Rathmullan

Hello:

I am new to this forum and I'm considering the purchase of a 2008-2009 Corvette with automatic transmission.

I have learned that the '08/'09 automatic transmission Corvettes equipped with the Z51 package have a 2.73 rear axle ratio (compared to the standard 2.56 ratio) as well as different transmission gearing ratios compared to the base model.

In '08/'09 the 2.73 GU2 axle ratio was available as an option on the base model. My question is simply this: Do those base Corvettes ordered with the GU2 axle and automatic transmissions have the same transmission gearing ratios as those Corvettes ordered with the Z51 package?

Thank you in advance and I apologize if this topic has been "beaten to death" but I have been unable to find a definitive answer to this question anywhere.

haljensen

There is only one A6 transmission for C6's. The ratios are the same for all C6 A6.

Manual transmissions have a difference. Here's a chart that shows the different ratios;

Rathmullan

Haljensen:

Thank you. But if you are correct, what is the following guy talking about? He seems to be saying that the Z51 auto transmission is different from the base's autotranny. (at least in '08):
"
Paddle Shift
The 2008 Corvette lineup was also offered with an optional six-speed automatic, paddle-shift transmission. This transmission has a first gear ratio of 4.03 to 1, 2.36 to 1 is used for second gear, 1.53 to 1 for third, 1.15 to 1 for fourth, 0.85 to 1 for fifth, and sixth gear has a ratio of 0.67 to 1. The final gear ratio for this transmission is 2.56 to 1. For the Z51 application, the transmission has a first gear ratio of 2.966 to 1, which matches the MZ6 transmission's first gear. However, gears two through six are taller by 12 to 25 percent. An optional 2.73-to-1 final drive gear ratio is available on the automatic Z51.

Read more: 2008 Corvette Gear Options | eHow.com http://www.ehow.com/list_7560245_200...#ixzz2CKz561ZX

haljensen

I would say that the poster you quoted read the charts wrong. The ratios the post gives for the Z51 A6 is actually the ratios for the Manual6spd Z51 and would be very unusual for an auto transmission. A 2.966 first gear with a 2.73 rear gear? That would give an overall first gear ratio of 7.597, the absolute SLOWEST accelerating gear of all C6's.

Rathmullan

Haljensen:

Gottcha. The automobile catalog also supports your answer. So I guess it is safe to assume that the only thing that makes the Z51 Auto Corvette .1 second faster in 0-60 times compared to the base LS3 Corvette is the 2.73 final drive, and a base Corvette optioned with the GU2 Axle (2.73 final drive) would also be .1 second quicker?

haljensen

GM needs a Fact Checker or Editor for a lot of what's published. You can't believe any one source anymore, everybody has an agenda.

Posted times are always questionable. Most aren't actual, they are "adjusted" to sea level, barometric pressure, temp, humidity, etc. Sometimes I think they are adjusted for advertizing reasons like with the GS. Quicker 1/4 times with a heavier, less areodynamic body and the same engine?

Another difference in Z51 to base is the tires, the Z51 Supercar runflat tires are stickier (and wear faster) than the base runflats.

Mike's LS3

Good points and A6 is the only auto transmission offered in 2008-09 as listed in the above charts.

JoesC5

All six speed automatic transmissions have the same gear ratios, no matter what the rear end ratio is(2.56 or 2.73).

Manual transmissions have different gear ratios(depending on the application) but they all have the same rear alxe ratio(3.42).