I suppose the Cd of a Corvette is better than that of a GTO, they are about 500 pounds lighter also. What is the stock rear end gearing, is it the same as the GTO's 3.46?
The CD of the C6 is .29. I think the GTO is the same or .30. They are real close, but the frontal area of the Vette is smaller, giving it an aero-advantage.
My C6 is a base 1LT model and it weighs in at 3132 with a 1/4 tank. My GTO weighed in at 3740 with a 1/4 tank, so there is about 600 lbs difference or a 16% advantage.
The gearing on the A6 is completely different than the gearing on the M6. You have a hard time comparing them.
That said the rear gears are 2.56. Here is how it breaks down:
A6 M6 overall ratio A6 M6
1st 4.02 2.97 10.29 10.28
2nd 2.36 2.07 6.04 7.16
3rd 1.53 1.43 3.92 4.95
4th 1.15 1.00 2.94 3.46
5th .85 .71 2.18 2.46
6th .67 .57 1.72 1.97
The first to second spread drops the M6 to 4500 rpms at a redline shift. The A6 with the wider spread goes from 6500 to 3800 rpms. Ideal on the 1-2 shift for a stock LS2 would be 4500 rpms. So the 6m is just about ideal on the 1-2 shift. The 2-3 shift comes up at 4200 for the A6 and 4500 for the M6. The 3-4 puts the A6 at 4800 and the M6 at you guessed it 4500.
If you get your shifts exactly right the M6 is the perfect tranny for the LS2.
As far as fuel mileage goes the A6 is slightly better.
I'm still happy though, the car runs consistant 12.4-12.6 at 114 in the 1/4. I could probably do better every once in a while with a stick, but the A6 is deadly consistant.
My best with the GTO at the track was 12.8 at 109 stock versus the 12.4 at 114. Most of the time I ran 13.0-13.1 with the GTO on a cool day versus 12.5 for the C6. They say every 100 lbs = .1 in the 1/4 and about 1mph, well that is the difference between the 2 cars almost exactly.
The GTO was definately more rewarding due to the difficult nature in driving it to it's potential. The C6 is basically a hit the gas and wake me up when I'm done beating up on the guy next to me car.