What final (rear end) gear ratio should I go with?

[RGS0907]

I wish I could run 2600rpm at 70 mph...with my 429 and 3.50s I run 3500 at 70. But then again I have a quater mile C6 with only 3speeds.

That's way to high for 3.50s. You shouldn't be more than about 2600-2800. Even my old 4.11's didn't rev that high. I used to have the formulas to calculate this out, I'll have to look it up at home tonight.

 

[Edbert]

That's way to high for 3.50s. You shouldn't be more than about 2600-2800. Even my old 4.11's didn't rev that high. I used to have the formulas to calculate this out, I'll have to look it up at home tonight.

RPM chart for AOD

Edit: This chart is for AOD only, it shows 3rd (1:1) and 4th gear RPMs. If you have a C4 C6 you should just use the 3rd gear portion. If you have a T5 or Tremec the 3rd gear portion is for your 4th gear.

 

[68DARKHORSE]

You should be using a T5 with 2.95 1st gear.
The 3.35 is weak.

 

[68DARKHORSE]

The 2.95 trannys are also more of a close ratio setup.

You can get a trashed T5 for $50, then build it with Z spec parts. You can also increase the OD to .59.

 

[Kman]

Agree with 68DARKHORSE. The old 3.35 T-5's were marginal in a relativley stock 5.0 mustang making 225 hp at the flywheel, when driven hard. Ford repaired and replaced a lot of these trannys (infamous for third gear problems) over the years. They will last a long time when driven "normally" but with 400hp on tap, some traction and a few powershifts, a long lifespan should not be expected.