is on the old part of Las Vegas blvd which was the only road from Los Angeles to Salt Lake City back in the fifties.

 Jenz, I don't know where in Germany the 33 went but the guy that bought it was a collector.

Edited October 13, 2015 by LAS VEGAS DAVE (see edit history)

[Janousek]

For your warmer temps in vegas you could up your hot weather ability with a catch can and a pusher elec fan running from a toggle switch.  Building a nice fan shroud will help also.

 

All of these older cars didn't have cooling capacity or designs of new cars.  Mimicking what they are doing today will help you.  I set up a working 41' Cadillac limo with these updates to allow the A/C to keep the car cool during idle time.  Still warmed up but would maintain 190-200 during idle.  Like most cars of this era as soon as the car is driven then the temps drop.  If done right the modifications can be easilly removed and no damage to the originality when converted back.  

 

We used to take my Wife's grandfathers 40' special down the highway running 70mph on severeal trips.  60-65 mph is probably better on the car but it didn't feel like the RPM's were abusing it.  Our straight 8 Auburn running 65 is more than that engine likes.  2600 rpm's on the tach and it gives off a bad vibe.  

 

Our 31' Buick 90 series with high speed gears doesn't brake a sweat at 60 mph.  It will do it from one tank fill up to the next all day.  Even 65 mph isn't bad but start running it at 70 then temps start rising.  Still smooth but the temps go up so I don't run it there.  

 

I believe getting rid of babbit bearings allow the increase of safe RPM's.  Balance the engine with inserts and the rods aren't likely to pound out the bearing.  

[LAS VEGAS DAVE]

For your warmer temps in vegas you could up your hot weather ability with a catch can and a pusher elec fan running from a toggle switch.  Building a nice fan shroud will help also.

 

All of these older cars didn't have cooling capacity or designs of new cars.  Mimicking what they are doing today will help you.  I set up a working 41' Cadillac limo with these updates to allow the A/C to keep the car cool during idle time.  Still warmed up but would maintain 190-200 during idle.  Like most cars of this era as soon as the car is driven then the temps drop.  If done right the modifications can be easilly removed and no damage to the originality when converted back.  

 

We used to take my Wife's grandfathers 40' special down the highway running 70mph on severeal trips.  60-65 mph is probably better on the car but it didn't feel like the RPM's were abusing it.  Our straight 8 Auburn running 65 is more than that engine likes.  2600 rpm's on the tach and it gives off a bad vibe.  

 

Our 31' Buick 90 series with high speed gears doesn't brake a sweat at 60 mph.  It will do it from one tank fill up to the next all day.  Even 65 mph isn't bad but start running it at 70 then temps start rising.  Still smooth but the temps go up so I don't run it there.  

 

I believe getting rid of babbit bearings allow the increase of safe RPM's.  Balance the engine with inserts and the rods aren't likely to pound out the bearing.  

I agree that a shroud would be a definite improvement when the car is idling. An electric fan if it was a puller instead of a pusher could also do a better job than the stock fan. I agree that an upgrade to insert bearings is indeed an upgrade. I've built many hot rods including some using the  flathead Ford which was notorious for running hot. When building a hot rod the goal was different than restoring or maintaining an original car. On the hot rod pretty much anything that would improve the performance or the driving characteristics of the car was just fine. Cooler running, better brakes, steering, tires etc were all goals with originality taking a back seat. I loved building and driving the finished car and it was a reflection or lack thereof of my tastes and mechanical ability. On this old Buick that is my present obsession I'm trying to keep the car as visually  and mechanically original as possible. If the car actually had a problem with boiling over even after the original cooling system was working as it did when it left the factory then I would add a shroud. As it is there is really no problem that adding a little coolant to the radiator if the temp gets hot enough for a little coolant to expel itself out the overflow tube can't remedy. Sure I would like it if the car would run 75 mph on the freeway for a couple of hundred miles at a time but then it would be like a modern car. I'm just as happy and maybe even happier just going along at around 60 and stopping more often in this old Buick. The challenge for me is to maintain the car to a degree where I think I've done as good a job as if I had taken it to a dealership back in the day on a regular basis. I compromised a little already by adding the overdrive. I realize that overdrive was available back then but it was not an option on the Buick and if one was added it would have to be done by a dealer or someone specializing in that conversion. I'm not sure if there was ever anyone that actually had it done back in 38. The compromise was worth it because in reality it was the only way I felt could drive the car at least fast enough not to be in fear of being rear ended if I stayed in the right hand lane of the freeway while at the same time feeling the motor wasn't being stressed.. Driving the old Buick requires more patience and paying more attention to all the gages than getting into my late model pick up and driving it. Thats what makes it fun. I take it for granted that when I get in the pick up it won't overheat and I'll get to wherever I'm going trouble free and when I get back it won't need anything other than more gas. Each trip in the old Buick is a mini adventure, I like that. 

Edited October 13, 2015 by LAS VEGAS DAVE (see edit history)

[C Carl]

Yup ! 'Vegas , you are a car guy , plus ! I love my cars as they are , from my slow , challenging mid ''20s Cads , to that ridiculous money sucking 'V12 'Benz roadster. Yeah , just like love." Love me as I am", they plead. By the way , pre-war traffic jams were not unknown! Go talk to any of your sharp 100 year old friends. Ask 'em. Though there were far fewer cars and folks , the carrying capacity of the roads was also significantly less. I have heard this from old guys who lived in places like L.A. , and others , and I remember my dad complaining about the congestion caused by the "Sunday drivers" as we tried to get from point A to point B in his '39 Pont' in the '40s. This was in Chicago and environs. Oh yeah , did you say "crazy" ? Some people think you are crazy ? Man anybody must be crazy to think that. I still have a few of my old BTTW aspects left , and if I were healthy enough , I'd have more ! But it was a late in life mountain snowmobiling accident that started my accelerated decline. Lots of complications followed , including diabetes from the body damage , and a couple heart attacks. Be careful , my brother , you have a lot to live for ! - Carl

[Janousek]

I used the pusher fan as that let me keep the original fan in place.  The electric fan is hidden behind the condenser or grille in the case of a buick.  Your right, nothing worse to me than opening a hood and seeing an electric fan or an alternator on these old cars.  

 

I'm really surprised your "cruising speed" is around 60 with an overdrive.  I might be trying to compare it to the 40's specials?  Grandfather's car wouldn't skip a beat at 60 and I have a 48' special fastback that I only drove once before It was torn apart but 60 was nothing.  These are Buicks, not Ford or Chevy's of the period that truely wen't anywhere near the same car.  From my experience the inexpensive cars were slow and as the price went up so did the speed and power.   

 

Your chart is helpful to just get an idea of rpms.  I haven't gotten around to it but I was always going to run our 31' with a dwell/ohm/tach just to see what kind of rpm's it's turning.  

[LAS VEGAS DAVE]

Before the overdrive was installed I once drove the car at 70 mph for a short distance to see how it felt, that's about 3700 rpms which is to high in my opinion for continuous driving. Even at only 60 mph which is the slowest speed I'm comfortable with if I'm on the freeway the engine was still turning more than 3000 rpms with the stock gearing. I think any continuous driving should be limited to 2500 rpm or less with these long stroke engines.   Although the cars can go that fast with the stock gearing it would be much better not to drive them at any rpm over 2200 if they are going steadily mile after mile. I don't know what the gear ratio was in a 40 or 48 Buick but the 38 Special was 4.44 which is a very low gear ratio. The Century had a 3.90 I believe which is a little higher along with a little more horsepower to overcome the higher ratio . A 3.90 wasn't used by Buick in the Specials because the Specials didn't have enough horsepower and torque to move the car from a stop or up a hill with the higher ratio and still maintain the performance the factory wanted out of each model. The other models had the larger 320 cubic inch motors and they received the higher gear ratio rear axles to take advantage of the increase in torque and horsepower. There weren't any freeways in the thirties and the highest speeds cars traveled on even when on the best roads were normally under 50 mph. By the way a pusher fan is the least efficient way of moving air through a radiator and it actually starts to block air from going thru the radiator once the car is over about 25 mph. A puller fan lets as much air as the speed of the car dictates go thru the radiator before it is restricted by anything. A shroud is the best way to get the maximum amount of air to pull through the radiator if properly designed and fitted. If we drive our old cars in 100 degree temperatures we should expect that the cooling systems are being taxed to the max, any hill, traffic, tailwind, etc could be the straw that breaks the camels back so to speak. I remember my dad buying those canvas water bags that you hung in the grille hoping it would keep the car from boiling over. All the old V8 Fords were prone to overheating even on the cooler days. Cooling systems today have come a long way. Its almost impossible to make a modern car overheat, they can idle all day or pull a trailer up a long grade and the temperature rarely changes. In the days our old cars were made the drivers had to take into consideration many factors and adjust his driving accordingly if he wanted to be sure of his car not overheating. 

[jeff]

Great comments - I have enjoyed this thread.  I agree with your statements on rpm.  It seems like there are two opinions, both valid.  One opinion is a "back in the day..." opinion, saying that Specials were pushed to 65+ (when the roads allowed!) - so they are able to do this today.  This is true.  But, the other opinion is that keeping the long stroke engine to a comfortable rpm range is wise in the long run, and especially wise now that these cars are scarcer than they once were.

 

My other comment is that the Specials were available with the 3.90 rear, when ordered with the Police Package!  (this is referenced in the '38 shop manual)  This included a higher compression head, and a corrected speedometer gear.  I take this as my "permission" to drop in a 3.90 when I someday find one.

 

Another thought is that one reason for the 4.44 is to give the car nearly shiftless performance.  Try rounding a turn a about 8 mph and just leave it in high.  No problem.  This was as much the mark of a quality car (maybe more) than was top speed.  No excessive shifting required, as may have been true on the customer's trade-in.

 

Of course, the Century offered the best of both worlds.  And, in a few short years, the road speeds would begin to climb - making the Special's design approach a bit obsolete.

[LAS VEGAS DAVE]

Jeff, I had not heard of the Police Package but find it interesting. If the motor had a higher compression head of course its horsepower would be higher which would help with the higher gear ratio 3.90 rear axle. Even with a 3.90 gear rear axle ratio the engine would be spinning 2300 rpm at only 50 mph and over 2700 rpm at 60 mph which is faster than I would like at a steady speed. The police only needed the higher speeds for short distances and they generally weren't concerned with how long an engine or anything else lasted. The Century and Roadmaster even with their bigger engines and 3.90 rear axles still had to spin to fast in my opinion at a steady 60 mph.  An overdrive is the best solution for the Special in todays world but was never offered by Buick on any of their models, Chevrolet was the only GM car to offer the overdrive as far as I know. Ford, Mercury, Lincoln, Chrysler, Plymouth, DeSoto, Dodge, Nash, Hudson, Packard, Studebaker, Rambler and others all offered the Borg Warner overdrives but no GM cars other than Chevrolet. The possible answer might be that GM was working on the automatic transmission and felt that was the future of transmissions. They even had the self shifter transmission in 38 but it was a one year option only and was never offered again. The DYNAFLOW was the next automatic Buick offered and that was about ten years later. I had a few old Buicks with DYNAFLOW transmissions as a kid and they were bulletproof. I used to love those old heavy Buicks with the straight eight and the DYNAFLOW transmissions, they just seemed to float along. I've added a new chart showing all three gear ratio combinations for anyone interested. Keep in mind the advantage of an overdrive over a higher rear axle ratio ring and pinion set is that it keeps the same 4.44 gear ratio if the overdrive is not engaged, this is good on hills or when pulling away from a light.

 

   4.44 (STOCK)                                3.90 (CENTURY AND ROADMASTER)                          OVERDRIVE  (3.10)

   

 

 SPEED        RPM                                           SPEED       RPM                                                  SPEED        RPM

                  

40 MPH       2094                                          40 MPH       1839                                                 40 MPH       1462

 

45 MPH       2356                                          45 MPH       2069                                                 45 MPH       1645

 

50 MPH       2617                                          50 MPH       2299                                                 50 MPH       1827

 

55 MPH       2879                                          55 MPH       2529                                                 55 MPH       2010

 

60 MPH       3141                                          60 MPH       2759                                                 60 MPH       2193

 

65 MPH       3402                                          65 MPH       2989                                                 65 MPH       2376

 

70 MPH       3664                                          70 MPH       3219                                                 70 MPH       2558

 

75 MPH       3926                                          75 MPH       3448                                                 75 MPH       2741

Edited October 13, 2015 by LAS VEGAS DAVE (see edit history)

[Janousek]

I was thinking the 3.90 ratio isn't exactly low.  Your chart confirms this to me.    The 3.42 ratio that gm puts in most trucks looks like a good compromise.   I get the roads weren't all "high speed"  back then but the torque of the straight 8 isn't exactly utilized unless they figured like Jeff said about being able to shift as little as possible.  

 

If and when I get my 48' done I'll commision a set of 3.42 gears if I can't run 70 without beating it to death.  

 

I have a 59' gmc  that had 5.14 gears in it.  It would cruise at 30mph and race at 45mph.  Neat truck but the drivetrain went away in a hurry on that thing.  I drive the old stuff but I'm not going to be a bother for modern traffic if I can help it.  

[LAS VEGAS DAVE]

If a guy put an overdrive in a car that already had the 3.90 ratio rear axle gears he could cruise at 65 mph and the engine would be humming along at only 2090 rpm.To me that would be great cross country gearing.

[Janousek]

No doubt 3.90 with the overdrive would work great.    It's just most guys will do one or the other and not both.  

 

A friend of mine has a very original 37' century 4 door that he recently asked me about putting taller gears into it.  He said it races on the highway but he's several hours from me so I can't drive it and see what is happening.  From what I've been reading the 3.90 was the lowest one ever made.  I was going to dig through the 37-38 stuff and see what they are doing.  I'm surprised nobody has made runs of lower ratios for these cars.  At least I haven't found any.   I can have them made but this owner wouldn't wouldn't be interested in the cost to do it.    According to your chart at 70mph he would turning 3219 rpm's which might be excessive.  

 

Anyone ever put a temporary tach on their cars and see where they feel good?  I'm running out of weather in Michigan but I'll try on our 31' which is very close to a 320 engine.  

[Janousek]

On break this morning I checked with my book  "1948 Specifications"

 

40series   4.45     50series 4.45   70series 4.1

 

 

Optional

 

40series 4.1      50series 4.1    70 series 3.64

 

That 3.64 ratio wouldn't be a bad one if you could find one.  

[suchan]

On break this morning I checked with my book  "1948 Specifications"

 

40series   4.45     50series 4.45   70series 4.1

 

 

Optional

 

40series 4.1      50series 4.1    70 series 3.64

 

That 3.64 ratio wouldn't be a bad one if you could find one.  

The '38 Specials with the semi-automatic transmissions had 3.6 gears. Scarce as hen's teeth, though. I'm surprised no one's repro'd them.

[LAS VEGAS DAVE]

The fact of the matter is that either of the ratios (3.90) OR (3.64) that are rare as hens teeth to find are still not very helpful as far as a cruising speed goes and both of them make first gear closer to what it would be like starting out in second gear with a stock 4.44 rear axle. At only 60 mph the 3.90 would still require the engine to spin at 2759 rpms which is to high and with the 3.64 ratio the engine would be spinning at 2575 rpms which is also to high. This is at only 60 mph which is the minimum speed a car should be at if on a freeway, it would be better to be at 65 but the engines would be spinning even faster.  A good speed for these engines is 2000 to 2200 rpms,  those rpms were what the engines were designed to last at. Those are about the same rpms as the engine is spinning with the stock gears at 39 to 43 mph which feels great when driving a stock car. Sure the cars can be driven much faster but not steadily mile after mile. Even if the car has an overdrive 60 to 65 mph is all the car will do at a comfortable 2000 to 2200 rpms. The easy answer to everything is to stay off the freeways. The other answer is costly, approximately 2300 dollars to add an overdrive.  

[Ben Bruce aka First Born]

 I can not agree that these cars were meant to run at only 40 mph. I PROMISE you, our '38/ two '39s and '40 DID NOT putter along at these speeds. We would have been holding up traffic.! I am talking about driving these in the 1950s. My brother and I were teenagers. We did not drive 40 mph unless forced to. And we never had to replace an engine.  

 

  Ben

[LAS VEGAS DAVE]

Ben when I was a kid I also drove them faster but if you consider that in 1953 65 mph was fast it really isn't that way today. Also we didn't drive them on long trips, at least I didn't. The fact is that at 65 mph a stock Buick Special engine is turning over 3400 rpms. I drove mine before I put in the overdrive at that speed and although it did it with out problems I didn't like it. It would not have liked driving to Los Angeles from here or any long trip at that speed. I stand by my opinion that 2200 rpm should be what to shoot for on a steady one, two, or three hour drive. If its kept at that and the oil changed every couple of thousand miles the engine should last longer than me. 

 Ben, I would like to know what rpms do you think these engines should be at on a steady drive of an hour or two? 

Edited October 14, 2015 by LAS VEGAS DAVE (see edit history)

[Joseph P. Indusi]

Jeff is correct that with the 4.44 rear end the 1948 Special that I had would be easy to drive locally around town without shifting. It only seemed comfortable around 45 MPH on the highway, however. I have long maintained, but have never been able to obtain confirmation, that Buick in the 1940's intentionally put in these low ratios, like 4.44, because they had no automatic transmission so to avoid shifting they used these ratios. I eventually changed my rear out with a 3.4 that gave the car some legs to move along on most of our roads today.

Joe