viperZ06

How much REAL performance dfifference is there in these two rear ends on automatics and what are the pros and cons of each? Looking at a auto 2.73 for possible buy. Also looking at a 3.15.

Mike Mercury

To be totally honest, I wouldn't touch a 2.73 A4 unless you were 100% certain to upgrade it in the near future.

the 2.73 is nicknamed the "Gore Gears". A performance car should never have such a ratio GM has to do this to please the CAFE group (which is a fancy name for the environ-mentalcases ).

But if there is a definite rear axle ratio upgrade in your future, I would consider either one.

Special K

Buy either one. If you get the 2:73 figure on replacing it with a 3:42. The 3:15 may not be worth the price of changing it.

shurite44

I think I would stick with the 3:15 even if you plan to upgrade. Not sure if this still holds true but when I was checking the vendors would not take the 2:73 as a trade in.

DTE Powertrain

We do...

Special K

They'll take it Gary. They want the case.

'06 Quicksilver Z06

Except on the point where it might not be worth it to change the 3.15.

Tthe 3.15 is not widely regarded as being that great of a "performance" ratio either. The advantage of it vs the 2.73 is that the 3.15 will give you improved performance at least until you can change to a real performance ratio like 3.42 or 3.73.

Special K

That's true but I don't think he'll notice much improvment going from a 3:15 to a 3:42. I kinda wish I had done the 3:73 and a TC.

It's comimg. Mary says I need to go back to work first. She says I spend to much money. I told her to get a job. I'm looking. It's getting to damn hot down here anyway.

Vette_Fan

Anyone wanna chime in the difference it makes on gas milage, when going from 2.73 to 3.15 OR 3.42....?

XTrooper

There's a world of difference between the two, but the plain fact is neither one of them is worth a damn and both are "desert gears" which you'll want to replace as soon as possible. I bought my car with the 3.15s and even while making 400+ rwhp, the car felt weak below 4000 rpm. Gears are your friend.

Another thing to consider is that the 2.73 rear has a different carrier so the switch to deeper gears becomes more complicated and expensive if your car is equipped with them. If you have the 3.15s, it's a simple ring and pinion swap using your carrier.

Lastly, if you do a swap, skip the 3.42s, and go right to 3.73s. You'll be glad you did.

Special K

You can get the complete unit installed or just the gears. Find the very best in your area to do the work.

Going to 3:42 I lost about 3 MPG but I'm an aggresive driver. If I kept it at 65 MPH on the highway might due better.

byte_me

In my 97 A4 with 3:15's I can turn 2500 RPM at 85MPH...I can get 25 MPG in her as well...I drove a 2:73 car before I got this one...all I can say was it felt like a station wagon taking off...not a vette...I agree 3:15's are not really a performace gear set...but its better then 2:73's!

Good luck! GM Parts direct has a new Z06 3:42 rear (entire unit) for +\- $900 bucks...at least they did the last time I was there...I believe Fred Bean (Forum Vendor) also has them...

ArmyVette

When I had my 2004 A4 coupe with the stock 2.73 gears and torque converter, I was getting about 23 mpg city and 30.5 mpg highway. When I switched over to the 3.42 gears and 2800 TC, I was getting 18 city and 26.5 highway.

I think I was taking a bigger hit on the city mpg because I spend more time in stop and go traffic and tended to accelerate faster.

C5magic

Couldn't have said it better myself.

'06 Quicksilver Z06

Thats about where I am gas mileage wise.

I would think long and hard before going to 3.73s for this reason. There is also an increase in cruising RPMs on the highway, as well as potential traction issues if considering 3.73s and remaining with runflat tires.

3.42s are about the extent of it if you intend to stick with runflat tires.

Also, a few people here have gone from 3.15 to 3.42 and claim a noticable difference. In fact Mike Mercury's gear swap page shows a change from 3.15 to 3.42.

Special K

Good mornen EB. What you say makes sense and I would have thought the same but a friend of mine, Fuzzy Dice runs a 3:73 and is really happy with it. I will contact him and ask him to put in his .02 He's the reason I now wish I had gone to a 3:73.

Fuzzy Dice

Yes, I run 3:73's in my 93 and have for almost 4 years...I drove it daily until last October...I also have averaged over 120 passes a year at the drag strip for the last 3 years...I have taken three decent length trips as well ranging from 1500 to 2100 miles...

I run right at 2850 rpm cruising at 80 mph...gas mileage is about 25 mpg highway and 18 mpg city...I have gotten 28 mpg on the highway with the cruise set at 72 mph....

I have 110,000+ miles on the car now and have had no problems...btw, I am running a 2400 stall converter and a full race Transgo shift kit also.....good luck

Special K

EB you may still disagree but I'm convinced that's the way I should have gone.

XTrooper

I didn't bother mentioning my city mpg for this same reason. First, I always have the tranny in 3rd and second, I'm always in the throttle. Consequently, my "around town" gas mileage is, in a word, dismal.

shurite44

I was hoping you would post because I could not remember the name of your business. Yes, these are the only guys I know that will take the 2.73 as a trade. I am sure this helps you guys out with some extra business. Why is it you guys are able to swap the 2.73 and no one else can, just curious?