Looks like it's time for a Dana

[Supershafts]

A mopar Dana 60 uses the same diameter axle shafts as the 8.75 with the exception of length issues.

http://board.moparts.org/ubbthreads...=5929697&Words=+HemiDart68&topic=&Search=true

The D-60 uses 35 spl axles (cars SF) and still has LS options at 35 spl where other diffs do not and instantly jump to spools.

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Who makes the 33 spline if I may ask? Didn't know there was an optional shaft with a TT

Eaton, the same company that made the TT you have now in 30 spl.

Any custom axle company will make 33 spl, i use MW mostly because everyone else plays game with splines so you have to use their stuff or play with them.

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[Wookie316]

But what about a 4500 pound car? Is that going to be enough?

 

[Hemirunner]

Put a ford 9" in it.

 

[Supershafts]

Look at it like this, you have 600ft even if you have the same 1st i do 2.7 that puts you just over the 30 spl capability by 300 ft.
If you have the 2.4 1st you're right on the number and why you aren't having a major break within 2 or 3 passes.

At 33 spl and my 1st and my final of 4.8 you're just below the 33spl by 300ft.

You have 3.9 final though so that puts you at 2000 ft below the 33 spl limit.

The 9" has a odd issue at 33 spl kinda the same issue the 8.75 has at 35 spl, you don't have many LS options at 33spl but can go to 35spl.

Your issue is the axle is the wrong spl for the output, changing the entire diff for another is your decision.

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[Wookie316]

2.87 first.
There must be a formula for figure this out would you share how you come up with these #'s?
Much appreciated

 

[Supershafts]

times your hp by 2.87

 

[Wookie316]

Right now I'm at 1487. But after the head work is done this winter I should be in the 600-620 hp range. That takes me to 1779. What is a 30 spline rated too?

 

[Supershafts]

6200, 33 is 8300

 

[383man]

Its also because its a stick car as the manual cars are hard on drivetrain parts. Years back I raced a 340 Dart that ran a best of 11.94 @ 113 and had an 8-3/4 rear. And it was a stock 833 four speed and I ran 28 x 9 slicks. It twisted the splines alot on stock axles as I knew it was bad when I could not get the axles to go back in. It also broke a few driveshafts and ring & pinions. My 63 runs 10.70's @ 125 with an auto and still has stock axles in the 8-3/4 and they have not twisted. I use a Dynamic 9.5 converter that flashes about 4200 and I come up on the converter to about 2000 rpm at the line. The auto does not shock the drivetrain like the stick does. I loved racing that four speed Dart but I am glad my 63 is an auto as it is much easier on parts. Ron

 

[Supershafts]

You're below the axles rating, and don't have his 1st gear, you're probably somewhere around 5900 with your 1st, final and hp.
Tq twists axles regardless of trans style, and slicks help, drag radials would be harder