Mitchell Overdrive
- Thread starter Bob Grieb
- Start date
Bob,
I changed the rear end in the Coupe from 3.54 and NO OD to: 3.78 and a 26% OD. I REALLY like the change from the 3.54.
Power is better, pulls hills much better now. Henry's engineering on selecting 3.78 was sound!
The coupe has had 6.00 16s for last 10 years (10,000 miles).
The 3.54 had been in the car since 1989 (I took out 4.11s which I put 41000 miles on the car with).
I liked the slower running engine (with 3.54) at 55 to 65, But it always lacked power on long hills at 8000 to 12000 feet.
Also I have had "the 5.2 CR "head with the Large B" AKA Police head for over 50 years.
The Higher compression head gives the most "bang for the buck" and is easier than changing cams, bigger valves and such.
With the 3.78 and 26% I now have the best of "both worlds".
At 60 MPH shifting into OD HIGH the RPM drops from about 2700 to some where around 2100. (The RPM figures are from memory) GREAT I love it!!!
My thought is that 36% Overdirve IS WAY too high for Model A. It MIGHT work with 4.11s.
ADDITIONAL INFO:
I should say that this is a B block with 10,000 miles on the rebuild.
Cam is an unknown regrind that Mike Rickter put in engine in 1989. Mike is not around anymore to ask details.
Carb is one of Berts Model A Zenith rebuilds.
I changed the rear end in the Coupe from 3.54 and NO OD to: 3.78 and a 26% OD. I REALLY like the change from the 3.54.
Power is better, pulls hills much better now. Henry's engineering on selecting 3.78 was sound!
The coupe has had 6.00 16s for last 10 years (10,000 miles).
The 3.54 had been in the car since 1989 (I took out 4.11s which I put 41000 miles on the car with).
I liked the slower running engine (with 3.54) at 55 to 65, But it always lacked power on long hills at 8000 to 12000 feet.
Also I have had "the 5.2 CR "head with the Large B" AKA Police head for over 50 years.
The Higher compression head gives the most "bang for the buck" and is easier than changing cams, bigger valves and such.
With the 3.78 and 26% I now have the best of "both worlds".
At 60 MPH shifting into OD HIGH the RPM drops from about 2700 to some where around 2100. (The RPM figures are from memory) GREAT I love it!!!
My thought is that 36% Overdirve IS WAY too high for Model A. It MIGHT work with 4.11s.
ADDITIONAL INFO:
I should say that this is a B block with 10,000 miles on the rebuild.
Cam is an unknown regrind that Mike Rickter put in engine in 1989. Mike is not around anymore to ask details.
Carb is one of Berts Model A Zenith rebuilds.
Last edited:
MrBruce
Senior Member
I'm looking at the same thing. I have run 3:54's for the last 25 years and some said to keep those and run the 26% overdrive. I'm a little concerned that it is to high. I am looking at going with 3:78's and the 26% overdrive. I was wondering what the RPM would be and you answered that question. I thought it would be lower than that, but anything around 2,000 RPM would be good.
TerryH
Well-known member
I agree.....I also have a Town Sedan, with 3.78 and 26% OD, along with HC head. The Town Sedan is the heaviest of the passenger Model A's, and the HC head works very well with the OD. I can even pull modest hills in OD. A higher rear end ratio will have a hard time pulling the OD, without some significant power increase......best all around is the 3.78 and 26% in my opinion.
The 3.78 and 26% is probably a good choice for you in Colorado. I run a 3.54 with a 23% Ryan overdrive in my stock '30 Tudor with a Snyder HC head and it does fine. yes, on hills I have to shift sooner but that is expected and you will as well.
I have driven my Tudor in and to Colorado a number of times including climbing Pikes Peak and other passes... my combo did great.
I would stick with the 26% in my opinion with the 3.78.
Larry Shepard
I have driven my Tudor in and to Colorado a number of times including climbing Pikes Peak and other passes... my combo did great.
I would stick with the 26% in my opinion with the 3.78.
Larry Shepard
CWPASADENA
Well-known member
I have 3.78 and 26% O.D. in my 30 Tudor. 19 in. wheels and a "B" engine.
Really works well. Would not change anything.
My experience.
Chris W.
Really works well. Would not change anything.
My experience.
Chris W.
inex01
Senior Member
Steve I completely agree with you, my 31 Sedan currently has the 3.54 and 26% OD and I do plan on swapping the 3.78 in my stock Roadster with the 3.54.
I have driven the car with this setup for the past six months. Around town without the OD she runs well but as you mentioned on the road it will "Lug" unless on level ground. My engine has the 5.4 head with a touring cam although the engine is strong but not strong enough with this gearing configuration for my heavy Town Car (2,550 LBS).