I have read a lot of threads on here about this and I have narrowed it down to a 3.90 or a 4.10. I have a 2002 formula firebird M6 with 295 35 18 rears and 285 40 18 front tires. catback, larger lid, chris with a/c ram air, slp maf, slp smooth bellow, ported polished throttle body, cold weather throttle crossover delete. I am having speed inc install my gears the gm motive ones with the t/a performance girdle cover.

My concerns are it is a summer toy and I do not drive it daily. I want the better acceleration, but I don't want the cars rear blowing up. I have read the 3.90's are safer, but the 4.10's are noticeably faster. I am also curious if anyone has an idea what the rpms are at at 60 and 80 with each. All the numbers I have heard on rpms are always waaay different. After all the threads I have read I am still torn between these two gear choices. Any help I would appreciate.

 

http://www.f-body.org/gears/ That will give you MPH/RPM info. Honestly, you aren't going to notice any difference between those two choice as far as a "feel" in the cars performance.

 

ok how about the durability then?

 

Either way you are playing russian roulette when it comes to a 10 bolt. I wouldn't worry about which "gear set is stronger". If it's a 10 bolt, it's not a matter of "if it will break", it's "when".

 

After 2 yrs of banging gears with my 4.10s I'm leaning twards the opinion that street tires don't have enough traction to blow up the 10 bolt if it's built correctly. That's just my experience but I'm not delusional about the POS.

 

I've blown 2 10 bolts on street tires. One was my stock 3.42 rear, and the other was a factory 3.23 rear. Both had not been touched from the factory. Both died on street tires, on the street.

 

so many 10 bolt kill stories go for the 4.10s dont worry about durability. if its gunna last then it will. if not AAA only $59 for the first year

 

Ive blown 2 10-bolts. One with 3.73's and only a 2800 stall and bolt ons. And another with 3.42's, a 6.0, 239/247 cam and a 4500 stall at a 50 roll. Actually blew the carrier loose from the housing......aaaaaaaall fucked up.

 

The 4.10s will have you roughly a 100rpm higher then with the 3.90s in the same gear and mph

 

blew my 10 bolt up bought a strange 12 bolt with 4.11s love it. at 70ish im looking around 2000 2100

 

The % of RPM change will be different at every RPM

 

That's why I said roughly.

 

Lol.. well you would have been better off saying "5% change at given RPM"

1000 RPM will have a much smaller change than say, 7000RPM

 

I went with the 4.10s, now I have to wait to get on it until the break in is over to see how it feels. I have to do 10-15 drives of 20-30 min to heat the gear up then let it cool they said. Does that sound right?

 

Go 4.10. I've got 3.90's in my a4 and love it. I rarely drive it but when I do it's a blast. 4.10's would be great in a m6.

 

IMO, 4.10/ 4.11s in an M6 is the perfect gear ratio.

 

omega i just bought a 12 bolt with 4.11s and strange told me break in was 500 miles without getting on it. drive 50 miles let cool down 50 cool down till 500. then change the fluid out and your good to go.

 

They just tell you 500 to be safe. After two heat cycles, change the oil. If it isn't making noise, you are good to go. 500 miles is unnecessarily high.

 

oh ok. mine was making noise from the get go but they told me that was going to happen as well as most of the guys on here.

 

^why take a chance with that much money? i know i wont