S4 gearbox in S3

[gt_james]

Has anyone got any experience with swapping an S4 gearbox into an S3?
I am fitting an S4 13B 6 port into my S3, I would like to use the S4 gearbox as the original 12A box is noisey/worn and the S4 has much lower mileage. From what I understand changing the tail housing is fairly straight forward, but I am concerned that it will end up over geared as the diff is 4.1 in an S4 but 3.9 in my S3. Also which speedo drives should I use?

[ian65]

use the S3 speedo driven gear and drive gear in the S4 box

[TOOL]

I have a S4 box in my red RX2. It works fine with my 3.9 LSD. The gearing is better in the S4 box.

It's about 10mm longer than a S3 box iirc.

[gt_james]

Thanks for the response guys. I will be using smaller tyres than the FC used, so hopefully this will negate the effects of the 3.9 final drive. I will be using the FB tail housing to account for the shifter being further back. What size tyres did you have TOOL?

[TOOL]

195/50R15s on it.

[gt_james]

Ah same as me then