3.55 or 3.73
 

It's been awhile since I have been on PT and longer since I have posted. I am not the builder of my car and the car has been pushed aside for awhile now. It's time for some forward progress. I know what my builder wants but would like to get everyone's opinion about a rear gear. Have a 1969 Firebird. Will be a street car and would be fun to take it to the nearest road track a time or two (Bowling Green). Will have a Ford 9 inch (DSE), 31 spline, 335/30/18, T56 Magnum and probably 600+hp. I know there are several calculation sights out there to help me with a set up but wanted to hear from all of you. 3.55 or 3.73? Please educate me.

Thank you for your time.

Ron

3.70 is perfect with a T56. Make sure you get the 2.66 1st gear in the Magnum.

For sure the 3.70. I had 3.50 gears in my '67 with an LS/T56 and 6th gear at 70 mph lugged around 1500 rpm. You'll been much happier with 3.7x gears.

370 or even 390 with a 6 speed.

Agreed, I had 3.73 with my t56 and rarely got it into 6th. Ended up going with 4.10, partly b/c going 25 mph in my hilly neighborhood left me right at a point where I was constantly shifting.

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4.11 on my T-56.. power band is perfect.

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Should I go with a 5 speed instead?

The t56 gives you bragging rights, but unless you're putting down tons of power a 5 speed is perfectly fine for street driving and will save you from having to cut the trans tunnel in most cases.

I have a TKO 600. IMHO I would of never used the 6th gear. 5 speed and 373 gears with the .064 overdrive and your good to go.

Any low lugging rpm's with the 4.11?

What do you think about aT56 with a 4.56 rear gear and a 2.96 tranny gear?