[1320WhtRex]

Woildnt you have to add a gear on the countershaft for the sixth gear?

Yes.. Simply add the 6th main and counter gears on the shafts, use the Type S Shifter Mechanism or modify the 5spd shifter mechanism (http://www.k20a.org/forum/showthread.php?t=16099), and use the 6spd forks. Also the 5spd has the reverse lock cam. The 6spd doesn't. You can just take that out.

 

[1320WhtRex]

What if I just want to change 3rd and 4th and skip adding a 6th? What parts would I need?

1st Gear 3.062:1 36.86 MPH (Stock gear)
2nd Gear 1.769:1 63.8 MPH (Stock gear)
3rd Gear 1.354:1 83.35 MPH (TSX 3rd)
4th Gear 1.027:1 109.89 MPH (TSX 4th)
5th Gear .738:1 152.92 MPH (Stock gear)
Final Drive 4.764:1 (Stock FD)

Then you will need 3rd and fourth main and countershaft gears. That's it.