I can't decide between 3.21 or 3.55 gears for my 8 1/4. This car is NOT a daily driver but I would like to drive to the beach occationaly which is 1 hr of highway speeds at 70 MPH. Maybe 65 mph if I don't mind being past every 10 seconds. This car will never drive crosscountry. It'll likely only see the drag strip a few times. Is there a big seat of the pants difference between the two ratios?

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

With your build I would be at 3.91 or 4.11.

With a Comp 264/9.25:1 I rarely get out of 3rd gear under 60 mph. I have to be doing at least 70 to even think about 5th.

To figure ratio: tire size, target rpm(at peak torque), cruising speed.

You also dont want to be below stall speed on the highway.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

What size are your tires? I had a 3.55 in my Barracuda with the A904 after having a 3.23 for many years and I could never get used to the revs on the highway. I was running 205/65-15 tires. If you will be running a taller tire then it won't be so bad. The other problem was that it ran out of Torqueflite's second gear too soon which doesn't give you a good passing gear in the 60-70 mph range. I think Slants like to pull taller gearing to make better use of their low rpm torque peak.

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"Former Owner" of '65 Barracuda, 225, Auto, MP 2bbl intake, MP cam, Dutra Duals. Presently Moparless.

I'am going to be running 26" tires. I am going with a 2500 stall convertor. I found one that will get me by until I upgrade to the more common trans and convertor. I think the 3.55 gear is best for my plans. Not the best power but maybe the best for my plans.

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

Here is a link that may help you decide.

http://www.moparts.com/Tech/tech/img/AUTOMATICchart.xls

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1971 D100 SWB Step side, 225, 3 on the tree, 3.91 gear

B. this is the calculator you want to use

http://users.erols.com/dmapes/CALCMENU.HTM

With 26" tires, I would go with 3.55:1 More fun around town and at the strip but not too bad on the highway.