Good morning ...
I am building a sr20det datsun gx coupe for 1/4 miles
I can get a sr20det only with a 6 speed manual gearbox... ?
Will it work for 1/4 miles....??
Do you get a 5 speed gearbox for sr20det..??

Tanx

4 speed will be quickest, but they don't come with 4-speed boxes.

Only S15 motors came with six-speed

S13 and S14 SR20DET came with 5-speeds

So my best options will be the 5speed ?

Both gearboxes aren't that great for drag racing. If you want manual still? Their are adaptor kits worth looking into for rb25 or z31 boxes

If its only for drag racing your best gearbox is a 3 speed auto

Tanx for all the info

If the 5 speed is just the overdrive from the 4 speed, then it doesn't make a difference. What does make a difference is each gears ratio, your rearend ratio, the diameter of your tire and your RPM's when you need to shift. That will determine what your speed will be at each shift. Use a gear ratio calculator to determine all of this. You can find one on the net.
After that you can manipulate the tire size and rearend gear ratio.