Always Red Dave

Ok let me try it this way does anyone think having option GU2 2.73 performance axle ratio makes the C6 faster and stronger than standard 2.56 axle ratio gears on 2008-2011 LS3 automatic cars? Is there as much difference as C5 cars that had 2.73 axle ratio standard gears and 3.15 performance axle ratio option? I had both on different C5 cars that I owned and I always thought the automatic cars with the A4 and 3.15 gears felt stronger and faster than the standard C5 2.73 gears. Is there as much difference on 2008 and up C6 LS3 cars with the 2.73 gears compared to the 2.56 standard gears?

jpuli28

Its not worth the cost difference 2.56 to 2.73. The 2.56 has a differential all its own, you have to change out the diff to upgrade gears. You cant just swap gears.
Now once you have a 3.15 (and a new diff) and want to upgrade to 3.42 then all you have to do is swap gears and keep the housing.
Btw, my 07 LS2 A6 has 2.56.
A taller gear (3.15) is quicker off the line but wont have the top end a lower gear (2.56) has. But in small increments such as 2.56 to 3.15 its worth it. Ive heard alot of guys going 3.15 and later wishing they 3.42. I believe the Z06 has 3.42.

glennhl

The A6 is a different animal than the old A4, so let's equate everything back to the A4 with the one to one 3rd gear ratio. Since the A6 has a 1.53 3rd gear, the 2.56 is equivalent to an A4 with a 3.92 rearend, so it's already darn stout. The 2.73 A6 is equivalent to an A4 with a 4.18 rearend, so it's even stouter by 6.6%. Not a huge difference, but some.

The A4 with a 2.73 is 30% less than the stock A6 and even with the 3.15 performance axle it is still 20% less than the A6. But here's the real kicker. Since autos have torque converters, the 2.73 is still an excellent performer. However, if you are making an A4 into a drag car, most people go with 3.73's which is still less than the stock A6.

The truth of the matter, I doubt that you'd see a .1 of a second running the 2.73 versus the 2.56 A6. Subfloor may pipe in, he went to 3.42's and I'm not sure how much he picked up in the 1/4 mile.

Always Red Dave

Thats what I am curious about the STOCK 2008-2011 A6 cars 2.73 performance axle option GU2 versus 2.56 stock standard axle ratio. If you say not even .1 difference then maybe thats why only 2 cars out of 1003 base verts in 2010 went with GU2 performance axle ratio option! I still remember almost EVERYONE wanting the C5 3.15 G92 performance axle ratio option on a stock A4 C5 cars.Thanks for the advice.

knkali

might feel a little more snappy. Cost of this would make it or break it for me. I had 315,s in my A6 and it changed the personality of the car. It made my eyeballs flatten off the line. I dont think the difference would be much though.

mack morrow jr

Really depends on what you want from the car. The lower gears 2:73 vs2:56 will give you a quicker get off the line and overall faster acceleration, more engine wear and use more gas. The reverse is true for the 2:56.

HOXXOH

If you are talking 1/4 mile performance, the 2.56 is the better of the two. The 2.73 has a slight advantage off the line, but must make the shift to 4th while the 2.56 can finish in 3rd.

Most of the 2.73 gears were included in the Z51 option, which was also handicapped with extra weight.

For street use most people can't tell one from the other.

jpuli28

I priced it...$2600 for the upgrade 2.56 to 3.15.

Sure the 2.56 will finish with a higher mph but will it finish first?

thesubfloor

Or you could upgrade to 3.42's from a C6 Z06 for about half that much.

jpuli28

You could as long as you have the replacing differential case. Nothing other than the 2.56 will fit in a 2.56 case. Dont forget new mounts.

Hey sub didnt realize it was you, thanks for the help in my older gear thread!

jpuli28

Heres an old thread Im holding onto for when I make the switch, hope it helps...

http://forums.corvetteforum.com/c6-c...-to-3-15s.html

http://forums.corvetteforum.com/c6-t...converter.html

bosco 08

My 2.73's were $395.00


Seems to me $395.00 for a tenth or two is a good buy.

BSE1956

I have the 2.73's and it's fine. I'm sure the 2.56 standard gearing would be fine too.
Maybe there's a little more snap off the line, but I think that the 2.73 is more real-world gearing for where I live. I live on an island where the top speed limit is 55, even on the expressway. At 70mph, the 2.73 revs about 90 rpm higher than the 2.56.
Here's a good chart for comparisons of all transmissions. Good Luck.
http://mysite.verizon.net/foofoo2/c6/

peter pan

Glad we ordered our with that option as the chart below shows the less than 100 rpms at 70 mph, was a great choice to get this option from the factory.

Thank you for the chart and it makes our decision to get the 2.73 from the factory a wise choice for the $$

C7/Z06 Man

I had a stock at the time A6 2010 GS that comes with the 2.73 & approx. 4,000 miles on the odometer. I raced a stock 2009 A6 coupe with 20,000 plus miles on it so it was broken in and the drivers were about the same weight.

He ran a 12.7 on that pass and I ran a 12.5 but he did have a slightly higher mph.

JoesC5

When I ordered my '98 C5 A4 the optional 3.15 gear was $100. Absolutely the best bang for the buck. With the A4 and the 3.15 you had a final ratio of 9.639(in first gear).

The C6 with an A6 and the 2.56 rear gear has final gear ratio of 10.394(in first gear) and the A6 with a 2.73 rear gear has a final ratio of 11.08(in first gear).

As you can see, the A6 with the 2.56 is better geared for acceleration the the A4 with a 3.15. If you have a choice between cars, I would go with the 2.73 rear gear, but if I had a A6 with the 2.56 and wanted more dig, I would bypass the 2.73 and jump to the 3.15. The cost to convert to either a 2.73 or 3.15 would be the about the same. Your A6 with a 3.15 would give you a final ratio of 12.789(in first gear). No way would I go with a lower gear ratio then a 3.15 for a regular street car on street tires.

Be ready to see you gas mileage drop with the 3.15's though. Always a trade off.

RicK T

It's because the GU2 was not an option on base coupes and verts after '09. If you look at the 2010 production numbers is also shows 86 coupes got the GU2. Since the GU2 was offered only in GS's since 2010 I can only speculate those 88 total base cars that show with the GU2 must have been some special event cars.

Gearhead Jim

IIRC, GM said the 2.73 did not improve 0-60 or 0-1/4 times, but made the car quicker in intermediate speeds like passing.

All I can say is that our 2009 with 2.73 has only 36 hp more than our 2006 with 2.56, but it feels like at least 50 hp more.

Always Red Dave

Good point I did not understand why the corvette black book did not have GU2 listed as a option for 2010 that is why I went to the corvette action center to get some figures. So I guess from 2010 and up you get a grand sport you get 2.73 in the A6 or if you get a base vette you get 2.56 gears in the A6. NOW I UNDERSTAND.

HOXXOH

Apparently yes quite often. Look in the fast list for stock and bolt-on A6 times. If there is not a specific gear listed or the Z51 option, then the default is a 2.56.

The 2.73 geared car has to shift to 4th and into the low end of the power band to finish the 1/4. It never has time to build and utilize much power after the shift. Even if the shift requires an identical time to complete as a 1-2 or 2-3 shift, the higher speed at which it happens means the car travels farther while in process at reduced power levels.

Meanwhile, the 2.56 car goes through the traps at the high end of 3rd gear without time consuming shifts and during the peak of the power range.