Gear ratio

[Racur96]

Hey everyone, I’ve been thinking of upgrading my rear gear ratio to be a little more highway friendly. Stock engine . Just curious if anyone had done this and what ratio you chose?

[J Franklin]

Lots of people have done it but you need a ratio that conforms to the weight of your car and the hilliness of the terrain you most drive in.

[30 Closed Cab PU]

I had my truck changed from 4.11 to 3.54. Am satisfied, but I drive lower speeds 45 mph is usually max. Motor is rebuilt, Standard head, but not balanced or built for touring. It will do 55-60, but is in the 2200 - 2400 rpm range maxed out, which personally I do not think is good for a standard motor, especially for more than a few minutes.


Most people who want to run higher speeds 55-60 use a high compression head, touring built motor, brakes and suspension/front end in tip top shape, radial tires, and a Mitchell overdrive with I believe 3.78 rear end (not 100% sure of 3.78). Quite a few also add an oil filter.


If you get the wrong component mix you may have OK speed/RPM, but be lacking in ability to take on hills without shifting way down (lack of torque). This is additional info on J Franklin's Post.


If going to a 3.24 rear end without a Mitchell, consider a high compression head, which also means the motor should be fairly fresh with good compression and Babbitt or Insert bearings to handle the extra load of higher compression and lower RPMs/loads.

[Jim Brierley]

3.54:1 will help, 3.27:1 may be too much for a stock engine?

[wmws]

All good advice above. Just to give you some figures.
A standard 3.78 rear at 2000 RPM = 46 MPH
A 3.78 rear with a 26% Mitchell OD at 2000 RPM = 58 MPH
A 3.54 with no OD at 2000 RPM = 49 MPH
A 3.24 with no OD at 2000 RPM = 53 MPH
I have the Mitchell and am happy with it. A little spendy but relatively easy to install.

[Mike Peters]

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I installed a Mitchel 26% overdrive last summer in our Tudor and am very happy. Best of both worlds. Overdrive for country driving and standard drive around town. 3.78 rear end ratio. Stock engine with stock head handles it very well. When installing the Mitchel, I replaced an old Borg Warner 33% overdrive in the same car, same engine. Honestly, the Borg pulled too hard for that engine. Any hill or headwind was too much, and always had to shift back to standard.

[30 Closed Cab PU]

Originally Posted by wmws

All good advice above. Just to give you some figures.
A standard 3.78 rear at 2000 RPM = 46 MPH
A 3.78 rear with a 26% Mitchell OD at 2000 RPM = 58 MPH
A 3.54 with no OD at 2000 RPM = 49 MPH
A 3.24 with no OD at 2000 RPM = 53 MPH
I have the Mitchell and am happy with it. A little spendy but relatively easy to install.

wmws - That's great info. Thanks for posting it. Perhaps I missed this info before, but do not remember seeing this comparison when researching 2 years ago when figuring out what to do. With the 4.11 I could not comfortably keep up with my club at 40 mph.

[30 Closed Cab PU]

Originally Posted by Jim Brierley

3.54:1 will help, 3.27:1 may be too much for a stock engine?

I believe it depends on your model car (Fordor vs. Pickup/coupe), what shape the motor is in, and what grades you are going to pull. For occasional hills it I've heard it will be OK with Stock, but in foot hills, mountains, steeper grades, and longer grades you may be needing a high compression head, especially if you do not have a Mitchell.


Hopefully others can chime in who live in hilly/mountainous areas that have 1st hand experience.

[Purdy Swoft]

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 .

[GPierce]

Originally Posted by wmws

I have the Mitchell and am happy with it. A little spendy but relatively easy to install.

What rear end do you have?

[Joe K]

I converted my 29 CC pickup to 3.54. Driving it from my parents house in mid-Massachusetts to my new house in Seacoast NH I was followed on the way by my father with "tools, spare parts" and his somewhat familiarity with the car - and a tow cable.

The engine was newly replaced and still on the initial trials - hence the insecurity on my part. (what if we did something wrong?)

We followed the back-roads rather than the more time effective and then quite new Route 495. Route 110 figured heavily in my navigation which is a road which passes through the center of EVERY small town on the way - my rationale being I'd rather coast into a local garage for service by someone who MAY know cars, or leave myself to a "towing service" of unknown destination and probably not trivial cost.

On our trip, I attempted to maintain the speed limits, whatever it was. There are sections of Route 110 which are posted (then) 55mph, and a lesser 40mph as one approaches towns dropping to even 25 within the town limits.

Meanwhile, my speedometer was at best "approximate" and somewhat "in and out." Some issue then and suddenly with the cable ends and pot metal gears?

On our arrival in NH with no problems and having made good time my father had commentary for me. "You drive too fast - you were up to 68 mph at times in a car which you shouldn't be driving half that fast because of your brakes."

I really had no sense of going that fast. The car took it well albeit the soft top on that CC pickup can really get to "fluttering." above 60.

Since then I have resolved both of the speedo issues (broken cable and the cable would "catch" and do a couple of dozen turns and then "disengage", plus the gear ratio correction.)

Joe K

[30 Closed Cab PU]

Joe - Was that with Stock compression Head and stock components? With or without a Mitchell?. I just do not understand, my late 30 comes no where close to that.

[31Tudor]

With a stock engine in a 28 pickup, with a 3:54 rear end, I can run 50-55 all day. Going up into the NC mountains, with that set up, on club touring events, I see no difference in shifts points compared to anyone else. I do think a 3:54 on a 4 door in a hilly area, you may see a difference.

[wmws]

Originally Posted by wmws View Post
I have the Mitchell and am happy with it. A little spendy but relatively easy to install.

I have the 3.78 rear. The nice thing about the Mitchell is if on a hill you can go from 3rd OD to 3rd standard to 2nd OD and even to 2nd standard although I have not found a hill yet that I can't make in 2nd OD.

[31Abone]

Have 32 "B" PU ..had 4:11 had Tom Endy put 3:54 works good about 55 mph..no cigar but about right for 4 cyl...but a 21 stud v8 32 needs 3:27 for sure for 55 -60 mph range...these old rigs don't feel good above 60..not safe

[Joe K]

Originally Posted by 30 Closed Cab PU

Joe - Was that with Stock compression Head and stock components? With or without a Mitchell?. I just do not understand, my late 30 comes no where close to that.

Stock everything except for the Tillotson X.

I have no positive verification of the speed so part of this may be my Dad's parental exaggeration.

But I drove the same 3.54 rear end with a VERY worn out painted red Allstate engine at 55 on the Mid-Cape Highway at Rush Hour - and have told my tale about losing a connecting rod nut - and tenderly driving it home a couple of miles off the Mid-Cape.

With the 3.54 most any engine/car should do 55mph - easily and no sense of imminent dissolution.

Joe K

[Kurt in NJ]

At work many of the customers know about my A, they would tell stories of the A they had in college, driving several hundred miles home and to girl friends places, they all said they drove over 55, but that there were stops for oil, that they got the used oil most times, they never worried about driving "too fast", but that it always got them there, and would have been faster if they didn't have to stop for oil so often
I have stock rear ratio, don't worry about driving over 55, have driven all day at 65+

[J Franklin]

Originally Posted by Kurt in NJ

At work many of the customers know about my A,----
I have stock rear ratio, don't worry about driving over 55, have driven all day at 65+

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.

[Tom Endy]

Originally Posted by wmws

Originally Posted by wmws View Post
I have the Mitchell and am happy with it. A little spendy but relatively easy to install.

I have the 3.78 rear. The nice thing about the Mitchell is if on a hill you can go from 3rd OD to 3rd standard to 2nd OD and even to 2nd standard although I have not found a hill yet that I can't make in 2nd OD.

My recommendation is to install a Mitchell 26% overdrive. This will give you many advantages. High gear overdrive for going above 45 mph comfortably and second gear overdrive for going up and down steep grades. The cost is about $2500, about twice the cost of changing out the ring & pinion. However, it is a good investment as it adds to the value of the car and it can be removed without leaving alteration to the car and they are easily sold.

Tom Endy

[Synchro909]

Originally Posted by wmws

Originally Posted by wmws View Post
I have the Mitchell and am happy with it. A little spendy but relatively easy to install.

I have the 3.78 rear. The nice thing about the Mitchell is if on a hill you can go from 3rd OD to 3rd standard to 2nd OD and even to 2nd standard although I have not found a hill yet that I can't make in 2nd OD.

The motor in my Phaeton is very good but even then, there are hills I have to climb out of my place even before I get to the main road that require a bit of skill to get up even in standard 1st gear when I'm towing my camper. It weighs about a tonne and I have to zig zag my way up the hill to get there. Once out in the open, I am very happy with the 3.78 rear end and 26% Mitvhell O/D. We travel at 50 mph all day, every day (our longest single trip so far has been 14,000 miles)
At the other end of the scale, I have a 1928 Tudor with a B motor. The motor is fitted with a 5.5 head and Stromberg downdraught carburettor. The rear end is 3.54 and there is another 26% Mitchell in front of that. I find that to be too much. Fuel economy is terrible, it almost stops if a hill even comes into view, it is hard work driving it and it hates a head wind. The tyres were getting low so I recently put a set of 19" wheels on it hoping that the slightly smaller diameter would help. It did not. I see a 3.78 set of gears going into the rear end of that car pretty soon - once I save up o buy them.

[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]

Originally Posted by J Franklin

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.]

Originally Posted by Purdy Swoft

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]

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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]

Originally Posted by 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 .

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.