Looking for more pep off the line

Something not everyone realizes is that tire diameter can effectively change gear ratio. I.e., if the rear tires are 30 inches tall, then compared to the 26 inch height of your front tires, your effective gear ratio is 26/30 times 3.23, or 2.80.

With the right combination of torque converter and tire diameter, 3.23 gears can be pretty quick off the line. The mild 360 in my 67 Barracuda would burn rubber most of the way through low gear with street tires and 3.23 gears (not to mention OEM springs in the distributor, a cam that was just installed dot to dot, and pistons that sat .100 below deck at TDC). (Nitto drag radials fixed that, even when I switched to 3.55 gears.) With enough traction, 3.91's will be quicker, but there's a definite trade-off of high rpm's at cruising speed and loss of top speed. Shoot, these days, even 3.23 gears will have you buzzing at highway speeds compared to today's cars, which can turn less than 2,000 rpm's at 70 mph. Of course, they get by with that because they have many more transmission gears than our old three-speed Torqueflites. With the latter, rear gearing is always a compromise.