What kinda car is it going in? And pay attention to what Skep419 mentioned. Torque converter is extremely important for your build. Don't bother with off the shelf. I have a PTC unit special built to my specs and it was cheaper than an off the shelf B&M. As for gears, depending on how far you are racing will determine what kinda gears you want. The shorter the track, the higher (numerically) gears the better. Traction of course will be a problem the higher (numerically) your gearset is.
