Gear Change for 37's on my 392

Outrun

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I vote 4.88. That way you don't lose the performance vs having the Hemi just make up the difference.
 

pnut

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I vote 4.88. That way you don't lose the performance vs having the Hemi just make up the difference.
x2. I had even higher numerical than this on my JK with 5.7 with 35's and it was so nice to have all that maximum oomph
 

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What will you be using it for the most. Slow crawling the 4:88s will be nice. Plus if you decide to go 40"s in the future that will be that much better.

Sam
 

asuperheat

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Are you unhappy with the performance of the 392 with 37's? I would think it has enough TQ to only have a small affect on over all performance.

I wonder how much the stock axles can take, 470 ft lbs from the motor 4.71 1st gear and 4.88 rear axle will be a lot for those stock 44's to take. I think that will take you out of the max rating even putting it through front and rear axles.

470 x 4.71= 2213 out
2213 x 4.88 = 10802 out
10802 /2 axles = 5401 ft lbs through each axle or 2700 through each axle shaft in a perfect world.

Any one know what the max tq M220 is rated for?

Only thing I could find was a Dana 44 rated for 3,460 ft lbs. nothing on the newer M220
 
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Outrun

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Are you unhappy with the performance of the 392 with 37's? I would think it has enough TQ to only have a small affect on over all performance.

I wonder how much the stock axles can take, 470 ft lbs from the motor 4.71 1st gear and 4.88 rear axle will be a lot for those stock 44's to take. I think that will take you out of the max rating even putting it through front and rear axles.

470 x 4.71= 2213 out
2213 x 4.88 = 10802 out
10802 /2 axles = 5401 ft lbs through each axle or 2700 through each axle shaft in a perfect world.

Any one know what the max tq M220 is rated for?

Only thing I could find was a Dana 44 rated for 3,460 ft lbs. nothing on the newer M220
I read somewhere the axles are stronger than the earlier gen Dana 60s.
I do wonder just how strong they can be built. Chromo shafts, treated gears, gussets, etc. It would be nice if they could hold up after being built. Strong, lightweight, and good clearance.
 
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MrJonnycat

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Thanks for your input…… I decided to go with 4.56s. I would love to go to 40 someday but I wouldn’t trust the axles to handle that. 37’s are the limit for me, I just wanted to restore the correct ratio that came in it stock with 33’s.
 

SSWIM

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Thanks for your input…… I decided to go with 4.56s. I would love to go to 40 someday but I wouldn’t trust the axles to handle that. 37’s are the limit for me, I just wanted to restore the correct ratio that came in it stock with 33’s.
4:56s are definitely the right choice then.

Sam
 

asuperheat

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I read somewhere the axles are stronger than the earlier gen Dana 60s.
I do wonder just how strong they can be built. Chromo shafts, treated gears, gussets, etc. It would be nice if they could hold up after being built. Strong, lightweight, and good clearance.
If that's true I think the dana 60's were around 5,500 so that could work. I'm thinking maybe the ring gear? Don't the M220 use the same spline count as the JK Rubi 32 spline? Maybe they changed the axle shaft material? I hope so it is one of the bigger things I worry about on the 392. My JK has a dana 60 that runs 35 spline shafts because I had issues keeping the dana 44 happy in it with 37's. twisted splines and locker failure but it does have a 4:1 transfer case in it and I have pushed it at times.
 

asuperheat

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Thanks for your input…… I decided to go with 4.56s. I would love to go to 40 someday but I wouldn’t trust the axles to handle that. 37’s are the limit for me, I just wanted to restore the correct ratio that came in it stock with 33’s.
If your going to do the gear swap get some 0-60 times with the 3.73 and the 4.56 and let us know how much it changes the times. Inquiring minds want to know!
 

nowandthen

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Thanks for your input…… I decided to go with 4.56s. I would love to go to 40 someday but I wouldn’t trust the axles to handle that. 37’s are the limit for me, I just wanted to restore the correct ratio that came in it stock with 33’s.
I think you made a wise choice. Stock 3.73 to 4.56 is a big enough jump. I was told to go with 5.13's (from 4.10's) on my 6 speed JK with 37's. That proved to be too much. RPMs burned up a couple sets of gears before I retreated to 4.88's. I think I could have gone with 4.56's and still been happy.
You have an 8 speed trany and an incredibly powerful v8. Good choice on the 4.56's!
 

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