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Discussion Starter #1
Hello all. I have searched the threads for information on this topic, but I must be too old or stupid to find out just what I am looking for.


I have a 2013 R/T Classic with the auto transmission. Mods installed are the Scat Pack III set up. It is still a sort of a slug. I want more off-line acceleration.


From what I understand all auto trans cars came with 3:06 rear gears. I would like to go with a 3:73 if at all possible. I've had no luck finding info for that gear set, although I think there were some Challenger models with that gear set installed in them.


Another thing that is confusing to me is what rear end I have. I've seen post that described small axels and larger axels. Which rear end would I have, and is there a 3:73 center section available for it? I would like posi-traction or what ever they call that now days. Sure Grip was the old school term.


I would like to keep the original center section assembly and just install the 3:73, and go back when and if and when I choose.


3:91 rear gears would be considered only if the 3:73 is not available. Back in the day I had a 3:55 set up in an 8/34 rear on the E-Body Challenger I had, and that was my "street gear". Even a 3:55 center section would be great!


Any help / info on what is available / what I have is much appreciated!


Rick
 

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Rick you are in luck. I have the exact same car and went to do virtually the same thing as you about a year ago. I did however go with the 3.91 vs the 3.73. But I will attempt to give you all the information I have and you can feel free to reply back with any questions you may still have.
For comparison purposes, I went with aftermarket ported heads and a cam but i would say that our cars are nearly on par power and configuration wise.

You are correct all auto cars came with 3.06. I have never seen a Challenger come with a 3.73 (however I think some chargers did) but I may be wrong. Info on parts can be found at High Horse Performance (thats who I bought my parts through). They do indeed sell a 3.73 conversion however it is the entire center section and not just the internals. They also sell the 3.91 center section. They sell just the centers or the entire conversion kits which include the srt axles which are much beefier than the rt.

My 2 cents: If you want faster acceleration but not beating on it on the highway the 3.73 is just right. If you want an all out acceleration "stop light to stop light" beast the 3.91 is right. When I swapped to the 3.91 I saw a loss of about 1.5mpg (if thats a concern). Doing 80mph on the highway I am turning 3100 rpms (if thats a concern). Your numbers will be slightly less with the 3.73. No matter which you pick the car will feel like a whole different car. As for the swap itself, I would advocate picking a gear you want and sticking with it rather than swapping back and forth. Everytime you swap you will need the car retuned for the gear ratio (if you have a handheld tuner then you can just change it in there). I dont know of a vendor that sells just the internals, only the complete center section or a kit (if you dig through google though im sure you could find something). Both are rather pricey but I would advocate going with a kit so as to get the srt axles (good for about 600+ torque). If swapping the entire center section, you will need a couple of other parts that you can get from mopar. When going with the 3.73 or 3.91, they are both LSDs or limited slip differentials, this is the more modern term.

Any more questions let me know and I can help you out.
 

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Discussion Starter #3
Thanks a Ton for the info!


The entire center section would be the way I go for sure. I used to swap out the 'punkin' on the 8/34 in around 30 minutes, but I was much younger and had no independent suspension to deal with either! I agree with what you stated on re-tuning etc. Better to leave it in most of the time.


I will google High Horse Performance and see what they need now days for such a piece. I think I have the heavy axels from what I've been reading.....but I will confirm that, and order the heavy axels if need be.


Thanks again for your detailed response, it was JUST what I was looking for! If I have any more questions, I will for sure look you up again!


Thanks again!
Rick
 

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What Gear with Supercharger?

Rick you are in luck. I have the exact same car and went to do virtually the same thing as you about a year ago. I did however go with the 3.91 vs the 3.73. But I will attempt to give you all the information I have and you can feel free to reply back with any questions you may still have.
For comparison purposes, I went with aftermarket ported heads and a cam but i would say that our cars are nearly on par power and configuration wise.

You are correct all auto cars came with 3.06. I have never seen a Challenger come with a 3.73 (however I think some chargers did) but I may be wrong. Info on parts can be found at High Horse Performance (thats who I bought my parts through). They do indeed sell a 3.73 conversion however it is the entire center section and not just the internals. They also sell the 3.91 center section. They sell just the centers or the entire conversion kits which include the srt axles which are much beefier than the rt.

My 2 cents: If you want faster acceleration but not beating on it on the highway the 3.73 is just right. If you want an all out acceleration "stop light to stop light" beast the 3.91 is right. When I swapped to the 3.91 I saw a loss of about 1.5mpg (if thats a concern). Doing 80mph on the highway I am turning 3100 rpms (if thats a concern). Your numbers will be slightly less with the 3.73. No matter which you pick the car will feel like a whole different car. As for the swap itself, I would advocate picking a gear you want and sticking with it rather than swapping back and forth. Everytime you swap you will need the car retuned for the gear ratio (if you have a handheld tuner then you can just change it in there). I dont know of a vendor that sells just the internals, only the complete center section or a kit (if you dig through google though im sure you could find something). Both are rather pricey but I would advocate going with a kit so as to get the srt axles (good for about 600+ torque). If swapping the entire center section, you will need a couple of other parts that you can get from mopar. When going with the 3.73 or 3.91, they are both LSDs or limited slip differentials, this is the more modern term.

Any more questions let me know and I can help you out.
I am looking to do the same thing befor adding a suprecharger. I need to change my open rear end to a limited slip. What gear would you reccomend for a supercharged car? 5.7L R/T with auto and 3.06 gear now.
 

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Depends on what you are doing with the car and your preferences. Street car only or track only? Street with a little track time? If you don't care about gas mileage and want the best acceleration possible the 3.91 is best. However with a supercharger, unless you have or plan on getting some very meaty tires, you will be spinning off the line, at the track or on the street. 3.73 is a little lower and more reasonable for the street and a good compromise at the track. Also depends on your track if that's what you will be doing with the car because your gear ratio determines a lot in a quarter mile run. Pros and cons to both. If it were me, I would look more into the 3.73 if I was supercharged but depends on your goals. Any questions let me know.
 

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????? I researched this on another thread since I have a 2014 5A and by end of that thread changing gears in the rear to any other ratio was not a good idea on the autos at all. Something about the way the transmission is, that going to all other combos actually made the car slower and the 3.06 was about as perfect as you could get. Something someone wrote about how 1 through 3rd gear works on the RT auto that other rear end ratios just can't improve on and waste of $$$.
 

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Dragon... if you can find that thread and link it I'd like to see it because that's pure crap. They may be talking about "top speed" with the gear ratios or the final drive ratio but the way you make it sound is that the 3.06 is the only way to go. It definitely isn't. Again it depends on what you want and or are doing with your car. My experience from my swap to a 3.91: my 0-60 dropped from 4.2s to 3.8s...consistently, on street tires, with little spin (not that the on board 0-60 calculator is super accurate). I just took my car out to the track for the first time yesterday (I don't usually race on tracks lol) but I can tell you I smoked one other auto Challenger all night off the line. Talked to the guy in the pits and he had little done to his car but I attribute much of the off the line acceleration to the 3.91. For me right now, I'm not running out of gear in the quarter so the 3.91 is a good fit. You need some accompanying things to go with it. I spin quite a bit and can't stall the car as high as I would like to because of it. I would suggest wider tires to match the gear ratio. But most definitely the 3.06 can be improved upon. Dedicated drag racers would not be switching to different gear ratios if the 3.06 was the be all, end all.
 

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Dragon... if you can find that thread and link it I'd like to see it because that's pure crap. They may be talking about "top speed" with the gear ratios or the final drive ratio but the way you make it sound is that the 3.06 is the only way to go. It definitely isn't. Again it depends on what you want and or are doing with your car. My experience from my swap to a 3.91: my 0-60 dropped from 4.2s to 3.8s...consistently, on street tires, with little spin (not that the on board 0-60 calculator is super accurate). I just took my car out to the track for the first time yesterday (I don't usually race on tracks lol) but I can tell you I smoked one other auto Challenger all night off the line. Talked to the guy in the pits and he had little done to his car but I attribute much of the off the line acceleration to the 3.91. For me right now, I'm not running out of gear in the quarter so the 3.91 is a good fit. You need some accompanying things to go with it. I spin quite a bit and can't stall the car as high as I would like to because of it. I would suggest wider tires to match the gear ratio. But most definitely the 3.06 can be improved upon. Dedicated drag racers would not be switching to different gear ratios if the 3.06 was the be all, end all.
Thanks, found the thread and think post 13 gave me reason to pause. Old guy that misses his Cuda and still trying to figure out these new Challengers! LOL. http://www.challengertalk.com/forums/f180/a5-3-23-s-3-73-3-92-a-555585/


Now on my 2014 RT 5A I got some posts saying it is LSD and some by reading make me think its open rear end…? I did a burn out with traction control off, Sport on and no brake just pedal and did a posi for about 10' then went to single. Then someone posted with traction control on you should be able to do 2 wheel burnout easy?

What car and what have you done to get 4.2 in 0-60 with stock gearing? I'm pretty much stock except Solo cat back x pipe and best is 5.0 and seems thats close being on par with others.
 

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Yeah in that post he's talking about running out of gear in the quarter mile which depends on a number of different factors. What's under the hood, how you hook, etc. Doesn't mean that the car will actually be slower, it won't be but depending on your combination on your car it may not be the most efficient.
The 3.06 IS A LIMITED SLIP DIFFERENTIAL. So yes you can do burnouts easily. If you are talking about your auto not having the 3.06, it does. My window sticker had both the 3.06 and 3.91 getrag listed but all autos have 3.06s.
 

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As for my 0-60, the 4.2 was with ported heads, 270 comp cam, bunch of little internal things, one piece driveshaft, new intake manifold and throttle body.
 

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A 3.73 gear is available in the Challenger, it is the standard equipment for the 6 speed cars without the Super Track Pack. Adding STP brings the 3.91 gear.
I dont believe that all of the 3.06 cars are limited slip. I had a base 2012 R/T A5 that did mostly one wheel burnouts.
 

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Believe the auto's (R/T's) DID NOT have LSD. I know mine didn't, 2010 model. I went with the 3.73 LSD rear gear and axles and you can tell a difference in the seat of the pants and gas mileage. But since then I have went way up in H/P and Torque and had to upgrade the axles again. If you plan on bigger H/P with a SC in the future just buy the 1400hp axles first from DSS and be done with it. Don't be a big dummy like me and buy axles twice and then almost give away the pair you no longer need. Just my 2 cents from experience here.
 

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3.06 was the standard (and only) gear ratio in the 2014 R/T A5 but it was not limited slip. You could order limited slip for $300 extra. Dodge called it Anti-Spin and this swapped the standard 215 mm open rear end for a 226 mm Getrag LSD. This same 3.06 Getrag LSD was also used on SRT A5 from 2009-2014.

The manual transmission cars from 2009-2014 also used this same Getrag rear but gear ratios were different. With 18-inch wheels you got a 3.73, with 20's a 3.92 (really a 3.91 but Dodge called it a 3.92).




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