The gearing he is talking about is from the JDM ITR Spec R motor. I put this tranny on my friend B18C, and it really does help with acceleration, and the B18C is a joy to drive.

The FD (Final Drive) ratio i believe is 4.7, not 4.9. The 4.9 is the ATS final drive. I presume, I don't follow it too much.

Anyways. For turbo the gearing is too short. You'll accelerate quicker but you won't hold the boost as long. You'll go through the gears too quickly. I personally like the GSR gearing better for turbo, but others perfer LS (even taller gearing).

I'd advice against putting the 4.7 FD in your car if you are gonna turbo.

BTW I have the grind, same as you. If you are gonna go for a rebuild go with GSR tranny replacement parts, or you can look at custom gearing from Kaaz, but the are very expensive.

L8r