Bigrob339

Hey guys, I am in the process of puttin headers and a LT-4 hot cam with 1.6 roller rocker in my LT-1. I am going to be puttin new rearend gears in and i have heard that 3.42 are best for A4 but then i am wanting to know how about 3.73 for the rearend?Also i am wanting to to be quick, but as be able to run on the highways decently. Right now i have 2.73? I also have hooker exhaust,moroso intake and throttle body coolant bypass. Plus the top end was just rebuilt and the head shaved a lil bit. Let me know, I am leaning toward the 3.42's for the rear.

PatriotTA

If you'd do a search, you'll find all the debates. For the most part, the auto guys go with 3.73s and the manual guys go with 4.10s. This website also has a calculations area, with programs to help you decide these things. You can find that page here. It has all the formulas built in, so you don't need any hand calculations.

https://www.camaroz28.com/services/calcs/

Jay-Roll

What Patriot said is correct. But like you mentioned you still want to drive on the highway without much trouble. It's all based on opinion but several people will tell you both sides. Some will say 3.73's aren't bad at all at highway speeds, others will say the rpms drive them crazy and they can practically watch the fuel gauge drop. I personally went from 2.73's to 3.42's for the same reason as you. Wanted better performance, but still wanted reasonable rpms on the highway. I now want to switch to 3.73's. Not because I'm not happy with the 3.42's, they are a great all around gear. But I just don't drive on the highway as much as I used to and I'd rather have the better performance than worry about the highway mpg once a month(which used to be almost every weekend). In my personal opinion 3.73's are probably the best performance oriented gear for an A4(given good traction). Some will even say 4.10's are perfect for an A4, but those people probably barely ever drive their car vs me, I drive it every day during the summer months. Just decide which your going to use your car for more. But honestly either gear will be a great improvement to your A4.

TCAL95Z

Depends on how much you drive that auto on the freeway.
The hot cam loves 4.10's. Probably even better than a torque converter.
My car ran better times and mph with 4.10's than it did with a 2800 vigilante and 3.23's.

I just put in my Strange 12 bolt with 4.11's and it makes the car drive so much better. the hot cam doesn't come on until about 2500-3000 so a 3.23-3.42 is not enough gear in my opinion.
I put the 4.11's back in because I did the 6 speed conversion