What Defines Over-Revving The Model A's Engine

Richard in Anaheim CA said:
Henry Ford said every Model A would go 65 MPH, He did not say drive at a continuous 65 MPH. Any Model A done right is good for 45-50 MPH continuous and 55 if the occasion arises.

On my long trips I like to keep it at 1900-2000 RPM continuous all day "in overdrive".
Now that should evoke some comments.

Richard
Anaheim CA
Click to expand...

Richard, with OD at 55 are your rpms at 2k? Do you ever do 60?
 
Holy cow a lot of math here. Just listen to the engine it will tell you. If you are in a hurry you are driving the wrong car.
 
"He did not say drive at a continuous 65 MPH. "


When my Grandfather sold them new the salesman were to take them on the only local paved road and show they would go 65. It was a sales gimmick.
 
Some comments.

First off you all need to do some historical reading and not just guesses and opinions not based on facts.

If you read period magazines and newspaper articles you will find that people talked a lot about driving their full out on all the roads of the day. In some cases that included no roads. My favorite was an oil company in the mid 30's or so doing a reliability run. The used a tudor with some miles on it and the tore the engine down and measured it. Then they put it back together with no new parts. Filled it up with their oil and drove from Phoenix to San Diego (pretty sure I have the towns right) been a while so some details will be off slightly. They drove as fast as they could. They averaged total time like 60 MPH. That is distance from Az to CA over total time including fuel and food stops. Going through mountains and areas where roads did not really exist.

You can also read about people setting records in their A's for going cross country and to Fl from NY. Then there are the people the drove backwards across country.

Then you talk to the people who used the cars everyday and they have story after story about flying down the roads 50 to 60 MPH.

So Yes they really did drive the cars hard when the cars were just everyday cars.

So to answer the question about top end. Really the answer lies in how well balanced is the engine and how good are you at setting spark. The two things that kill the engine are balance and pre-detonation. Most of the engines out there today are out of balance in weight and poor machining. So even getting the engines safely up to 2500 rpm is a chore.

My experience driving a stock well balanced (not as well balanced as I would make it today I should add) A is they really cruise fine up at 55 to 60 MPH and get over 20 MPG.

Quite frankly you can beat the crap out of a properly built A and it will just keep working. The biggest issue is knowing you are not causing pre-detonation. They will do jumps and drive around the stuck 4 wheel drive trucks in the woods.
 
35 years ago I read in a hot rod mag where someone asked "How do I know if I've over reved my engine?'. The answer given was, "localized pains in the left rear pocket and the realization that your engine will now fit loosely in a 5 gallon bucket". Personally, I like the answer given "your engine will tell you". With mine, I don't know what RPM it's running at but I do know that if i go over 45-47 MPH it starts to vibrate and does not sound happy. If I stay at 43 or less it does sound happy.
 
gmNt9k2.jpg


Your crankshaft bearings are protected by the hydrodynamic principle.It is a hard and fast law,.001 clearance per inch of shaft diameter,which is why model a rod and main bearings are ideally clearanced at .0015.

The stock model a crankshaft is dynamically balanced but does not have offset weights to counter balance power stroke impulse.

At maximum rpm,this power stroke impulse results in a flexing of the crankshaft (according the the late Herm Kohnke) as much as .001 flex at the center main bearing,resulting is a loss of the hydrodynamic principle and a failure of the bearing.

If you run an harmonic balancer it helps reduce this potential damage,also a lube line directly from the oil pump with a full flow filter down stream helps pressurize the center main bearing,providing some protection from the loss of the hydrodynamic principle that occurs.
 
In 1927 when Ray Dahlinger drove a new Model A around the USA as a Ford publicity stunt, what speed did he drive at?
 
"the late Herm Kohnke" ???????


pre-detonation ??? no such thing. pre-igntion and detonation which are 2 different animals.


The main problem I see with driving at 65mph is not the driving part, but, the stopping part. [ even with perfect brakes] That said anyone can operate their vehicle any way they wish. Over the years some say they drive/cruise at 65 and others say they run theirs at WOT in all gears until they reach the speed they want. To each their own.
 
Patrick L. said:
"the late Herm Kohnke" ???????


pre-detonation ??? no such thing. pre-igntion and detonation which are 2 different animals.


The main problem I see with driving at 65mph is not the driving part, but, the stopping part. [ even with perfect brakes] That said anyone can operate their vehicle any way they wish. Over the years some say they drive/cruise at 65 and others say they run theirs at WOT in all gears until they reach the speed they want. To each their own.
Click to expand...
While I agree that everyone is free to drive as they wish, I think (at least for me) the point of these "cruising speed" discussions is to determine what is considered best for the health/longevity of the engine and why (the "why" part is important to me). I don't want to drive around at 20MPH thinking that I'm saving my engine if 40 or 50MPH is just fine and I don't want to be driving at 50-60MPH thinking that it's just fine to find out down the road (no pun intended) that my engine pound3d out the bearings prematurely because of it. So, yes, anyone can operate their "A" anyway they choose but it's best if that choice is an informed one. JMO.
 
Second point, even if you have a counter-weighted crank, with only three mains the weights are pretty far off-center from the actual rotational masses they attempt to counter. The offset opposing centripetal forces then bend the crank sections out of line in an RPM relationship that is exponential, not linear.

Third, an A has no front harmonic damper to prevent the severe 'ringing' shock waves that travel back and forth from front to rear along the crank. I wouldn't want to run all day at 3000+ rpm and heavy throttle unless you like swapping out broken cranks.

The above is from MikeK. This is true, and is what causes broken cranks. It is called 'nodulation', the rear flange is constantly forced to 'wobble', and eventually breaks. a friend was in the navy in WWII, and drove his A roadster every weekend from LA to San Diego, always with his foot solidly on the floor, never any problems. I run my speedster to 4100 RPM on hill climbs. It is a B block, C crank with stock oiling except for a full-flow filter. I do have a high volumn oil pump but not sure that makes any difference?
 
Licensed to kill said:
While I agree that everyone is free to drive as they wish, I think (at least for me) the point of these "cruising speed" discussions is to determine what is considered best for the health/longevity of the engine and why (the "why" part is important to me). I don't want to drive around at 20MPH thinking that I'm saving my engine if 40 or 50MPH is just fine and I don't want to be driving at 50-60MPH thinking that it's just fine to find out down the road (no pun intended) that my engine pound3d out the bearings prematurely because of it. So, yes, anyone can operate their "A" anyway they choose but it's best if that choice is an informed one. JMO.
Click to expand...



I understand. Its tough to figure out what to do sometimes isn't it. So how does your 'A' feel ? It'll have a comfortable speed and it'll let you know what that is. I think the majority are comfortable in the 40-50 mph area.

Our family business started in 1918 and I was brought up in it. I grew up hearing that these Fords shouldn't be driven over 50 mph because they would then pound the bearings to death. Many do exhibit the secondary vibration at around that speed, but, I'm not sure I believe they will do that. I've seen quite a bit of bad/ruined babbitt but think it was just due to poor babbitt repours or old age. I've seen only one broken crank and believe it was due to a poor regrind.
 
It looks like few people bought a model A for a model A. I bought my A to slow down, I have enough stress in my life
 
katy said:
In 1927 when Ray Dahlinger drove a new Model A around the USA as a Ford publicity stunt, what speed did he drive at?
Click to expand...

As fast as he could to get back to Evangeline if Henry was lurking about:):)

Kevin I read that article years ago about the endurance run LA to Phoenix you are right about that. The Model A was a '28 or '29 Roadster as I recall, and I believe it was promoting Mobil oil. They drove that Roadster really hard with no ill effects.

I wouldn't do that myself, today. As someone here said earlier 'If you are in that big of a hurry, you are driving the wrong car':eek::eek:
 
Grandpa once told me "If your engine is screaming loader then the guy in the trunk, you are over revving your motor"

I'll always remember my Grandpa’s last words before he died “Pints! Gallons! Litres!”
That spoke volumes to me.
 
I have a 1930 Tudor and it cruises nicely until about 50-52 MPH. As I exceed those speeds the noise and vibration greatly increase. I am not sure if I have the original 3.78 gears or if they have been upgraded to 3.54 gears. I am thinking about getting a tachometer so I can figure out what gearing I have, but I am not sure it matters because anything over 50mph is overrunning the brakes anyway. But, I would really like to know what RPM is considered the maximum RPM a model A engine can run over long periods of time.
 
I'd say on a stock engine redline is around 2500RPM and the never exceed speed is around 3000RPM. Like Bob says in his first post that is roughly 60 and 70MPH respectively. This is only my opinion.



I feel comfortable cruising at 50 (~2200RPM) all day long and the car seems to run nice and smooth at this speed. A little slower and I get an annoying vibration and much higher I'll be well over most posted speed limits around here and there's no need for that in an A.
 
You must log in or register to reply here.
Back
Top