Hello Advice needed please, 32 coupe, 284 flathead, warmed over and 3.54 rear. Anyone running similar and what ratio did you choose - 26% or 36% over? Thanks for any advice.
If the Mitchell works like others, those choices would be about 74% and 64% (effectively) of the axle ratio. Doing the math, at .74 x 3.54 = 2.62 effective final drive...... .64 x 3.54 = 2.26 effective final drive. Even the 2.62 effective ratio is pretty tall for your power train and wind resistance. Those ratios would be better utilized with a final drive of at least 3.78 (Ford std ratio) or 4.11..... .74 x 3.54 = 2.80 or .74 x 4.11 = 3.04. And, if you have really tall rear tires, it gets worse, as tires are also part of the equation. Ray
I've got 3.54s behind my 59A, which from what I understand is slightly warmed over, though I didn't do the work. It's still running a single carb and cast iron intake, so not sure how warmed over... Anyway, I put in a Columbia 2-speed to go with the 3.54s, and it's phenomenal. From what I've gathered, and how it drives, seems to be about a .72 OD. It doesn't really bog unless it's a long incline, and it's great for high speed cruising. Plus, the 3.54s mean you don't have to engage OD as often, which is a huge benefit in my book. Just driving around town you don't really need it. With 4.11s (what I originally had in it) I felt the need to use OD a lot more often.
^^^^^^^^^^^^^^^^^^^^what size rear tires are you running? .72 x 3.54 = 2.55. I ran 2.79 geared 8" Ford rear axle in my '47 Ford w/ 255" Merc flathead, '50 Merc 3 speed (Isky cam, 4 bbl Fenton headers MSD ign), 235/70-15 radials, a few years ago. Not at all bad on the highway, but not great for around town stop and go, especially on an uphill incline. I thought a 3.00 would have been a better choice, maybe even a 3.25. Ray
Ray, My rears are 28.8" Diameter. 6.50 - 16's I think, though I'd have to look at them again. I drive a lot so I like a tall gear just to keep the RPM down on the highway and also to chase a little more economy. I used to run a warmed over Ford 289 in an OT Mustang with a T5 in it. Had 3.00 gears, 225/65-R15s, and an OD of .68. Loved how that ran on the highway. I could get 25 mpg all day long, and the T5 was geared well enough that it was still peppy, though no stoplight racer by any means.
I've got a mitchell in my '47 with a mild flathead and 3:78 rear. I went for the 36%, my thought process was that if I'm spending that much for the unit I want the biggest reduction!
We had 3.54 rear gears and a stock 3 speed behind a mild 255 merc flathead and 31” tires we were cruising at around 2500 at 60 mph. We went to a T5 with .72 5th gear on 4.11 rear gears which in effect gave us 2.9 rear ratio at 60 mph bringing the revs down to around 2000 at 60 mph. It has lost a little torque in higher gears as we have an L100 cam . But its just eats up the highway and is a fun car to drive. You need to bear in mind where your engine makes its power. I dont think you want much under 2000 rpm for a flathead at your chosen cruising speed or it will fall on its face and potentially use more fuel.
Thanks, 284 so quite torquey, think the 36% be good for the long drives from Scotland that we have to do.
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