Fuel grade in A6 4.2 quattro Digest, Vol 78, Issue 29

[Scott]

The 4.2 is a normally aspirated engine.

Not a turbo.  Unless towing, hot climate & working hard up hills with the AC on, no need for more then 87/89 octane, is driven mildly around town / highways.

IF you expect all horses to show up on the run from the stoplight or while full with people entering the freeway, they rated the motor at optimum conditions and
the recommended octane: Premium.

Probably playing with fire in a small turbo motor if you can't lay off the go pedal......................

I run 87oct in all my turbos and when I expect more (track event / boosting up hills in 90 degree weather w/ AC ) I switch to 91/93 octane three tank fulls ahead on an event.

99 A6 Avant 87 octane 196K
91 200 20V turbo 187K
99 A4 1.8T driven by grandma 87 octane: 88K
many other daily drivers...........................no engine repairs.

Oil, filters (air & oil) and injector cleaner more important.

YMMV.

-Scott by BOSTON