Originally Posted By DaveRS23
At hiway speed, the difference between 3.91s and 3.55s is a little over 300RPM. That isn't that big of a difference.


http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php


That was my first thought. Approximately 10% difference. Not worth it in my opinion. There is no gear ratio available that will allow you to cruise at 1500-2000 RPM like you are used to in modern cars with 2 overdrives and lockup converters.

Back in the late 60's early 70's many muscle cars from Ford. GM. and Mopar came with 4.10 gears and 26" tires. However a 383 Fury Wagon was not then, is not now a muscle car. It probably had a 2.93 originally. People drive faster now than in 1967. with a 2.93 gear at 75 mph the RPM will be 3000 plus but with no tach and a quiet exhaust system who noticed? 3000 RPM is not going to hurt a 383 unless it is already hurt.

The way I see it a 2.93, much less a 3.55 will not get you were you want to be. Several people have suggested an overdrive transmission. That is the only way you are going to cruise at 70-80 MPH at comfortably low rpms.

ME? 4.30s with 28" tires. Has only been on the interstate longer than 10 minutes at a time once in 20 years. If I ever get around to switching to a Dana it will probably get a 4.10.

In theory, there is no difference between theory and practice. In practice, there is.