Gear ratio

[Kurt in NJ]

I think Ford did a good job with stock rear ratio, if you start doing modifications it has to match--- put in a cam that raises the torque peak and then change the rear to make the engine run below torque and you can end up with poor fuel economy and low power, functionality lugging the engine
Years ago the rear went bad in parents motor home, I had a cube van and the rear was borrowed from it, the original rear in the motor home was 4:11, the cube van has 4:56, with that rear the motor home got 1 more mpg on a trip to Florida--- 10% more mpg--and yes, the cube can sometimes sound like it needs another gear

 

[Kurt in NJ]

I don't think your story is too useful to most new model A owners.They should drive more conservatively and keep the engines going longer.

So I have been trying to break my engine, it's been over 30 years--- speeds over 60 all day, 3rd gear starts, long parade in first at very slow idle, constantly using full throttle, -- the next day after new Babbitt I knew it would go 67, it's the first engine I poured my own, how will I know how good I did if I don't try to break it--- the engine I paid to have done before was carefully broken in, after 500 miles it wasn't driven over 50, it only lasted 3000 miles till Babbitt failure---- if you have to drive it easy to "save the Babbitt" it wasn't done correctly

 

[wmws]

So Kurt, How many RPM is your engine turning at 65 MPH with standard 3.78 rear?

 

[Patrick L.]

I prefer the 3.78 gear ratio . Henry thought that the 3.78 ratio was best for the model A . Low and mid range power is more important than actual top speed for me . For the most part , fifty MPH is fast enough for the model A .


My original mechanical brakes are as good as most hydraulic brakes . I feel that a person would be lucky if they survived a wreck at 55-60 MPH in a model A .

Yup !

 

[TerryH]

Kurt has the only A I know of that can do that. Good for him, but not reality for the rest of us, as we have found out.....

 

[Racur96]

I’m running a stock style engine , not a touring or highly modified. My engine runs great and has no issues . Not trying to get crazy just wanting a little more mph. We have the occasional hill but nothing constant or mountainous. 3:54 may be a good option from what it seems .

 

[The Master Cylinder]

I’m running a stock style engine , not a touring or highly modified. My engine runs great and has no issues . Not trying to get crazy just wanting a little more mph. We have the occasional hill but nothing constant or mountainous. 3:54 may be a good option from what it seems .

Maybe I missed it but I don't see where you ever mentioned what you have. PU, coupe, Town Sedan?? The weight can be a deciding factor.

 

[30 Closed Cab PU]

I believe I read somewhere that converting from 3.78 to 3.54 is a gain of 4-5 mph at 2000 or so rpm.

 

[daveymc29]

I have a roadster with 3:27 rear, 400 x 16 tires and a 26% mitchel. Handles the sierras easily with a few 3nd o/d shirts on the long steep parts. I have a good "touring" engine with police head (5.5)
on my coupe i have an unknown engine with 94 psi in all four holes, 3:78 rear with 36% b/w o/d. I haven't gone over the sierras with it yet, but it seems to handle the coast range rather well with only occassional 2nd over stretches on long pulls. I drive both in the 55 mph range + or - a tad. All 400 x 16 tires, no radials.

 

[mike657894]

Gps your speed. you have a tach? If your not getting 55mph or more out of a stock engine you have tuning work to do. or repair. My car drives nice at 50 but is moving around the lane a lot at 55. I need to work on steering and maybe king pins now. Before I go faster. Stock gear stock engine b cam. top speed so far 57 1930 briggs fordor. carb poor ignition poor

 

[Racur96]

29 closed cab pickup .

 

[GPierce]

I am running a stock engine in a 31 CCPU with a 3.54 in West Tennessee. Pulls the hills fine and will run 50 to 55 if I want to.

 

[Tom Wesenberg]

I put a 5.5 head and a 3.27 ring and pinion on my friend's 31 wide bed pickup, and it's the perfect driving machine.
The rest of the engine and pickup is all stock.

 

[ryanheacox]

I agree with Kurt, Patrick and Purdy. I know the stock ratio works well for me. Good power mid range, climbs hills nicely, and doesn't feel like it's working to hard even at 50-55. This is with a 5.5 head and a "touring" cam from Brattons, everything else in the drive train is stock.


Just for kicks I tried to see if the new engine could do 65, it could but it wasn't happy about it. Perfectly happy to buzz right up to 55 but faster than that was pushing it hard.


EDIT: Just remembered that the speedo is about 3-4mph slow so I was closer to 68-69. Either way, I would not recommend going that fast.

 

[MALAK]

Here's a gear ratio/MPH calculator I did some time ago. Assumes a 19" tire with a 30" diameter and shows the various RPM vs MPH of 3:78, 3:54, and 3:27 axle ratios with/without a 26% Mitchell OD. The 4-Speed is in there because one of my cars has a 4-speed and I wanted to see the effect of the Axle Ratios and OD on that granny 1st gear.