HP/torque vs rear end ratio

Just a FWIW, we put 3.27 gears in many Model-As with favourable results. We are in the mountains here and they perform just fine. The key to this is a properly "spec-ed out" engine as several have offered above. I might also add that two of my Model-Ts have a 3.25 rear gear ratio with less horsepower, and we tour with them too.

I suggest you do not based your opinions off of speculation or "He said/she said" information. I think it boils down to are you willing to spend the money to "spec out" the entire powertrain combination? If so, you will like it but life is about taking risks to obtain rewards in my view.
 
I agree with Brent and wish I had a set of 3.27 gears.
When I was coming home on leave, the rear end went out in my Corvan and I was stuck in a small town in the middle of Kansas. A woman had sold the engine out of her Corvair and I was able to buy the differential for only $10. So, I wound up with a 3.27 ratio instead of the original 3.54 ratio. I could notice the difference right away, but it was never a problem.
 
Logan said:
I wouldn't say the front end picks up off the ground. But you can feel it getting a little light. It's pretty sketchy going that fast in one even with hydraulic brakes. I only did it once just so I could say that I did it.
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Actually I was exaggerating for effect. I think the real number is about 100 MPH but watch out for side winds at any speed over 55 MPH. Anyone here on the barn ever had this happen?

Charlie Stephens
 
Logan said:
I wouldn't say the front end picks up off the ground. But you can feel it getting a little light. It's pretty sketchy going that fast in one even with hydraulic brakes. I only did it once just so I could say that I did it.
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I run a Phaeton with an internally modified "A" engine, standard rear end ratio and a Mitchell 26% overdrive. With the top up, on the interstate, anything over 70 mph and the front steering gets real light to the feel and the seams between pavement slabs are not felt. It feels like you have "air" suspension...which I am sure you do. With the top down 78 mph still feels normal. All I know is any speed over 65 mph one can not physically maintain for very long as your white knuckle fingers starts to ache! I much prefer 40-45 mph and the view with 10 to 15 other Model A's out in front of me during a Club tour.
PC/SR Your calculation matches mine...15.6% more power(torque) needed at all given rpms you attack the hills at.
Good Day!
 
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Okay, I decided to compare the torque of the two engines by visiting the website mentioned above.

***Note that the hi-comp head is a 5.2:1 not the 6:1 which would have provided better results.

Torque comparison of STOCK A engine (30 DEGREES TIMING) and SNYDER HEAD 5.2-1 COMPRESSION, B CARBURETOR, MANIFOLD BORED OUT TO B SIZES , ARIES MUFFLER (28 DEGREES TIMING)

rpm STOCK MODIFIED
1200 129.70 144.26 11% more
1300 127.01 142.64 12% more
1500 123.78 143.72 16% more
1700 111.94 141.03 26% more
2000 100.64 129.19 28% more
 2200 91.50 120.05 31% more
2500 74.82 103.37 38% more
2700 62.44 97.99 56% more


 
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I'm no expert, so I could be wrong...looking at the above torque comparision it seems that a 3.27 car with a 6:1 hi-comp head, B carb, bored inlet and an Aries should match a standard engine car with 3.78 in the hills. What do you think?
 
M2M said:
I'm no expert, so I could be wrong...looking at the above torque comparision it seems that a 3.27 car with a 6:1 hi-comp head, B carb, bored inlet and an Aries should match a standard engine car with 3.78 in the hills. What do you think?
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You'll do even better with a wise choice in a cam. :)
 
M2M said:
I'm no expert, so I could be wrong...looking at the above torque comparision it seems that a 3.27 car with a 6:1 hi-comp head, B carb, bored inlet and an Aries should match a standard engine car with 3.78 in the hills. What do you think?
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M2M...You got it! Your data shows it...Somewhere between 1500 and 1600 rpm and greater you are correct. Below 1500 rpm even with the 6:1 head you may have slightly less power when driving hills than your base engine and current gearing. I do not have the data to back it but I think the torque gains below 1500 rpm when running a 6:1 Snyders vs a 5.5:1 Snyders may be minor. As Marco says...a good cam will really wake up the engine response.
I think overall you would be satisfied with the change you are contemplating. Study the data and trust it. Good luck with your project.
Good Day!
 
M2M: Good job on the calcs. So, using one of the handy-dandy online calculators, at 1600 rpm, and 30" tires, speed with a 3.78 is 38 mph, with a 3.27 is 44. A 3.54 would be 40 mph. Are there hills in Australia? (Just kidding!) I think the torque numbers would be a bit better with an HC head and single downdraft carb. Add a mild cam.....
 
It's easy to OVER gear & be sorry for it, but some will NEVER admit they made a BAD CHOICE! It's easy to get caught up in the bigger or higher is BETTER. Bill W.
 
BILL WILLIAMSON said:
It's easy to OVER gear & be sorry for it, but some will NEVER admit they made a BAD CHOICE! It's easy to get caught up in the bigger or higher is BETTER. Bill W.
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Yes, I agree Bill. That's why I'm interested to hear what people have to say and to look at the dyno results.

I suspect the answer to whether a 3.27 works well in the hills depends on the hills and what speed you are doing.

Hitting a long steep hill at 40mph, the warm engine 3.27 car will do better than the stock car with the 3.78.

On a narrow mountain road with steep hairpin bends the 3.78 stock car will likely do better.

 
wow this sure is getting emotional. Is everyone taking their meds?
Why not add a period McCullough blower and remove the body entirely for a better HP-to-wt ratio as well as all the other modifications and let'er rip. And everyone knows how safe it is to drive an A over 60. And heck those babbitt bearings can stand up to just about anything. And if not why not just add a pressure-fed oil gallery from JC Whitney
 
Hey Tony: You are really a fun guy. Thanks for the comments which clears everything up just when I thought this thread was done. Too bad you did not come in at the top of the thread and save all the rest of us the time and effort of the comments. But just for the hell of it, and it is late, I bet my 3.54 beats your 3.27. Flathead, right?
 
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I have a 3.54 rear and completely stock otherwise with a Model "A" Zenith carb, ran that way for 20 years. About 6 years ago we rebuilt my engine .040 over, Brumfield 5.9 head, Stipp IB30 cam , modern valves (cut with 3 angles), and poured bearings. Still running Model "A" Zenith carb. Per Bill Stipp I should be getting around 56 HP, I don't know about that but the improved performance is really remarkable. Put about 7,000 miles on the "A" which included driving thru the Maryland and WV mts. in 2010 to French Lick National meet. This spring added a Michell OD (26%) and drove to Oshkosh in the summer and Chattanooga, TN in Sept. Put about 7,000 miles on it this year with the OD, which included the mts. in PA, MD, VA & TN. No problems with power, the car ran great. Runs cooler and gets about 22 MPG, and I can drive all day long 50-55. Also in OD the car runs very quiet at 50-55.
 
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