steppindown

In the order guide I see a performance axle ratio available for auto trans Z51 cars.



GU2 Rear axle, 2.73 ratio, limited-slip, performance


However, every price list I have seen does not show this option. I have it on my A6 2008 and do feel it gives a little bump in acceleration.

Any clues?

Bill17601

Yes. The axle 2:73 is included with Z51 with an automatic. There are no optional rear ratios. I asked the same question because I wanted that ratio.

rcallen484

But you can only go 185 mph at Bonneville instead of 190 Watching a program on Velocity Channel right now and a guy who was recently inducted into the 200 mph Club at Bonneville said there are less people in that club than have climbed Mount Everest. And to think that we have most of those people as members right here at CF

Bill17601

My C5 has a 3:15 rear which kept me out of the 175 club which has more members then little league.

JoesC5

Top speed of 190 should be the top speed for both the base(2.56) and the Z51(2.73) as both will be drag limited as they will run out of horsepower, not gearing. The base will hit 190 in 5th gear at 5,175 RPM and the Z51 will hit 190 in 5th gear at 5,520 RPM. Both are along way from 6500 RPM at 190 MPH in 5th gear.

Of course, the straight away at the local Sonic will have to be pretty long to see that speed.

Bill17601

Joe is correct. Speed is a function of horsepower in this case. The lower rear will just get there quicker.

speedlink

I'd love to race at Bonneville someday.

rcallen484

Others say they have experienced otherwise, but at over 165 mph (not at Bonneville) I felt the slightest "float" sensation in mine and lifted immediately. First time I had ever felt that so maybe it is something high speed drivers get used to or maybe I encountered a very slight breeze of some sort.

JoesC5

Not me. Have you seen the salt build up on the cars after they do a run?

I would like to run the 8 mile high banked oval track in Ohio. Coming out of the corner at 160 and then having close to two miles to accelerate down the straights, hitting 198 MPH, before braking to go though the next corner at 160 MPH.

Gearhead Jim

The performance axle should produce a slightly higher top speed, because it lets the engine rev a little closer to its HP peak.
But the difference will be small.

Michael A

Joe is not correct, because he is assuming the horsepower figures at those two RPMs are identical.

Michael

JoesC5

While it is true that the horsepower at 5,175 RPM is slightly less than at 5,520 RPM, it probably isn't more than 10-15 HP. At 190 MPH, 10-15 HP isn't going to hardly change the speed. During that 345 RPM increase, the engine's torque has also dropped some 10-15 lb-ft.

It takes the Z06 some 75 horsepower to increase it's speed from 190 to 198 MPH. It takes the ZR1 some 133 HP to increase it's speed from 198 to 205.

Gearhead Jim

It does take a lot of HP to get higher top speed, but the Z06/ZR1 have a lot of aero changes to improve handling but they also increase drag.

When the base C6 went from 400 to 430 hp, I believe GM said the top speed increased from 185 to 190.

JoesC5

Yep. the 2005 was 186 MPH(that magical 300Kph in Europe) and the 2008 was 190 MPH according to GM's press releases. 4 MPH increase required 30 additional horsepower.

su8pack1

sam90lx

Really in every thread?

steppindown

I do not care about 185 as opposed to 190 or starting the salt corrosion process while on the salt flats at Bonneville.

I was asking the question because the 2.73 rear will provide marginally (and I know that it is marginal) better 0-60 and 1/4mile numbers than the standard 2.56.

Thanks to Bill17601 for actually answering the question asked.

Turbo6TA

I believe buying the C7/Z51 with the A6 trans will be the same as buying a C6 GS with the A6 trans:

The C6 Base / A6 has a 2.56 axle ... The C6 GS / A6 has a 2.73 axle

The C7 Base / A6 has a 2.56 axle ... The C7 Z51 / A6 has a 2.73 axle

In fact, here are the extras that come with the C7 Z51 when ordered with the A6 transmission:

Q7S Split-Spoke Silver Painted Aluminum Wheels, 19” x 8.5” (front), 20” x 10” (rear)
Michelin Pilot Super Sport ZP Tires, P245/ 35ZR-19” (front), P285/ 30ZR-20” (rear)
Brembo Performance Brakes w/ Black Calipers
Performance Suspension
Dry Sump Oil System
Electronic Limited Slip Differential w/ 2.73 Performance Axle Ratio
Differential Oil Cooler
Unique Full-Width Rear Spoiler
___________________________________


.

Turbo6TA

BTW ... That option code GU6 axle (3.42) is supplied with the M7 trans. C7s

I believe both the Base and the Z51 C7s will all get the 3.42 if equipped with the manual trans.

crabman

In fairness however there were at the time quite a number of videos from some of our overseas brothers showing the C6 (LS2) still accelerating when it hit 186 and being limited there. Anyone who has ever taken a car to its top end will tell you that it doesn't just run up there and stop. At the end it picks up the last bit slowly, much slower than C6 was accelerating (although it was not gaining quickily) when it when it hit 186. There is no question it was actually limited at 186 rather than that being its top speed.