Putting an A8 Transmission in an S8

[Mr K]

Originally Posted by mattsimis

I cannot visualise why different ratios on the Rear diff would make its "incompatible" with a different gearbox.. any thoughts?

the front diff is built into the gearbox, change the gearbox and your changing the front diff. If the front diff isnt the same as the rear your front and rear wheels will be going at different speeds.

To be honest, I expect the actual gear ratios within the box are the same, and audi final drive for the A8 and S8 to give the differences.

If your doing this for MPG, I would think about how long its going to take to get the pay back for the new box. Also my s8 (with an S8 gearbox/diff) averaged about 29mpg in both directions on the 600mile round trip to the lake district a few months back, cruising at a steady 70. most of the time I get 20mpg. my mate who had a PF A8 4.2 got about 22-24mpg on average. Bassically dont fit this gearbox if your expecting 30mpg out of your car afterwards, I would expect 1, maybe 2 mpg more?

[Singh]

With the exact same driving style I get 30/1 MPG from an A8 but only 24 on an S8. I think it's the biggest flaw on the D2 S8, there should be a motorway cruise setting that drops the revs by 1K at the flick of a switch.

[Mr K]

Originally Posted by Singh

With the exact same driving style I get 30/1 MPG from an A8 but only 24 on an S8. I think it's the biggest flaw on the D2 S8, there should be a motorway cruise setting that drops the revs by 1K at the flick of a switch.

Fair play - really didn't expect it to be such a big difference!

Wish I got 24 from my s8!

[mattsimis]

Originally Posted by Mr K

If your doing this for MPG, I would think about how long its going to take to get the pay back for the new box.

Nah, that would just be an acceptable trade for the slower acceleration. I was asking the question as A8Parts are selling a good A8 gearbox that they said would fit the S8..