S8 Vs A8 engines

[Virtual Bob]

> >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?
> 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!

I've heard the S8's has dual-stage intake; A8 has variable (presumely
stepless) intake profile. But by my guess the biggest kick come from the
availability of manual transmission (left hand driver in Europe) or the
lower gear ratio (in the States).

For A8 upgrades, wasn't there an European company offering supercharger
sometime ago?

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