I just checked the gears in my (motorless) '97 z28 and found out it really does have 4.10 gears. However, my Firebird has 3.42 gears so I, of course, plan to swap 'em. I hear the obvious statements that 4.10s are much quicker through the 1/4 mile but have a lower top speed and worse fuel economy. But I want to hear your experience with them with good detail.

 

Overdrive pretty much offsets the incorrect assumptions you are making about top speed and mileage.
With the 6 speed in particular 4.10s are very nice.

 

If you've got a stock rearend you better have the minimum support to hold power at the track or you're going to pop it real quick (and ideally, those changes are bandaid fixes). 3.42's have an advantage of thicker teeth than 4.10's in a 7.5" rear.

4.10's are great gears for a 6-speed, but I'd be hesitant to put them in a car that is seeing slicks and track times with an otherwise stock rearend setup. Not to say it hasn't been done, but it's inviting problems in your near future.

 

from a "gearing" standpoint the 94-97 T56 with 4:10 is a great combo. On the street it's a 4 speed. I don't shift into 6th unless going OVER 65mph. At 80mph I tach about 19xxrpm with a 27" tire.

I run a 26" MT ET Street at the track

 

Not necessarily true. The engine must have the power band support that kind of gear ratio.

 

I lost about 2 MPH in the 1/4 with 4.10s but the car is "faster". I still get 24 MPG with 4.10s, that's not an issue.

 

I'm torn on wether to put 4.10's in my 95 T/A in my sig. It has 3.42 right now

 

I picked up quite a bit in the 1/4 going from 3.42 to 4.10 and loved how easy it was to drive in traffic. They are much weaker though. I broke 2 4.10s and the car never saw anything stickier than Nitto 555R drag radials. Snapped teeth right off. It's been a while, but if I recall, I was also crossing the line at 108 MPH which put me over 6000 RPMs in 4th. (I shifted at 6200).

 

Go for it if you aren't going to put sticky tires on the back. For my stock '95 Formula and my H/C/I '97 SS, I have not seen more than a couple MPG's difference going to the 4.10's and that has only been on the highway. My everyday mpg's has actually improved slightly with the 4.10's. Since that is most of my driving.....that is a plus.

The cars are both so much more pleasant to drive with the 4.10's. The double overdrive makes them perfectly useable...unlike 4 series gears in an older/non-overdriven car.

I have broken one set of 7.5" - 4.10's in the SS with street tries, but they lasted about ten thousand hard driven miles....and they were loud when I got the car so I suspect they were not set up correctly to begin with. That car now has a 12 bolt still with 4.10's.

Either keep your 3.42's in case you need to swap back for any reason.....or sell them to someone with an A4 car. They are great with the 4L60E especially if someone has the 2.73's originally.