Worth doing? Does highway gas mileage go down at all or stay the same in an automatic 4l60E 97z? Anyone who has done the swap please post opinions I want to know how 3.42s are in an auto.

 

3.23's to 3.42's is to miniscule of a jump to justify spending the money on gears + install costs.... $400-500

Skip to 3.73's or don't do it all. Gas mileage will suffer a bit with 3.73's, yes.

 

You will see about a 5% drop in fuel economy, and a corresponding 5% increase in acceleration.

Most guys with autos that I've seen tend to go with 3.73 gears. You'll see 15% changes in fuel economy and acceleration there.

In the end, it's all about your goals. Are you making a drag car? For best results with a 4L60E, you want to clear the lights at the top of third gear. Figure out what kind of trap speeds you're expecting once you've reached your horsepower and traction goals. Then figure out how high you want to rev your engine, and do the math to find out which gears will do the trick.

 

i went from the 2:73 stock to 3:73 and it was a huge difference(until the pinion gear shattered). (bad install-never again)then i didn't want any one installing gears in my car, so i went with a factory 3:42 and i like them better then the 3:73.

I can still smoke the tires off and i think it gains ground quicker. (feels Quicker)

i guess what i'm saying is i like my 3:42's but i'm not sure of how big of a difference it would be but i would say yuo will def. notice it.

 

I also went from 2.73 to 3.73. While they were fun, they certainly weren't practical. Gas mileage, daily driveability, etc.

I stepped down to 3.42 and haven't been happier. Pretty good compromise. If gas prices were still what they were the 5 years ago when I got the car, I might consider the 3.73s again

 

Yes, but you guys are comparing going from 2.73's to 3.42's.. apples and oranges...

3.23 to 3.42 just isn't worth it....

3.73's are most certainly daily driveable.

 

As was said, changing 3.23 to 3.42 not worth it at all. Going to the 3.73 is. The difference between the former is so minimal. The only reason to take that out would be if the posi/carrier failed.
Im going to 3.73's from 2.73's, suppose to be a big hit and FUN. Stall has some factor in it.
I would say just stick with 3.23's for the time, money and difference. When the posi goes out, re-think it all.
If you are drag racing the car a bunch that changes the whole story. A 3.55 gear might be your choice then.
Just my .02.

 

I have actually gone from 3.23s to 3.42s in one of my older thirdgens (was putting in a posi, had the 3.42s so figured why not). It was barely, barely noticeable. I concur that is not worth it if you have 3.23s already and don't have another reason to be removing the posi or something. I've had 3.42s in both of my main thirdgens, and IMO they are the best all around gear for a auto car. But 3.23s are close enough.

I don't know about you but I have traction problems already in my 3.23 geared LT1, so I don't see any need to step up the rear end gearing since I'm not planning on running a sticky tire. With 3.73s that should only get worse...

I would get a tune and a 160* stat if I were you, just did that in mine and it was a nice improvement all around with a similar setup to yours. I'm personally thinking about some LCA relocation brackets and aftermarket LCAs now or something similar to attempt to get a handle on traction.