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pinto v6 8" automatic rear end ratio

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My 78 V6 C4 automatic Cruising Wagon came with a 3.40 8 inch rear end ratio. About 5 years ago I switched to a 3.00 to lower the rpm on the highway. It dropped my rpm by about 400. With the 3.4 at 65 the engine was at about 3500 rpm , with the 3.00 70 was about 3500 rpm. However, this spring I switched back to my 3.40 ratio. The reason is a now have a camper that I tow. I usually tow between 55 and 60 and would have to downshift to 2nd on hills more often that I liked. The lower ratio keeps the rpm's up. During my trip to Carlisle, it seem to work better.     

The 2.3, T-5 has a .79 overdrive. So that effectively drops RPM 20%. Most people forget but tire size is a factor too. Here are some results with a 3.40 rear and the T-5 .79 overdrive at 65 MPH:

22" tire = 2,667 RPM,  23' tire = 2,551 RPM, 24" tire = 2,444, 25" tire = 2,347 RPM, 26" tire = 2,256 RPM

With 3.00 rear and the T-5 .79 overdrive at 65MPH:

22" tire = 2,353 RPM,  23' tire = 2,251 RPM, 24" tire = 2,157, 25" tire = 2,070 RPM, 26" tire = 1,991 RPM

The 3.40 rear ratio and 26" tire is about on par with the a 3.00 rear ratio and a 23" tire. Also keep in mind lowering RPM sounds good but if you don't have the torque in the motor you are in for a long, slow rate of getting up to speed. As an alternative to the T-5 I'm of the mind set that if you are going for a long drive have a cheap set of steel wheels and very tall tires for getting there. Then swap to your nice matching set once you arrive. You might find a set cheap at a wrecking yard with decent tires for $50-$100.  BTW, this is for "lugnut." I realize "flash041" does extensive travel and toting a spare set of wheels is impractical.

This is the link to the calculator I used:


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