I shifted the motor at 6000 in first and second gear and went threw the traps at about 5400 rpm.
The 3.91 gears are perfect for the combination i have ,if i run a 26 inch tall tire.
The 7 1/4 rear won't handle slicks though.
The 8 3/4 has a 2.94 gear set in it.
I also have a set of 4.56 gears in a 489 case with welded spider gears.
I will be buying a spool for the 4.56 gears, and will run those too.
I will be using a 28 inch tall tire, and when used with 4.56 gears will add only about 400 rpms to my trap rpm.
If i ran 4.56 gears with a 26 inch tall tire it would be to much gear for the motors power band.
At 5800 it will be just past my peak horse power and will run the fastest due to my 60 foot short time being improved ,and it will give me more mph.
The 2.94 gears will be slower but the cam and converter are perfect for both gear sets.
The bigger tire will help with traction with the 4.56 gears.
The bigger tire will help in a different way with the 2.94 gears, since i will only be using 1st and 2nd gear,so i need to keep the rpm's down and this will do just that.
When racing with the 2.94's, i will shift at 6200 and go threw the traps a little over 6000 rpms.
Thank you for your reply's and we will see who's the closest on the ET guess.
This might surprise some people in the end, at what you can get out of a set of highway gears when run as a two speed, and also when you rev a pretty much stock small block up and keep it wound up the hole way threw the traps.8)