Confused about Axle Ratio

[cres171]

I am looking to purchase an R/T Auto trans with 20" wheels. Please clear the confusion for me because I keep getting differant answers. I am under the impression that if you get an R/T auto trans with 18" wheels you get a 3.06 axle ratio. If you get an R/T auto trans with the 20" wheels you get the 3.92 axle ratio. If you get a manual trans with 18" wheels you get a 3.73 axle ratio. If you get a manual trans with 20" wheels you get the 3.92. Is all this correct or am I missing something. Also does posi rear come with the 3.92 ratio on both the auto and manual trans. thanks

[10secDodge]

Auto's only come with 3.06 regardless of your wheel choice. 6 speeds get 3.73's with 18" and 3.92's with 20" wheels. No posi in the auto RT's either.

[cres171]

Thanks for clearing that up 10. No posi kind of sucks[:@] but think I'll stick with the auto trans.

[espo]

I just bought a 2010 RT, automatic. I had the factory install headers and 3" exhaust (magnaflow). When I did a burn out with the esp off, the car left two tire tracks, like a posi. Mine came with the 3:06 rear ratio, I am wondering if a SRT rear differential will fit or from an RT with 6spd transmission. I would do it to get the higher gear ratio. Any advise?

[MaybeChallenger]

factory or dealer installed headers, espo ?

[wp23n]

factory or dealer installed headers, espo ?

probably means dealer installed, my Dad used to do that with all of his new cars back in the 60s.
as soon as it would come off the truck it went in the service dept to have
headers and open exhaust installed.

[espo]

Yes, dealer installed. Headers & exhaust came from a company called SMS. I did it this way so everything is under the factory warrenty. I'd still like to increase my differental ratio, if anyone had done this please let me know.