Need advice...upgrade to 3.15 or 3.42?

[1998C5]

:confused I have a 1998 A4 with some bolt ons. Blackwing intake, B&B Tri-flow and Hytertech tuned. With my 2.73 diff I can't rip a respectable hole shot and though I don't want to race I would like to improve my launch.
I am having trouble finding a used low miles 3.42 but have found several good deals on 3.15s and wonder if upgrading from 2.73 to 3.15 will do much for me.

Thanks,

David

 

[Pac-man]

I have a 99 a4 with the 3:15 rear and it rips hard. I was actually thinking of installing 3:73's and a 3300 stall torque converter. I hear there is a big difference between the 2"73 and 3:15 rear. If I do the swap I'll sell you the 3:15's cheap. There's only 11k on them, if you want them. Currently I'm running Borla stingers with a K&N air intake. I don't want to get into the motor so the gears are the sensible thing for me to do. Most of the time it comes down to who has the heavier foot anyway. I don't know why GM even bothered with the 2:73 REAR anyway, everyone who has it wants the 3:15. Does anyone know if the top speed is any different with the 2:73 rear as opposed to the 3:15. I'm trying to figure out why they even bothered with it. I guess to make money on the opt.? Someone enlighten me. Also, any advice on my planned gear swap with converter would be appreciated. Will I have to have the car reprogrammed? Also, does anyone know if my car would benefit from an LS1 edit with only the Borla's and the intake as mods. Thanks everyone.

 

[Pac-man]

Hey 1998C5, Tell me about the hypertech tuning, is it worth it? I don't know much about it, thanks.

 

[DRTH VTR]

I don't know why GM even bothered with the 2:73 REAR anyway, everyone who has it wants the 3:15.

I would bet that it has to do with keeping the fuel economy within the CAFE limits to avoid the gas guzzler tax.

 

[cavettefan]

Bingo! (Fuel economy averaging.) When I placed my order in December, 2002 (which included an upgrade to a 3.15 differential), there was a 3 month delay before the car was built. The dealer had to get the regional factory representative to intercede to get the order processed. The explanation for the delay was that no slots for 3.15 differentials in the CAFE (Corporate Average Fuel Economy) calculation were available until February, 2003. I tend to believe the explanation as the dealer had other orders processed after I had placed my order for cars that did not have the 3.15 differential upgrade. These non-3.15 orders were built in January, 2003.

As a general rule, the 3.15 is probably a middle step on the path for acceleration. (The 3.42 or 3.73 would represent a more radical effort.) There is a definite improvement in launch as well as 0-60, 0-100 and quarter mi. times over the 2.73 differential (duh, nothing new here). There is also a fuel mileage penalty (approx. 2 mpg) if you are hard on the go pedal. However, if you don't push it, there is really no significant fuel mileage penalty and I like the ease of launch over the 2.73.

 

[devo]

3:42's = 2100 RPM's @ 70MPh

I have them in the garage waiting to buy my TC cant wait!!!!!!!!

 

[1998C5]

Hi Pac-Man,

Thanks for the feedback. Apparently I misread the codes in my C5 thinking I am running a 2.73 only to learn from a mechanic friend of mine that I already have 3.15s. He said in any case if I really want to feel an improvement in the seat of my pants off the line he would have recommended upgrading to a 3.42 or 3.73 so I guess I'll keep my eyes open for one of these diffs.

The Hypertech tuning made a slight improvement out of the hole and a substantial improvement when I drop it from 20mph on up. Don't know about top end as I rarely have the chance to get much above 120mph.

My understanding is that upgrading to either gear ratio will require a speed recalibration.

Let me know what you decide to do on your "99...

David

 

[1998C5]

Hey Pac-Man,

Are you running run flats?

David

 

[Pac-man]

Yes, the car came with run-flats, so I figured I'd wear them out before replacing them. My last C5 I had goodyear ef1's then I bought a set of Pirelli pzero's after that. The pzeros were good but only at temp. Why do you ask?