[Riggpigg]

2020 WB Hellcat Challenger, M6. I am tossing around swapping the 3.70 to the 3.90. My question is w/respect to Speedo. Will the Computer need to be flashed to show correct MPH? Or, is it a mechanical instrument, or does it correct itself by wheel speed? Thanks

 

[Octanewide]

Speed sensors are on the front wheels so no recalibration needed for a gear swap.

Sent from my SM-G781V using Tapatalk

 

[2ndAmend]

Plug and play. Just be careful not to damage the boots and seals.

 

[16GoManGoHC]

Made the swap to a 3.90 as well, plug and play, only thing that changes is less mph per gear but better acceleration per gear.

 

[2ndAmend]

Made the swap to a 3.90 as well, plug and play, only thing that changes is less mph per gear but better acceleration per gear.

Hey GMG, I thought you kept the 3.70 but just changed the 1st gear?

I'm not sold on the better acceleration, I’m thinking there might be something to holding the lower gears longer. I'm putting the 3.70 back in before I go to land speed trials this summer. I think I might get a better speed in the 1mi because I'll be able to hold 5th longer, we'll see.

The 3.90 is much more pleasant to drive around town, but there is a noticeable drop in highway mpg.

 

[16GoManGoHC]

Hey GMG, I thought you kept the 3.70 but just changed the 1st gear?

I'm not sold on the better acceleration, I’m thinking there might be something to holding the lower gears longer. I'm putting the 3.70 back in before I go to land speed trials this summer. I think I might get a better speed in the 1mi because I'll be able to hold 5th longer, we'll see.

The 3.90 is much more pleasant to drive around town, but there is a noticeable drop in highway mpg.

I changed from a 2.98, 2.10, 1.43 1-2-3 ratio trans to a 2.66 1.98 1.40 1-2-3 trans and wanted to get a deeper third gear back so I went with a 3.90 unit. I still have my original 3.70 and a brand new in a box one as well if I want to go back to 3.70 ratio someday. That someday may never come as thinking of selling my cat as well possibly as I’m tired of the BS I work in of late and thinking of liquidating everything I own house tools mill lathe welders everything including the kitchen sink and moving out by my kids and starting over in a semi retired state. Starting with these Diffs.

 

[Riggpigg]

I changed from a 2.98, 2.10, 1.43 1-2-3 ratio trans to a 2.66 1.98 1.40 1-2-3 trans and wanted to get a deeper third gear back so I went with a 3.90 unit. I still have my original 3.70 and a brand new in a box one as well if I want to go back to 3.70 ratio someday. That someday may never come as thinking of selling my cat as well possibly as I’m tired of the BS I work in of late and thinking of liquidating everything I own house tools mill lathe welders everything including the kitchen sink and moving out by my kids and starting over in a semi retired state. Starting with these Diffs.

That's really what Im after is drivability, the car is too tall for my liking, coupled with the throttle by wire and the 370, taking off from a complete stop feels awkward, the pedal commander didnt seem to help either. I think the 3.90 would be a welcomed change. Do you have a 3.90 unit for sale? Or did I not understand what you're stating?

 

[2ndAmend]

Ya, that throttle by wire is a PITA! You are the only other person I have heard say that! I did the same with the Pedal Commander, that lasted 1 day.

If GMG doesn't have one, look at all the mopardiscountplacesoutthere.coms. These are dealers that sell at internet discount out of their parts dept. Walk-ups pay retail why internet buyers get the big discount.

 

[16GoManGoHC]

That's really what Im after is drivability, the car is too tall for my liking, coupled with the throttle by wire and the 370, taking off from a complete stop feels awkward, the pedal commander didnt seem to help either. I think the 3.90 would be a welcomed change. Do you have a 3.90 unit for sale? Or did I not understand what you're stating?

Sorry I thought this was a for sale ad I just put up for 3 370 Diffs for sale, no I don’t have a 390 for sale sorry

 

[Mean Cat]

I changed from a 2.98, 2.10, 1.43 1-2-3 ratio trans to a 2.66 1.98 1.40 1-2-3 trans and wanted to get a deeper third gear back so I went with a 3.90 unit. I still have my original 3.70 and a brand new in a box one as well if I want to go back to 3.70 ratio someday. That someday may never come as thinking of selling my cat as well possibly as I’m tired of the BS I work in of late and thinking of liquidating everything I own house tools mill lathe welders everything including the kitchen sink and moving out by my kids and starting over in a semi retired state. Starting with these Diffs.

Dang Mike can't believe you are thinking of sell the cat, but I know things can change, good luck with your decision.

 

[Frosty]

The 3.90 is much more pleasant to drive around town, but there is a noticeable drop in highway mpg.

How much worse? I obviously didn't buy the car fir it's MPG but I'd be lying if I didn't say the highway MPG has been a very pleasant surprise. My HC is my most comfortable car so it's becoming not only my play toy but the car I've been choosing when I'm taking a longer distance drive.

This is something I've been considering along with the direct connection stage 1 kit. Thought about trying to grab one when I got that kit too.

 

[Frosty]

Sorry I thought this was a for sale ad I just put up for 3 370 Diffs for sale, no I don’t have a 390 for sale sorry

Swap in a 3.70 before you sell your car and sell me the 3.90 at a discount. I can dream can't it

But don't sell your car! Who would I bug then to help me with my car issues? I know the feeling though. I've considered selling off my collection to and retiring early.

 

[Jonx96]

I changed from a 2.98, 2.10, 1.43 1-2-3 ratio trans to a 2.66 1.98 1.40 1-2-3 trans and wanted to get a deeper third gear back so I went with a 3.90 unit. I still have my original 3.70 and a brand new in a box one as well if I want to go back to 3.70 ratio someday. That someday may never come as thinking of selling my cat as well possibly as I’m tired of the BS I work in of late and thinking of liquidating everything I own house tools mill lathe welders everything including the kitchen sink and moving out by my kids and starting over in a semi retired state. Starting with these Diffs.

Man. I would hate to see you tell your cat. Be a lot of knowledge leaving the community if that happened. But you have to do what’s best for you. Just don’t follow your sons footsteps and go import 😊

 

[16GoManGoHC]

Man. I would hate to see you tell your cat. Be a lot of knowledge leaving the community if that happened. But you have to do what’s best for you. Just don’t follow your sons footsteps and go import 😊

I LOVE my cat, will be a very hard decision, we’ll see how the work front and my patience goes these next few weeks, with any luck my new boss will meet a calamity of some sort as he driving the place into the ground. Can’t get workers now but he thinks different, and I’m not doing it all when my team calls it quits.

Covid for Christmas was good for one thing at least got the kids 8 straight and it’s on the road. I never thought I’d complain about too much boost but the turbo kit we put on the car even with waste gate tied wide open was hitting 18 psi of boost at 5500 rpm and redline is 9000 (rotary engine) even with waste gate tie wired wide open and a block off plate in the Auxiliary Power Valve ports boost was out of control, no way the stock engine would take that for long but I tell ya someday we’re going to have to build an engine that will as when the APV opened at 6000 rpm it was like a shot of nitrous hitting. That little 1.3 liter rotary broke the tires loose in third at 55 mph, damn was that fun!! Even with the waste gate hogged out as big as I could take its still hitting 15 psi at 7500 rpm in -2500 DA so we had to cap the APV and rpm limit it to 7200 until warm weather comes round. Boys happy with it, he’s been wanting to turbo a 8 for years. Next he’ll be bugging me to build a beefed up engine and uncork that APV and add a different spring to the WG actuator, he needs to get used to this new power level first. His smile was PRICELESS!!

 

[2ndAmend]

... That someday may never come as thinking of selling my cat as well possibly ...

If you sell the cat, your kids may never experience driving a manual ICE..

 

[16GoManGoHC]

He knows what it’s like

 

[Riggpigg]

OK, update here, got the 3.90 Diff in, I like it a lot!!! Easier starts from dead stop, feels like a real car now lol....in 4th its 66 mph at around 3000 Rpm, the 370 was around 70, It doesn't sound like much, but it has made this car much more drivable in my opinion....I set the Pedal Commander on sport w/lowest setting. Im happy...Carry on...

 

[Frosty]

Thanks for the update. I'm looking at doing this at the same time I do the direct connection stage 1 kit. Think 750+ with a 3.90 will really make this car even more fun without being to crazy.

 

[2ndAmend]

Thanks for the update. I'm looking at doing this at the same time I do the direct connection stage 1 kit. Think 750+ with a 3.90 will really make this car even more fun without being to crazy.

I have the 3.90, and it certainly makes the car more driveable around town, if you just do normal driving, it is the best choice. But as far as performance, in my opinion the jury is still out. In the ¼, I’m not sure there is an advantage, and in the 1-mile, it is my belief that the 3.70 is better because I think holding the lower gears longer might result in a higher speed. With the 3.90, the car roared in 5th right to redline but when I hit 6th, it was a dog. I plan to put the 3.70 back in for speed trials next summer to test the theory, stay tuned!

 

[Frosty]

I don't race this car so not worried about 1/4 or trap speeds. This is more my fun around town car. Just looking to maximize the cars fun factor without going crazy and needing fuel mods or aftermarket tunes (thus the interest in only the direct connection kit).