what gear to use in 9 in

Depends on the motor and the first gear ratio of your tranny. If you have a small motor with a big cam (no low end power) with a close ratio 4-speed (2.32 first gear) and a 2.79 rear end you are going to HATE it.

On the other hand, if you have a big inch (350+ motor) with decent low end power and a wide ratio tranny (2.78 first gear) then a 3.25-3.50 will make you happy.

I have a 347 that likes to rev although it makes decent power about 2000 rpm. I have a 5-speed with a 2.95 first gear and 3.89 rear gears. I love it. However, if you do not have OD then anything above 3.25 gets old fast on the highway.

If I had a wide ratio 4-speed and drove almost exclusively in town or on the track then I would go with 3.50 - 3.90 gears.