TWS Racing

Checking into upgrading the anemic 2.56 factory diff in my 2008 A6 base coupe. Compared a 3.42 diff out of a 2007 M6 coupe, and it has an opening for a smaller T-56 transmission shaft so it won't work. What factory diffs will fit the larger 6L80E transmission shaft? The 2.73 "performance option" diff,I would imagine, but are there any steeper than 2.73 gear option diffs that will mate right up?

If not, where is the best source for a set of steeper gears that will fit in my original diff?

HOXXOH

A 3.42 Z06 dif will fit, but if you're looking for bigger gains, go with a higher stall converter. The 3.42 will give you a max of .1 seconds in the 1/4. Even a real street friendly 3200 stall can double that for about half the price.

TWS Racing

Thanks, but already have a Circle D triple disk 3200 stall.

Guess I need to look for a ZO6 diff, because the 3.42 diff that we compared was for a smaller transmission shaft. If what you say is correct, the one I looked at must have been from a base coupe with manual trans. I don't intend to go to the dealer and plunk down rape money for a brand new one. Idea is to find a nice used unit that checks out.

HOXXOH

If you're serious about racing, the 3200 stall is way too small for a NA motor, but it's fine for street use. Use the forum search function or google regarding the install of a Z06 dif to a 6l80e trans. Been done many times, so shouldn't be too hard to find. You might include subfloor as a search term.

TWS Racing

Thanks. I "know" subfloor and have talked to him in the past. I'll do the search.

That's the thing about asking for advice on forums - and I appreciate yours - the advisors always want to go off on a tangent - sometimes that's all they do rather than just answer the question. At least you answered the question too. But about the tangent: the car is not remaining NA for long. I'm only partway through the build. It's also not going to be a track-only car. It will see street use. At least that's the idea now.