Want to change out my DD, 03, A4 gears from 2.73 to 3.15 or 3.42 to make it quicker. Any ideas on costs? Would I notice a big difference with the 3.15 or should I go to the 3.42? Any other things need to be changed (tune, etc.) when changing gears...costs?

 

I put a Yank 3200 convertor and DTE 3.73 gear in my '98. Cost was 2500.00 installed.

 

Give Ricky at Corvettes of Houston a call. He can give you the answers you're looking for and they can also do the work there if you decide.

 

A new differential will run you anywhere from $950 to $1250 plus shipping depending on where you purchase it from and what gear ratio is in it. I believe Fred Beans Chevrolet has the 3.15's at $1050 and the ZO6 3.42's at $1190 but you'd have to check their website to be 100% sure.

When I was shopping this job around South Florida I was quoted anywhere from 2 to 4 hours. Depending on your shop's labor rate that could be as high as $400. You may want to contact a local dealer and see how many hours they quote you on that particular job. All the shops I spoke to wanted extra for the gear oil/friction modifier so it might just be better for you to get some Amsoil or Redline performance gear oil.

You are going to need a tune with either the 3.15's or 3.42's. You WILL hit the limiter at wide open throttle and part throttle shifting will also be affected. You can drop $350 on a Hypertech or Diablo and do it yourself or go with a custom dyno tune for about the same money or a little more. Although they can't do a whole lot more than a handheld tuner for the tranny functions, gear ratio adjustment, and fans they can make a world of difference modifying the air/fuel maps and timing curves. An experienced tuner can get you another 10 to 15 rwhp on a midly modified C5 where as the Hypertech adds a couple of horsepower and the most I've heard with a Diablo is 5 to 10 rwhp.

As far as seat-of-the-pants difference, the 3.15's are very noticeable yet retain 80% of your fuel economy at highway cruising speeds. I too have the 2.73's and am turning 2000 rpm's at 80 mph. My cousin's C5 with 3.15's turned about 2300 rpm's at the same speed. When he switched to 3.42's he was just under 2500 rpm's at 80 mph. His car picked up only a tenth in the quarter-mile with the 3.42's over the 3.15's mainly due to increased wheelspin out of the hole.

In my opinion this job is expensive enough that it should only be done once. Sort of like a cam, go with the biggest you feel comfortable with so as to avoid being disappointed later. You also have to consider future mods such as nitrous or FI when picking your gear ratio. Either ratio is gonna be alot better than the gears you have now and I think you'll be happy with both. They both help eliminate the overdrive "hunting" the C5 tends to do around town because you'll be turning higher rpm's at the same given speed. The custom tune will help alot in this regard also. Hope this helps and let us know what you decide and how you like them.....

 

Are the diffs the same (interchangeable) in A4 and M6 cars?

 

In a word,YES.I have a 3:42 out of a Z06 & I have an a4.

 

yep; except you need to transfer the seal plate from the original A4 carrier to the replacement M6 carrier.

http://mikemercury.home.att.net/342.htm

 

If you're going with an M6 carrier for your 3.42's then the ZO6 is the way to go. Gears are shot-peened for added strength and durability. I think the carrier is too, but not sure on that....

 

Didn't mean to hyjack, but thanks!

 

I changed my A4 2.73 to 3.42 and it was WOW and much more fun to drive. This was for about 5 months before I did my Procharger upgrade. Just those gears alone made the car MUCH more exciting w/ seat of the pants effect and a little tire smoking when she shifted into 2nd. If you don't plan on any further power adders, I'd recommend going to 3.73 for even more fun, but still reasonable out of the hole.

Even w/ the 3.42 rear, my car (pre blower and w/o any other mods except a free flow air intake) didn't squeak a tire off the line unless I power braked a bit off the line. 3.73 should make it perfect.

Lastly, I'd highly recommend going the professional tuner route when u get your gears installed. I did the Predator deal at home and it was a pain as I had to get an update for the programmer which added to my frustration.