I just picked up a 97 Trans AM A4, it needed a motor so I built a fresh engine with a little cam to play with. I'm in the process of sending the ECM out to be tuned and the tuners spec sheet asked for my rear end ratio when I found out I have a 2.73 rear end.....

Looking for opinions do I upgrade the gear set to a 3.23, 3.42 or 3.73(I know I have the small carrier and will have to get a gear set from Motive or Richmond) car is nothing more than a cruiser, just don't want the car to fall flat on its face from a roll. I've never had a gear under a 3.23. Or will the convertor work in my favor?

flat top probe forged pistons
230°/230° .480/.480 108 lsa cam
stock heads w LT4 springs
Electric water pump
long tubes
no cats
3400 9.5" PI Vigilante

 

Get the 3.73. You wont be disappointed.

 

3.23 is a great all around gear for the street. 3.73s is a better performance option IMO though. Some people say the gearing is not needed in the auto cars, but it does give you a nice seat of the pants increase. I have run both and I'll be sticking with my 3.73s.

 

I had a 96 TA about 8 years ago that came with a 3.23, it was great all around. After I put the stroker motor in I went with the 3.73 gear set and with the drag radials it was amazing. Street driving on regular radials with the 3.73's and a big convertor was unpleasant.

I've read several posts stating gears are for M6 cars and A4's should go with a convertor similar to mine. Just feel uneasy about having this 2.73 gear, but then again I have never run one with a convertor either.

 

I ran a 383 bout 8 years ago and ran 3.23 as well and this was on a SMALL converter due to "Stall Wall" and a LT4 Hotcam (emission reasons) and to be honest. Even with the Hotcam it was way under stalled and geared. Some people get used to the throttle response and become concerned when there is a "delay" upon inital acceleration. You have to decide what works for you.

As for the M6 vs A4 thing, IMO that is flawed logic. As ALL cars benefit from gearing optimization and launch rpm. The only difference really between the 2 is that Automatics will "slip" vs M6 car will hit and hit hard. The driver and his ability is the main difference between the two.

Due to the difference in 1st gear trans ratio, that is one of the primary reasons you see a difference in gearing recommondation. Also the fact that the T-56 has a 0.50 to 1 6th gear makes it manageable to run a 4.30's all day long street driving.

All cars will benefit from TQ multiplcation, whether it be from gearing, stall speed, or launch RPM based on what the driver does (M6).

IMO I would speak with a converter builder and give him specs on the car and let him recommend. A mis-matched converter, cam, gearing combo is never fun to drive so I suspect that is what you ran into. I think though to spend the money once, go with something better then stock and no 3.42's is a neglible difference. I did it and regretted not going more.

Live and learn.