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Discussion Starter #1
after seeing Dodge is changing their Mopar 11 drive ratio from 3.08 to 3.92 to get more performance i started to think it that is something to consider on our 392 automatics?

would it make the 392 impossible to launch?

what would this project cost?

how much would it take off 0-60 and 1/4 mile?

id assume a few mpg worse?

just wondering why i dont hear about this mod ever
 

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It's actually 3.91 based on the ring/pinion ratio. If you have the traction, expect 0.3 seconds improvement in the 1/4-mile and maybe 0.5 seconds better 0-60. It will be very noticeable and much snappier and quicker revving and more responsive. MPG will drop, but you didn't get this car for mileage.

I'm impressed Mopar had the guts to throw in the 3.91 gear set into the 2011 Mopar Charger - a one finger salute to the CAFE standards.

Expect the gear set to cost a few hundred and installation will be a few hundred.
 

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Discussion Starter #3
for $500 it sounds like an easy/quick performance boost...

why arent more people doing it?

id go there before all these other mods which may screw with your warranty...i assume if i put a Dodge 3.91 gear set in my rear i wouldnt hurt any part of my warranty
 

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The gear ratio change intrigues me the most about the Mopar '11.

The only suggestion I would have is to make sure the bell housing will allow it. The guys with SRT 10 trucks have been doing it for years.

I am curious what the revs would be at highway speeds and how much would it effect the top end.

Wil
 

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I changed my 09 SRT8 auto from the 3.06 to the 3.91!!!!!!!!!!
Are you happy with your results? What were your 3.06 vs 3.91 stats?

I swapped my Wife's last Mustang's gears from 3.31 to 4.10 and her city mpg when from 12 to 16 (yup, got better!) and hwy went from 27 to 25. I'm planning on doing the same to the Mustang she has now.

I'm thinking about going to the 3.91(2) gears in my SRT8 auto as well.
 

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I don't know if you can just get the Ring And Pinion for your GETRAG to swap to 3.92

But here is the easy way:
Mopar OEM 3.92 LSD Differential 09 Challenger 5.7L R/T, 6.1L SRT8 6 Speed


Now, your going to have to adjust your tune so the car will shift out of first gear without going into limp mode. And since there are no tuners available yet for the 2011 cars you are kind of tied up. :(

Hopefully soon there will be more parts available for the 392s :)
 

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The gear ratio change intrigues me the most about the Mopar '11.

The only suggestion I would have is to make sure the bell housing will allow it. The guys with SRT 10 trucks have been doing it for years.

I am curious what the revs would be at highway speeds and how much would it effect the top end.

Wil
Revs at highway speed are easy - it's just a direct ratio. Say you are turning 1800 RPM at 60 in 5th with the 3.08 gear set. That will change to 1800 x 3.91/3.08 = 2285 RPM.

Top end won't change appreciably - I doubt top speed (reportedly limited tio 173 in the auto) is RPM limited with the 3.08 gear set anyway.

I'm pretty sure the differential case is the same for all SRT Challengers regardless of auto or manual - it's really just a ring/pinion change. Just make sure a good mechanic does the work who is familiar working on that LSD rear-end.

Your speedo will be off a bunch (reading high) until you can put hands on a Diablo tuner to reset the speedo. Or the Dodge dealer can do it - just tell them you need the same speedo flash file as the Mopar 11 Charger.
 

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Your speedo will be off a bunch (reading high) until you can put hands on a Diablo tuner to reset the speedo. Or the Dodge dealer can do it - just tell them you need the same speedo flash file as the Mopar 11 Charger.
Car will not go any farther than 1st gear. It will shut down into limp mode if there is a different gear ratio than what the tune is written for.
 

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Car will not go any farther than 1st gear. It will shut down into limp mode if there is a different gear ratio than what the tune is written for.
Seriously? The factory flash file will not allow a 3.91 install without going into limp mode? Wow...

I guess you should have the Dodge dealer do the install then. That's assuming the dealer will even reflash an SRT8 392 for a 3.91 gear. The Mopar '11 Charger is an R/T 5.7 Hemi.
 

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are you teasing us?

lets hear about the cost & performance?

was it worth it?
Well you can't just buy the ring & pinnion you have to by the whole center section for a 6 speed. I priced several around 16 to 1800.00 plus labor.

You want believe me when I tell you, my best time here at bristol Tn. was 13.6 after the change I run a best of 12.7. It made an unbelievable difference just driving it. My rpm's went from 2450 at 80 mph to 3050 so if you do a lot of interstate driving you may want to rethink this. I have not drove it enough to check the mileage yet but I will this weekend.
I think the car still needs a conveter to get the best it has to offer and will do one as soon as I can.

I would do it over again, thats how I feel. PS The dealer can"t flash for the gear change You will have to use your tuner!!!!!!!!!

Hope this helps, if you have any more questions just let me know.
 

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Seriously? The factory flash file will not allow a 3.91 install without going into limp mode? Wow...

I guess you should have the Dodge dealer do the install then. That's assuming the dealer will even reflash an SRT8 392 for a 3.91 gear. The Mopar '11 Charger is an R/T 5.7 Hemi.
Yup, the factory tune will freak out. Speed sensors will send data back to the PCM and the PCM will shut the car down to limp mode lol

The dealer might be able to flash with their tool to change the gear ratio - its just a problem finding one that would.

Once their are tuners available for the 392s it will be an easy swap :)
 

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Discussion Starter #17
i could care less about the mileage difference....i dont like hearing $1800+ labor to swap it though

i would definitely have the dodge dealer do the swap
 

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It would be nice if someone would make a gear set for our center section.
Should be, gear set 350.00- labor 250.00!!!!!!!!!
 

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Well I just got back from a 300 mile trip mostly stop and go some rural four lane no faster than 65 mph and averaged 22.7 mpg. Thats with the 391 gear's ( still love it and would do it again in a Heartbeat!!!!!!! )
 

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Anyone try putting a set of the 3.7x track pack gears in an auto yet?
Might have most of the benefit of the 3.92's with a tad less rev on the highway.
 
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