S8 Vs A8 engines

[Richard Hoffman]

For the 4.2L 40v motors...
I believe that Audi bumped up the compression from 10.8:1 to 11.0:1 with the
S8 and also added some bigger cams.  The S8 makes peak torque at 3400 rpm
whereas the A8 makes peak power from 3000-4000rpm
Also, the S8's peak torque is 317 ft-lbs of torque compared to the A8's 302
ft lbs. The S8 motor revs to 7000 rpm where the A8 revs to 6000 rpm.
I believe that the major difference in the horsepower output comes through
the increased rev range - the S8 breathes better at high rpm and can simply
produce more overall power.  Note that the torque ratings are only
marginally different.  Of course, the cars doubtedly have slightly different
ECU programming.
I imagine that upgrading these 40v V8s in any way is an expensive prospect.
If the A8 in question is model year 1999 or older, it has a 32v V8 and I
have actually found a supplier for cams (other than MTM at $4000 for the
set) located in Belgium.
I would wager that working with a 4.2L 32v is much cheaper than the 40v when
it comes to making power.
Hope this helps!
Richard
1990 CQ 214K
1970 100LS 2-dr 46K


>From: ScottyCBoy at aol.com
>To: quattro at audifans.com
>Subject: S8 Vs A8 engines
>Date: Sat, 1 Feb 2003 14:54:29 EST
>
>--
>[ Picked text/plain from multipart/alternative ]
>Hello,
>
>Does anybody know the differences between the S8 and A8 engines, ie
>camshafts
>compression ratio displacement etc??
>
>I guess what I'm getting at is it possible to turn an A8 engine into an S8
>engine by replacing available internal componets like cams, or heads?
>
>SCott


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