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Old 04-16-2009, 02:42 PM   #8
Drives: '04 GTO, '00 Z28, '95 Z28
Join Date: Mar 2009
Location: Austin, TX
Posts: 225
I'd expect about a 4 mph difference between the M6/LS3 and the A6/L99. Considering the M6 has 26 more HP to play with at the flywheel, that's worth 2, maybe 3 MPH right there. Plus an automatic typically has more losses in the tranny and along the drivetrain, I'd say autos often dyno ~10 HP lower than manuals for the same rated flywheel engine power. So the automatic L99 is starting with less HP to begin with, and getting a lower percentage of it to the back wheels.
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