Axle ratio selection with T56

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cu440da

cu440da

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I figured this might get more responses posted here rather than the drivetrain section.

Starting to think about rear axle ratios to get a plan in place. I want a steep gear for racing. The double overdrive then making it driveable on the street.

With the T56 1st gear ratio of 2.66, what is the highest axle ratio you would want to go with before 1st became a useless "granny" gear? (For contrast the 727 uses a 2.45 1st gear, and I liked when I had 4:10's in the rear with that setup.)

Now, I am no math wiz, so I dont know how much the calculated difference in 1st gears will work out to be- but it looks slight.

Would a 4:56 rear axle ratio be too much?
 
The problem is driveshaft rpm get nasty in 6th. I have 3.91's in mine and would not go any higher numerically. If I had my way I would love a .80 5th and .62 6th with 3.73's or 3.55's. But still with my .50 6th, cruising at 80mph at 2050rpm is the BOMB. With a set of slicks my car should drag race just like a Hemi 4 spd car with 3.91's.
 
The T56 1st gear ratio you posted is the same as the 1st gear ratio of the pre-71 A833's...
 
Tire size plays into it all as well. The rear wheel openings limit the available tire height without modification. With ~26" tall street tires and a 3.55 rear gear I'm chugging around 1700 rpm in 6th to do 70. When I have my street slicks on that are closer to 28" tall I'm closer to 1600 rpm at 70. All of this is with the .5 overdrive of the Viper spec trans as well. Some of the others have less overdrive like BBSwinger was talking about.

The first gear ratios on most of the aftermarket units were one thing that drove me away from them. Some were just ridiculous like 3.5:1 or worst. The split between first and second was pretty big as well. I guess it's nice for someone who doesn't want to work hard to get a car moving, but that gear would be over so fast I don't see it being useful.
 
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