Alright I have a 97 Z28 with A4. I was planning on doing headers next but my buddy talked me into doing gears next, due to I will see a bigger improvement. Car has 3.23 gears in it now and he told me to go with some 3.90's. Where can I find these? I have also heard alot of people going with 3.73's, but my buddy who knows quite abit about cars told me I would be much happier with 3.90's. So where can I find these?

 

No one makes 3.9x gears for our 10-bolt. It's either 3.73 or 4.10.
Anything over 3.73 is way too much for us A4 guys......6 speeds are another story.

 

So I should get some 3.73's? How much of a difference will I feel from going 3.23 to 3.73? Break the tires easily? 3.73's a better choice than doing headers first?

 

Oh yeah....the 3.73s were a HUGE difference. I would go with them first. If I floor it ANYWHERE in first gear, the tires break loose and the car gets sideways

 

Where can I find good 3.73 gears for a good price?

 

The cool thing about the 4L60E is that 3.06 first gear...a 3.42 rear gear will give you more "out of the hole pull" than a Th350 and a 4.10 gear...it depends on what youre plan is for the car...3.42s are plenty for a street car that will see some track time...Drag Radials love the 3.42s, but are over powered by the 3.73s..A track car with ET Streets or slicks would be okay with 3.73s...and might pull a little harder on top end depending on where your power band is...I didnt mention the 10 bolt rear..which will not like ETs or slicks for very long....personally I've been running 3.42s and BFG DRs for 8 years with only 1 rear end rebuild, and that was because my Pro Auburn turned out to be "just an Auburn"...A little tire spin saves $$$$..
--Alan

 

Umm, I dont remember where I heard this, or who makes them, but I swear some company just started making 3.90s for our 10 bolt.

 

I think you would see more of an improvement if you got headers. Providing your getting long tubes. If you have emissions and have to settle for shorties or something than my opinion would be different. You'll get a good 30+rwhp from headers and the complement any other mod you make. Rear gears are a must but I don't think they are yet since you have 3.23's. I went from 2.73's and it made a huge difference. 3.23's are a pretty good gear until you start to really get up there in hp. By then just gaining a 10th in the quarter takes a lot so every mod counts. Your current gears allow you to skimp a little on suspension mods and still let you to retain traction outta the hole. Either way you'll be happy.