Engine RPMs

Billy 1931 Model A

Billy 1931 Model A

Member
What speed do you find yourself shifting into 3d? Is there a chart of RPM v. MPH for each gear in the Model A? I find myself driving around town in 2d at higher revs, because the engine seems happier than at low revs in 3d. What's your experience?

Love this car.
 

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1-2 at 5-8 mph
2-3 at 12-15 mph
Thats per owners manual

30 mph is just fine in high gear, but, its up to you
 
Here's a table I made mapping RPM to MPH based on the gear ratios. It lines up pretty closely with the mapping in Tom's article. A good rule of thumb is that your RPM for a given speed in 2nd gear is approx. twice the RPM for that speed in 3rd gear. So to upshift, you drop the RPM by half, and to downshift you double it.
 

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So if you're good cruising around at 45-47 mph (2,000 RPM) why wouldn't you be comfortable upshifting from 2nd at 25 mph? Why would you upshift at 12-15 mph? (only 950-1,200 RPM)

Upshifting to 3rd at 12-15 feels way too luggy for me.
 
Mister Moose said:
So if you're good cruising around at 45-47 mph (2,000 RPM) why wouldn't you be comfortable upshifting from 2nd at 25 mph? Why would you upshift at 12-15 mph? (only 950-1,200 RPM)

Upshifting to 3rd at 12-15 feels way too luggy for me.
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I upshift and downshift usually at 20-25. Like I put in the post, those speeds came right from Ford.
 
Patrick L. said:
I upshift and downshift usually at 20-25. Like I put in the post, those speeds came right from Ford.
Click to expand...
One of the things to consider when using Ford’s data is the conditions of the roads in ‘28 - ‘31. Those numbers sound good if you’re driving on a dirt two track.
 
Patrick L. said:
I upshift and downshift usually at 20-25. Like I put in the post, those speeds came right from Ford.
Click to expand...

More info needed. Was Ford expecting level ground? (there's no hills in Detroit) If you think you're going to upshift on a hill at 12-15, you might want to reconsider. Was Ford accelerating rapidly, or content to putz along and keep low manifold pressures so there would be no lugging, and accelerate to 45 in 5 miles?

I suspect those are upshift speeds for gentle acceleration on level ground so mileage is optimized.
 
I shift 1st to 2nd at 10 mph. 2nd to 3rd at 20 mph. 3rd to Mitchell OD (26%) at 40 mph. I think there are those that believe an engine is only good for so many revolutions, so they may try to conserve them. ;)
 
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Getting back to the original question, one of the sales pitches for the original Phillips automatic spark advance was that you could shift into 3rd at lower speeds. It could be that drivers' preference for when to shift into 3rd is partly a function of where they park the spark lever while driving.
 
denis4x4 said:
One of the things to consider when using Ford’s data is the conditions of the roads in ‘28 - ‘31. Those numbers sound good if you’re driving on a dirt two track.
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20 on the low end and 25 on the high for me depending on road conditions. Any slower than 20 would be out of the question for me and most of my shifts into 3rd are around 23.
 
Mister Moose said:
More info needed. Was Ford expecting level ground? (there's no hills in Detroit) If you think you're going to upshift on a hill at 12-15, you might want to reconsider. Was Ford accelerating rapidly, or content to putz along and keep low manifold pressures so there would be no lugging, and accelerate to 45 in 5 miles?

I suspect those are upshift speeds for gentle acceleration on level ground so mileage is optimized.
Click to expand...





Don't ask me, I'm just repeating what the book says.
If you need more clarification then you'll have to wake up Henry and ask him. ;)
 
denis4x4 said:
One of the things to consider when using Ford’s data is the conditions of the roads in ‘28 - ‘31. Those numbers sound good if you’re driving on a dirt two track.
Click to expand...




The roads have certainly changed, but, the cars haven't. Ford wrote the book.
 
Patrick L. said:
Don't ask me, I'm just repeating what the book says.
If you need more clarification then you'll have to wake up Henry and ask him. ;)
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The subtext of this approach is that Henry's word is best, final, and all knowing. I think automotive engineering, road construction, and best driving practices have changed since 1928. In addition, Henry's recommendation without context of why he recommended something is just part of the story, and an old story at that.

I think I'd follow an experienced modern Model A engine rebuilder's advice, or a consensus of rebuilders, more than a 93 year old book.
 
I often feel sad for those who have never driven a Model A Ford. There can be no finer sound than starting out from a stop sign and getting up to 10 mph, going to second and hearing the new sound of second gear at 15 mph with a fairly new, rebuilt transmission. There is no reason to drive any quicker, the Model A is made to do some lugging. That is why it is geared to go around corners without downshifting. The key word is to be "gentle", enjoy the ride and allow the car to provide the longevity that is built into it. Ed
 
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