SRT Hellcat Forum banner
  • Hey Everyone! Enter your ride HERE to be a part of this months Ride of the Month Challenge!
1 - 12 of 12 Posts

·
Premium Member
2020 M6 HC
Joined
·
853 Posts
Discussion Starter · #1 ·
I hate to beat dead horses, but I would like to get some clear info from people who have actually done it. I am ready to pull the trigger, almost did it today, but there are so many fragmented and conflicting posts that I hesitated.

Could actual users of 3.90’s in M6’s please let me know:

1. Are you happy?

2. Would you do it again?

3. Tell me the good and bad.

4. What was the P/N of the 3.90 diff you installed?

5. Did you install it yourself?

Please hurry, the good weather has arrived and my car has needs!

Thanks!
 

·
Registered
Challenger SRT Hellcat
Joined
·
1,924 Posts
Following...I believe we’ve got 3.70’s and if that’s the case I don’t think going to 3:90’s is going to make all that much difference. I think a far more expensive tranny rebuild with a few gear ratio swaps will be required for any substantial improvements.
 

·
Registered
Challenger SRT Hellcat
Joined
·
7 Posts
I hate to beat dead horses, but I would like to get some clear info from people who have actually done it. I am ready to pull the trigger, almost did it today, but there are so many fragmented and conflicting posts that I hesitated.

Could actual users of 3.90’s in M6’s please let me know:

1. Are you happy?

2. Would you do it again?

3. Tell me the good and bad.

4. What was the P/N of the 3.90 diff you installed?

5. Did you install it yourself?

Please hurry, the good weather has arrived and my car has needs!

Thanks!
1. I am happy with the 3.90, although not much of a difference.
2. Sure.
3. Not much to tell really, I can say it is a little easier to launch the car on a prepped surface track. No downsides.
4. Cannot remember, did it a few years ago. I believe it the part number comes from the M6 392's.
5. I did install it myself, did the diff brace at the same time.
 

·
Registered
Charger SRT Hellcat
Joined
·
105 Posts
Good swap in my opinion. Made the car a little easier to launch and a bit better driving around town/in traffic. I swapped mine in my garage.
 
  • Like
Reactions: 2ndAmend

·
Registered
Joined
·
2,732 Posts
I run a 2.98 first gear with the 3.73 rear, 3.90 would be too deep for me. If you want to sell your 3.73 to help pay for the 3.90 I’d be interested in purchasing it.
 

·
Registered
Challenger SRT Hellcat
Joined
·
1,393 Posts
i did in my 2015. there isn't much of a difference, like 200rpm? in my mind the car felt better but it's probably not worth it. the CDV delete was a better "mod"
 
  • Like
Reactions: 2ndAmend

·
Premium Member
2020 M6 HC
Joined
·
853 Posts
Discussion Starter · #7 ·
I run a 2.98 first gear with the 3.73 rear, 3.90 would be too deep for me. If you want to sell your 3.73 to help pay for the 3.90 I’d be interested in purchasing it.
I've read about your mods and results, sounds like the best way to go. If it were not an almost new car, I would seriously consider that route. Thanks!
 

·
Registered
Joined
·
565 Posts
Correct me if I'm wrong but wont you also need an unlocked computer to have your speedometer corrected?

Me personally, I would probably go the same route that 16GoManGoHC went and have some gearing changes done in the transmission before swapping the rear gears. Rear is cheaper but not a lot of difference between the stock and 3.90's. I'd really just love a longer 6th gear at .50 OD. I really don't understand why people say 6th gear is useless on these cars as I'm finding that I'm in 6th a lot of the time. At least my car is perfectly happy in 6th gear cruising down the highway or even at 60mph. Our speed limits are 70-75 in most places on the highway so I'd love to drop the RPM a bit when cruising at that speed. That 2.98 first with a .50 6th gear would be awesome for me. A little more acceleration but better cruising RPM on highway.

Here is the ratio in my Viper. I wonder how it would do behind the cat. - 2.66:1, 1.78:1, 1.30:1, 1.00:1, 0.74:1, 0.50:1, :1
 

·
Registered
Challenger SRT 392
Joined
·
7,143 Posts
Correct me if I'm wrong but wont you also need an unlocked computer to have your speedometer corrected?
No, from 2015-up the speedo gets it's signal through the ABS sensors so no correction needed.


Sent from my SM-N960U using Tapatalk
 

·
Premium Member
2020 M6 HC
Joined
·
853 Posts
Discussion Starter · #10 ·
Me personally, I would probably go the same route that 16GoManGoHC went...
Thanks. I have read many of GMG's posts, he is very serious (more than I will ever be) and has had impressive results making him very helpful. I started this thread to explore the (an) alternative that is less expensive and less invasive and hope to hear back from those who have actually tried it and hear their thoughts. :)
 

·
Registered
Challenger SRT Hellcat
Joined
·
815 Posts
1. Are you happy? Yes
2. Would you do it again? Yes
3. Tell me the good and bad. : Dodge Dealership Service Manager said he could install for $500 however would not provide any warranty for the parts or labor and he also said that he would void any and all warranty coverage for my vehicle. That was my last conversation with any Dodge Dealership Service department employee. From that day forward I have done every bit of work and maintenance on my Hellcat myself.
4. What was the P/N of the 3.90 diff you installed? 05038703AG
5. Did you install it yourself? Yes
 
  • Like
Reactions: 2ndAmend

·
Premium Member
2020 M6 HC
Joined
·
853 Posts
Discussion Starter · #12 ·
Thanks for the opinions guys. Especially since it looks like a home shop upgrade. I thought a lot more people actually made this changeover but apparently not. So far the score is: 3 think it is worth it, 1 probably not. I hope to hear more soon in this and other threads, but right now I'm leaning toward dropping the $767 (shipped) for the part. Seems like it is good value and relatively easily reversible. Thanks!
 
1 - 12 of 12 Posts
Top