Differential Gear Changes

[decooney]

Art, not to debate... but I've tried all the ratios mentioned in my car and friends cars. A Cobra is a different beast, light weight with a big block. I understand the physics and mechanical advantage of lower gear ratios. All great in theory, but its not always accurate on outcome. To me, there is a point of deminishing return when it comes to the torque multiplication factor and rear tire spin. Super low rear gears are not always better in my book. For exampel, there are many people even in drag boating that have produced better ETs by going with "taller" gearing, when using big torquey motors... In a light weight car with a torque monster motor it makes a difference. More importantly, I am saying that I've driven and compared them too side by side; not just talking from theory and physics of mechanical advantage from ratios.

In fact, I can go further to say that if two Cobras were side by side with 4-speeds wide ratio or close ratio setups, with equal 428s at 500HP (0-6000rpms only), one having a 4.11 rear and the other having a 3.31 rear, the one with the 3.31 gear wins stoplight to stoplight heat every time. I've compared this myself on more than a few tests with friends who had lower rear gears and shorter 1st gears. They are shifting gears from 1st to second, blasting the rear tires off while I'm pulling a tad longer first gear that gives me a car length every time. In a heavy Camaro, Mustang, Chevelle, etc... sure, 4.11s are great. In a light weight Cobra, with a 500HP 428, the longer 1st gear will get the jobe done almost every time.

For my car, with a custom wide-ratio large spline toploader, I believe that 3.31 is still just a tad low (with wide ratio 4speed) and a 3.08 is a tad high for an ERA at 2550lbs. 3.08 maybe good for a lighter weight Kirkham or lighter replica. A 3.23/3.27 would be perfect for my ERA and the 428 setup. If you have a friend to compare to side by side with the same motor, him having the taller rear ratio in his Cobra, race him from a stop light and see what happens... just passing along my first hand experience and comparisons. If your motor revs 7500-8000, then I could see where 4.11s might be usable.

Hence, your original question.