Touring rear end ratio question 3.78 vs 3.56
 

What do you think would be a better ratio 3.78 or 3.56?

New engine, larger intakes, Snyder 6.0 head, B grind cam, and a F150 trans with 26% overdrive.

I do a mixture of in town and highway driving.

I am about to install everything, so now is the time to make a change if needed to be.

I currently have 3.78 in it now but have access to 3.56's.:confused:

Re: Touring rear end ratio question 3.78 vs 3.56
 

IMHO, I think 3.56 will be too tall with the overdrive.

Re: Touring rear end ratio question 3.78 vs 3.56
 

^^^^

I agree. You have the overdrive, keep the stock rear gear.

Re: Touring rear end ratio question 3.78 vs 3.56
 

Depending on percent of overdrive , Many prefer a 4.11 ratio . I don't use overdrive because horsepower is made at higher rpm . Its way too easy to lug the engine with higher gear ratios . I run the 3.78 ratio in all of mine and feel that it is the best all around ratio . I really don't care that much about running mine much over 50 mph . If I ever drive my model A's over 50 mph it is only for a short distance as in passing or getting ouy of the way of fast moving vehicles . My cars drive and handle very good , Its just that surviving a wreck at 60-70 mph in a model A would be slim to none , for the passengers or the driver .

Re: Touring rear end ratio question 3.78 vs 3.56
 

not to mention the overdrive of the f150 trans before the overdrive...

Re: Touring rear end ratio question 3.78 vs 3.56
 

I use the 4.11 in my two A's. Both do very well around town and on the highway. Too high a ratio can be hard on engine bearings and give fewer MPG.

Re: Touring rear end ratio question 3.78 vs 3.56
 

I would stick with the 3.78.
I also have a new engine with larger intakes, Snyder 5.5 head, Stipe IB330 cam and the F150 tranny with 27% OD. Makes cruising at 50 along with the rest of the guys a dream. Just have to remember to take it out of OD going up hills. It will certainly take the hills in OD, but I just don't want to take the chance of lugging the engine unnecessarily.

Re: Touring rear end ratio question 3.78 vs 3.56
 

I have been buuilding those OD 26% F150 trannys for Model A's for almost 20 years. have one in my 31 coupe. I do not and will not recommend putting the 3.54 rear end coupled with the 26%OD. Too much OD. 3.78 is almost purrfek. My coupe has an almost identical engine in it and is very comfortable cruising at 55 -60 mph. ken

Re: Touring rear end ratio question 3.78 vs 3.56
 

I have a Fordor (heavy car). 3.78 with a 26% OD is a 3.00 final ratio. Works good but perhaps a 4.11/1 ratio would be just as good. Maybe even better with the heavy Fordor.That would be a 3.26 final drive ratio in OD. With a 3.78 and 26% OD, 2200 rpm will give you 63 mph. A 4.11 and 26% OD will give you 58 mph. The 3.78 stock ratio will give you 50 mph at 2200 rpm. I think either the 3.78 or the 4.11 would both be ok, but the 3.54 is definitely too much with the OD.

Re: Touring rear end ratio question 3.78 vs 3.56
 

A lot depends of the weight of your car and if it is a RPU as against a saloon, I would not hesitate to use the higher ratio. My motor is a similar spec to yours and my speedster is only a couple of hundred pounds lighter than a RPU, but it pulls the 41% overdrive effortlessly including on hills but I appear to have a standard diff ratio. I haven't checked it, but it is in a quick change diff (Must work out the ratio one day!)

Re: Touring rear end ratio question 3.78 vs 3.56
 

I have had the Mitchell 26% OD, with the 3.78 rear end in my Town Sedan for over 11 years now, along with the 5.5 head. I think it is a perfect combo. I also agree that 3.56 is getting too tall. On the freeway I like to cruise at 60, which is effortless, and quiet.

Re: Touring rear end ratio question 3.78 vs 3.56
 

I was running a 3.54 in my Victoria and I put a Mitchell overdrive in it. one of my Model A friends said it would to high geared. he was right, it was great on flat ground or down hill but on any kind of incline I would to drop out of overdrive. so I pulled the Mitchell out and going to put in my 160A with a set of 3.78`s

Re: Touring rear end ratio question 3.78 vs 3.56
 

I find it interesting, “The Need For Speed”.

These are antiques. What has happened to the nice drive, on a scenic road, enjoying life and the Model A.

Does anyone driving at these speeds ever think about what would happen at speed in a crash?

Or is this just turning into a “mine is bigger than yours”.

Re: Touring rear end ratio question 3.78 vs 3.56
 

OK, thanks guys. It is pretty much unanimous to stay with 3.78. Less work for me.

I should have also told you that it is a roadster.

WHN, I like to go for scenic drives but I also like to get on the highway and sort of be with the traffic without the engine screaming.

Yes the A is an antique but there is no reason not to help it out with directional lights, LED's, brighter lights, and a better transmission and still keep the look the same.

Re: Touring rear end ratio question 3.78 vs 3.56
 

I have a 26% Mitchell overdrive in my "Touring" Phaeton and find it an awesome combination with a 4:11. The combination is good in the mountains and on a flat highway. I lost a pinion tooth about 3 years ago and when rebuilding the rear end I installed a new 4:11 gear set. I pondered the selection at that time but never seriously considered changing to anything else. This ratio has taken us lots of places!

We are from Minnesota but head for the mountains every chance we get in our Model A.
I also have the same engine you describe so....Getting on a freeway and keeping up with the traffic in the right lane is not an issue. With a 26% overdrive and 4:11 rear end it is easy to maintain 65 mph on a flat road and over 70 if you are brave (crazy) enough. I would not want a higher ratio.

JMO: I build Model A engines so I understand how they should be used to maximize their service life. Even using a 4:11 rear ratio, one has to be careful to avoid lugging the engine. It would be more difficult with a higher ratio rear end. Lugging a Model A engine with high ratio gears will decrease your engine life. Both bearings and cylinder walls will suffer. When driving into a good headwind on the freeway, even with the 4:11 rear end, I often cannot use overdrive as it would be too hard on the engine.

I have over 90,000 miles on my engine and Mitchell 26% overdrive using a 4:11 rear end. Engine and Mitchell have worked flawlessly. Rear end...well I cannot make the same claim... lost that tooth when the pinion nuts came loose after 70,000 miles. Most likely my fault when installing the Mitchell!
Good Day!

Re: Touring rear end ratio question 3.78 vs 3.56
 

Dave, just so that I understand.

If you had a 3.78 wouldn't that be better than a 4.11? You would be able to do 65, but have the advantage of a lower rpm. When coming to a hill just downshift.

Is the fear that you would be doing to much lugging?

Wouldn't a little lugging be better on the engine than a sustained higher RPM?

Signed confused:confused:

Re: Touring rear end ratio question 3.78 vs 3.56
 

old31,
Sorry, maybe I did not explain well enough. My concern is that with the taller gears you will be lugging the engine in overdrive. Sounds like you are aware of the issues. If you maintain constant vigil while driving to avoid lugging, you will be okay. Many living near me don't! Ouch! I fix their engines.

My previous post was relating what works good for me.
Good Day!

Re: Touring rear end ratio question 3.78 vs 3.56
 

Just to round this out a little, I'm putting a 3.54 in one of my Coupes for a variety of reasons. First is Gas mileage. The A is a real gas guzzler compared to modern autos, so I'll see a slight return of rebuilding costs over the years. Second, RPMs I am not happy when I'm driving 50 MPH and the engine seems to be screaming for mercy, Intensify that for 60. Yeah leisurely driving at 40-45 is OK and I do a lot of it, but some places in Pa are pretty hard to get to without a highway to drive on. Third, I've been advised to install a 3.27! No! Pa.s got too many hills to go that high, 3.54 seems like a good compromise. My engine has a "Something" (?) head on it, B Carb and a lightened flywheel. It seems to have the power to handle the rear.
Terry

Re: Touring rear end ratio question 3.78 vs 3.56
 

Thanks Dave.

Re: Touring rear end ratio question 3.78 vs 3.56
 

My '31 original roadster has a late B block. That I was told was placed in the car in the early 50's. I think a 3.54 rearend was added too. The car will cruise at 50-55 no problem. The brakes are all new and work good. But,
I have to keep reminding myself: "Do not out run your brakes!".;)

Bob-A:D