ACS55

I know our A8 Z06 cars come with a 2.41 rear ratio, and have also read that Z51's came with a 2.73, And I think there may be another ratio being used in between these two.

Has as anyone tried a steeper ratio on the A8 cars? I realize that our 1st gear is so low that with the 2.41 it already equates to a 4.56, at least I have read this somewhere.

But I also know that my car will never see anything north of 150 with me driving it... I bought the car for drag racing... So I don't need the additional top end gearing that would be lost with a steeper gear.

Things to consider..
Do the rear diff's even interchange from non-z06's? Or z06 M7's?
Would the abs freak out? Since the speed sensors in the front would read 13% different from the rear? (Assuming a swap from 2.41 to 2.73)

And lastly, would it improve the ET?

Higgs Boson

you would need to tune for it

you will probably pick up a little bit in the 1/4 but you more than likely will pick up more keeping it from going into 5th at all.

where does your car shift to fifth going down the track? 1000 ft?

ACS55

I'm running 26.0" tall Hoosiers, as opposed to the 26.6" tall stock height rears..
My car is half way through fifth at the trap.

I had had read this before and tried it, but no way to keep my car in 4th, I would redline too early.

Higgs Boson

So you will have to flash the tune to keep it in fourth (raise the shift point and rev limiter in 4th) or you would have to flash it for the new gears so either way, tune required.

JHEBERT

I will say that there is at least 1 c7z running a 2.73 ratio by using the z51 carrier and ring/pinion gears. The 1-2 shift was a bear to tune (even after axle ratio adjusted for). It was an experiment because he broke the spiders in his diff. He now has a custom 4-pinion spider setup

He's a division 7 racer out west

Bob U

It will be fast if you can hook it. Not much difference between 2.41 and 2.73. Don't think there would be much difference in top end eigher as it will only put you more into a better rpm range.
I agree, with a tune to shifting higher, you will get better 1/4 times. I'm will to bet there's a 10th or two by making it shift right at 6600rpm for each gear change and maybe another 10th or two by raising the shift points closer to 7000

ronsc1985

There are several programs available which will predict your drag race performance. Some are really detailed where you put in the engine power vs rpm curve, port size and shape, torque converter operational specs, leave rpm, shift points, gear ratios, track characteristics etc.

I used one for years running a six second drag car. It turned out that the money I spent on the program was paid back many times by not wasting money trying out expensive modifications and when I did make a change the range of performance to expect.

I have no idea what is around now but it should be better then 8 or 9 years ago. An internet search may save you a lot of time and money.

The software I had was from a company called Performance Trends. They are still in business although I don't know what their current offerings are.

383vett

The difference in gear ratios is 13% which is quite significant. Perhaps you are more used to dealing with gear ratios in the 3's. If you started with a 3.73 gear ratio and increased it 13%, you would be running a 4.21 rear end. It may sound more significant but is the same percentage increase.

div7racer

I am the guy who put 2.73s in (along with a 4 pinion spider set up) when the spiders in my 2.41 broke.I used the Quarter Jr drag race program to analyze the difference in 1/4 mile performance before committing to the change, and it indicated about .10 better ET, and about .05 better 60 foot.I will say as long as you can hook up the car in low gear it is just about exactly what i experienced. The overall first gear ratio changes from a 10.48 to a 12.44 with the 2.73. It still goes through the traps at the same MPH in 5th gear, but at close to 6000 RPM instead of around 5000 RPM. Ed

JoesC5

Half of the valve lifters might not agree with upping the shift points beyond the factory setting.

ACS55

Thanks for posting your results, I suspected this might speed the car up, but I was hoping for a larger decrease in the ET (aren't we all?).
So, our C7Z's only come with a 2 pinion spider setup stock?
How did you convert it to a 4 pinion spider? factor parts?
Did this change make it difficult for you to maintain traction off of the line?
I assume you have to tune the ecm for the different rearend ratio?
I assume that if you didn't tune, the abs would freak...
Thanks again for sharing your knowledge on this point, you're the only guy that has performed this change that I am aware of.

div7racer

Yes, both the std and ELSD have virtually the same spider gear set-up, and it is a regular two pinion design.
To convert it (this is an abbreviated summary)I added two 1/2 cross shafts 90* to the existing cross shaft inserted through the case in two new holes,2 more spider gears from a C6 differential, and a connector block on the existing shaft to accept the ends of the two cross shafts.
The modified cross shafts started as a 9" ford differential shaft , I machined the connector myself from a block of 4340 steel,the necessary shims were from 9" ford units, and I also made some small pins to keep the added shafts in place.
I am currently using Hoosier 335-30-18 DOT Drag radials and traction is not an issue.I was able to run 1.60 60 foots on the stock Michelin Pilot Super Sports but the burn outs necessary were wearing them out pretty severely so I changed to the Hoosiers.
Tuning the ECM gave my tuner(s) some difficulty, mostly with getting it to shift from 1-2 w/o hitting the rev limiter when at full throttle.
Not sure about the abs, immediately after swapping gears the ECM was re-programmed for the new ratio,and I drove it cautiously to the shop to have that done.
I have some more of these differentials to convert for others, but am having difficulty getting the replacement parts I need from GM to repair their broken differentials(I need to start with a good working unit)
Ed Urcis

Frank Tamez

Ed

Don't you run Comp?

I ran Div 6 for about 10 years but have run Div 7 in Top Comp and Top Sportsman At Fontana, Vegas, Phoenix and Tucson when they had a Divisional.

Now I play with my Z06 and GT-R and run my mouth

Frank Tamez
6552 TS/Advanced ET

8850

A correctly sized loose torque converter will do much more than changing gears. Can't say for sure with our supercharged cars but I picked up .6 et with my 2008 C6. Of course it would require tuning as well.

If you want to pick up 60' the quick and easy way then a tune to eliminate all the launch torque management with the throttle body. As mentioned previous posts my throttle body was not 100% open until 32 mph. Only 50% at 9 mph.

MIGHTYM0USE

doing this now, what was the surprise?

it should be change the axle ratio under speedo

then change all the shift speed mph's by 89% (2.41/2.73)

what else is there i am wondering. thanks.

onebad1lE

Gear change

Corvetteventeam

Hello Bro I also want to change the rear differential to 2.73. Where did you buy the ring and pinion. Can you please share the information about from who you Porsche the diferencial or the ring and pinion.
thanhs

daniel

thrilled

There’s a company selling 3.90 and 4.10 gears.I have the 4.10.I just have a C7.Don’t know if they have the gears for the Z06?

div7racer

Daniel, I bought a used ,complete differential from a Z51 auto car from a wrecking yard in Fontana .CA, close to the Speedway/Drag strip.It had ELSD and 2.73 gears. I modified it to have a 4 gear carrier instead of just a 2 gear one,
like they come from GM.I wonder if GM is selling the 2.73 gear ratio yet ?

Corvetteventeam

Thanks Bro that is what I’m planning to do I have one identified in eBay. I have a Stingray base model but need better acceleration for roll and drag racing.