The car:
1997 Camaro Z28 M6, 112k mi
Short Stick, K&N FIPK, and possibly a Hooker Catback soon

Trying to decide between 3.73 and 4.10 rear end ratios.

I'm looking for something universal, good for auto-x, daily driving (fuel economy), drag racing, and highway driving (# of RPMS @ 70mph = exhaust volume)

Also, I want them for a 8.5" Series 2 carrier? or Series 3?

What else do I need to know? I'd be having them installed, and already have a quote from someone who's done a rear end swap before. I want to have the rear end fluid replaced, so I'd need to buy some more, and I'll want my spedo recalibrated via PCM quickly therafter (either do it a week before a tuner is in town or have a PCM4Less/MadZ28 PCM ready to go.

 

I'm going to have to vote 4.10, seeing as ~99% of all M6 drivers go with 4.10's if they upgrade gears, same as ~99% of all A4 drivers go with 3.73's. There are a few exceptions to the rule (I ran 4.10's w/A4 ) but law of average says 4.10's are going to be best suited for your M6 .

Mileage? Well, on the highway, it may drop slightly ... ~1 or 2 mpg maybe? But your cruise RPM's are only going to go up about ~300 - 400 RPM in 6th gear @ 70. Not bad.

For drag racing, with the mods you're listing, the 4.10's will leave you with plenty of gear left at the end of the 1/4, crossing the line in 4th gear.

For street driving and even auto-x'ing, you'll always have a "right" gear to grab (they'll be shorter, but more responsive).

You are looking for 3-series gears for a 7.625" (7-5/8") 10-bolt though ... not 8.5" (unless you've done a conversion??? ..... doubtful) .

 

Less traction?

And nah I doubt it.


Why do you have 3.23s ATM?

 

Currently got 3.23's because I had 4.10's in the 3.23 housing, behind the A4, then busted 2 teeth off the pinion, so the 3.23's went back in, then ~2 weeks later and the A4 committed suicide , so then in went the T56!! I've got a set of 3.90's at home waiting to go in . I'll give a report on them in the spring!!!

 

Whoops! hehe.

 

With your mods, I'd say keep the 3.42s IMHO. You probably trap less than 105mph in the 1/4mi. Get a set of 27" tall drag radials for the strip and go through the traps in 3rd gear (which should be around 5800rpm for a 105mph trap speed). That way, you have the same streetability and no loss of gas mileage. The 3.42 is a pretty good overall ratio, and I think 4.10s are just way too much gear for a bolt-on car. Oh yeah, the ring gear size on the 3rd-4th Gen 10 bolt is 7.625".

 

Oops, that's what I meant!! (I did put 7-5/8" in brackets!) ... correction made!! ^ ^ ^

 

I think I'm going 3.73.... Not till spring though. I think 4.10s might be to much for me right now.


I think the rear end has a slight whine so that's why I'm doing gears first, or else I would do LTs.

 

3.42 to 3.73 isn't much of an upgrade, considering the cost involved.

 

I've found the cam to be the driving issue for gears. My HotCam really like the 3.73. I found the 4.10 to be too low for anything other than drag strip blasts. The 3.73 makes good use of 6th and with the HotCam it enjoyed the lower ratio off the line.

After I went to a P1SC and milder cam, I went back to the 3.42 because the 3.73 was too low, as I was leaving stoplights in 2nd about 90% of the time. The cam defines the gears. Unless of course you only want braggin rights at the drags, then you might want a 4.10 cuz it'll shave another tenth or two for ya.