Need help picking rear gears

**98TransAmWs-6** · 09-09-2016, 01:30 AM

So I'm trying to decide on what gears to run in the rear. My set up is a built 421 stroker with a built 4L60e. I'm running race tires 26" in the front and 28" out back. I was thinking either 3.55 or 3.73 but I'm open to suggestions. This is for a 8.8 rear FYI.

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**Whamhammer** · 09-09-2016, 06:47 AM

Originally Posted by 98TransAmWs-6

So I'm trying to decide on what gears to run in the rear. My set up is a built 421 stroker with a built 4L60e. I'm running race tires 26" in the front and 28" out back. I was thinking either 3.55 or 3.73 but I'm open to suggestions. This is for a 8.8 rear FYI.

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By going with 28 inch tires, you a making the final drive roughly 8% taller, over the stock 26 inches. The 3.73's, a comparative 3.5 final drive,put you a smidge shorter than the factory 3.42's. You probably even go witb 3.90-4.11's.

**35th-ANV-SS** · 09-10-2016, 03:25 AM

It's too early for me to figure it out, but you should pick the gear that will have you in your powerband in 4th crossing the 1/4 mile mark. I wouldn't suggest a low gear like a 4.10/4.11 though for a 4L60E.

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**98TransAmWs-6** · 09-10-2016, 03:40 AM

That's the thing I don't know lol, I haven't ran the engine in the quarter yet. My power band is up to 7000 rpm though.

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**35th-ANV-SS** · 09-10-2016, 03:45 AM

There's a way to calculate it based on your rear end gear, transmission gearing, and tire size for your combo. I thought there were online calculators even which get you close because I remember looking at it when I got my 9". I'll say that with a 4.11 gear in the T56 and having a power adder like a supercharger, 1st and almost 2nd gear is useless except for when you're racing or wanting to get off the line quick.

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**Whamhammer** · 09-10-2016, 12:19 PM

Originally Posted by 35th-ANV-SS

There's a way to calculate it based on your rear end gear, transmission gearing, and tire size for your combo. I thought there were online calculators even which get you close because I remember looking at it when I got my 9". I'll say that with a 4.11 gear in the T56 and having a power adder like a supercharger, 1st and almost 2nd gear is useless except for when you're racing or wanting to get off the line quick.

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Its pretty easy to do by yourself, especially with an Excel spreadsheet. Just plug all of the data for the tranny and diff ratios, and you have your final drive. Take the final drive and multiply it by the alpha percentage in the difference of the factory tire height, and you know essentially where you are with stock or previous setups.

**sjgreen6** · 09-13-2016, 06:55 AM

Here is a whole host of calculators to figure out your automotive questions. Wallace Racing - Automotive Calculators also take a look at Racing Calculators - TCI® Auto