Can you run an A wide open?

29RPU

29RPU

Senior Member
I hear stories about guys racing a circle track in the old days with the pedal to the floor. Another one talked about "runnin 'er wide open, I could get to 54 mph". I suspect this isn't good on an engine, but how safe is it to run the pedal to the floor on model A engines? Can they be over reved that way, or are they not able to reach a critical RPM? Just curious what you guys have done and what the consensis is.
 
Depends

A factory engine was carefully balanced and would go over 60 mph. So an engine brought back to factory specs should have little troubles.

Babbitt is a bearing that let's the crank spin. The enemy of Babbitt are conditions that let the Babbitt be pounded. Out of balance and lugging are the two conditions you need to avoid. Running high rpms with a balance system is a good condition.

Finding a properly balanced engine today is another story. Many A's are not well balanced and will beat themselves up at high rpm.
 
My tired, mostly-original 81,000-mile '28 Special Coupe will do about 58 MPH, flat-out, on level road, dead-calm or with the wind behind it. Speedo might be reading 5 MPH "fast" at that speed.

That's about 2300-2400 RPM, doing the math against the 3.78 rear and 4.50x21 tires.

A lighter body will achieve a slightly faster top-speed ( all other aspects being equal): a Roadster is probably lightest / quickest, a Sedan or Wagon would be the slowest, due to weight. A speedster with completely stock running-gear might achieve 75 mph or better ?

Running "wide-open-throttle" with no load on the engine may push it into self-destructive territory.

Apparently, one of the self-limiting factors of an original A is the "breathing"... the original Zenith carb and updraft intake are considered to be fairly restrictive, and that has a limiting effect on top-speed / max RPM. Probably keeps the stock A at or below the danger zone.

Some guys like to bore-out the intake throat of the stock manifold to gain better breathings and a little more speed.

As far as the babbit bearings go, poured babbit bearings are best for "rotating applications" - main bearings, line-shaft bearings in factories, pillow-blocks for band-saws, etc...

Applications where there is reciprocating or percussive load ( rod-bearings ) tend to have a shorter life. Excessive bearing clearance accelerates damage, by allowing the bearing to be "pounded" each time the reciprocating assembly stops and changes direction.

If you want to learn more about this aspect, find a copy of the "Auto Math Handbook", and study the section where they discuss "piston travel speed" and "reciprocating mass" and its effects on rod and wrist-pin bearings. The reciprocating assembly has to come to a complete stop and reverse direction twice for every revolution of the crankshaft... start winding-up the engine, and those forces can become destructive.

Also, the gravity /splash oiling system of the A may not be sufficient for sustained flat-out running...

I try to keep my speed at 50 MPH or less.

"Back in the old days", Model A's were common and cheap; if the boys blew-one up on the dirt track, they could go get another for $15-$25 and go flog that one...

Not the case anymore...
 
I don't make a habit of it any more but I have run my dead stock 30 coupe flat out for extended periods. Tops out in the low 60's.
 
Henry Ford wrote about the Model A:

"The new Ford will ride comfortably at fifty and sixty miles an hour. It has actually done sixty-five miles an hour in road tests." Henry Ford
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With all other things in good working order as original, all it would take is a supply of NOS original camshafts and the speeds above would easily come back to life.

Larry B.
 
Oiling starts to become iffy after 45 MPH I was told by a respected engine builder who knew a bunch. Used to just go to the dealer for a rebuilt engine installed for a few dollars, so why not run it flat out? Oh yeah those old dirt roads kinda slowed you down
 
As far as the babbit bearings go, poured babbit bearings are best for "rotating applications" - main bearings, line-shaft bearings in factories, pillow-blocks for band-saws, etc...
Click to expand...

If you get a chance, read about Harry A. Miller's 91 CID straight 8s running Babbitted rods and mains at near 8000 RPM for long enough to win Indianapolis multiple times in the mid twenties.

John
 
I have a Model B motor in my 31 coupe. It's a diamond block with 0.60 over bore, Snyder's high compression head, Ansen downdraft intake with a Stromberg 97 carburetor, Mallory distributor, 38lbs lightened flywheel, backed by a 39 transmission. I'm running 700x16 tires on the back and I'm guessing the rear is 3.78, but I'm not sure. On a nice open stretch of highway I can bury the speedometer which is 75mph and that's holding it to the floor.

My goal is 100mph some day. They use to set land speed records with them in the late 30's and 40's and run 130 to 140 mph. Running wide open isn't good for them, but every once in awhile I don't see why it would hurt.
 
Put 4 bends into a coat hanger so it is the same shap as the Model A crandshaft and run it in a drill at 2,000 RPM and see what happens. Wear a leather glove to support the outer end, just as a Model A bearing would support the crank. The Model A crank is just a large bent wire. Without counterweights the Model A crank acts just like that bent wire and the bending forces are squared as speed doubles. I like to keep my speed 45 and below and will probably do the same even after I add counterweights.

My cousin inherited her dad's very nice original 41 Chevy 1 1/2 ton truck, which her dad bought new. She lent it to some fool that thought he should be able to drive it 65 on the freeway. He put a rod out the block and after setting untouched for 10 years, it finally went to the scrap yard.

A fool and his toys are soon parted!
 
J Franklin said:
Oiling starts to become iffy after 45 MPH I was told by a respected engine builder who knew a bunch. Used to just go to the dealer for a rebuilt engine installed for a few dollars, so why not run it flat out? Oh yeah those old dirt roads kinda slowed you down
Click to expand...

It sounds like he needed an excuse for bearing failures. I've done thousands of miles over 60 mph without a hint of bearing problems or even having to take up for wear on the bearings.
 
Tom, really. With all due respect there is no comparison with a coat hanger and a model A crankshaft!!!!!!! We like to cruise on the highway at 50mph, any slower and we may get ran over. If everything is in good condition 50 mph won't hurt.
 
Bruce in southern OH said:
Always a good rule to live by when you drive an A, Don't drive faster than your ANGEL can FLY!!!!!!!!! Bruce
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Hi Bruce, I love it. That would be true for any vehicle, really.
Yes, you can run a "good" model A under load wide open. Thus damped, the engine will not over-rev with its stock cam and carb.
I had my own 29 roadster (b cam, 5.5 head, and Burlington crank) up to 70 mph just for a test, but I got nervous when I realised that I might be outrunning my Angel! LOL
 
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Also remember that your skinny tires are put on BY HAND. I've been to 65 mph and seen my life flash before my eyes when the crosswind hit! Oh yeah, mechanical brakes, that might give you pause.
 
As mentioned in my post above, even Henry Ford implied that one should not run the Model A wide open, i.e., 65 miles an hour as in road tests.

Now do any of you think that Henry Ford himself would have made a statement about comfortable driving at 50 to 60 miles an hour if the Model A was going to throw rods or come apart? ....

Naturally, if your Model A has thicker babbitt and a crankshaft ground down so many times it's about like a toothpick, OR high mileage with shims removed OR unknown condition of bearings from a lot of use, it's best to putt putt 45 in your Model A.

BUT, as it was when Henry made it, the Model A was made to run! Wouldn't Ford have lost his credibility if the Model A engines had come all apart shortly after purchase.... "Sorry, you shouldn't have gone over 45."

The crankshaft whipping and worn out center main didn't happen overnight either. People drove them for miles with no problems.

All this reminds me of a statement a friend made to me 31 years ago when I first got into Model A's. My friend, who was a grown man when the Model A was new and a mechanical engineer, said that if the men alive back then could come back and watch how many of the Model A'ers drive today, they'd laugh!


Larry B.
 
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I've had my coupe for 50 years this year and when I was in high school I used to power-shift it, run it up hills until the exhaust manifold glowed, and rode it down Storm King Mountain near West Point NY at full bore (well over 65!). That was then. After new bearings in 1962, and a complete restoration in 1988, we feed it ice cream these days. I'll go 50 if forced, but 45 is generally my limit. It's not that the car won't do it, it's more a case of preserving the engine. I have no intention of possibly harming a good engine because some guy in a Honda or BMW is in a hurry. BTW, I still have the top half of the transmission case and cluster gear pieces in my barn as reminders that these cars can take much abuse, but not for a steady diet.
 
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