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Old February 26th, 2012, 02:24 AM   #1
joescamaro67
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Default Atlas ratio question

So after breaking the output on my 231 transfercase Ive been thinking of buying a atlas. But not sure as to what ratio is best. For the most part i like my stock ratio because i always wheel in 4lo, seems to have plenty of low end grunt in the low gears (1-2) and lots of wheel speed on the higher gears(3-4).
As soon as i thought about buying a tcase I was thinking 4.3-1 But now im thinking 3.8-1. I think my stock ratio is 2.7-1 And ive played with axle ratios enough to know theres a big diffrence between 2.7-1 and a 4.3-1 but is there that big of diffrence between a 4.3 and a 3.8.
So what ratio do you guys think would be best and why?????
Its a tj with a 5.3 ls 5 speed ax-15 dana 60`s and a 5.38 ratio on 40`s



And advanced adapters is saying I cant fit one in my jeep without a bodylift. Anybody running one in a tj with no bodylift?
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Old February 26th, 2012, 07:40 AM   #2
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I would go 3.0 or 3.8. Because of your 5.3, probably 3.8.
I'm running a 6.0/TH350/3.8 & 4.88's with 40's. I've never felt like I need a lower gear. More HP at times yes, but not a lower gear. If you feel like you have all the umph you want for bumping on rocks & logs, the next thing you want is to be able to generate wheel speed immediately. A lower gear generates RPM, but not wheel speed.

Yes, your NP231 is 2.71:1. When I had my NP231, 2nd gear low range was my strong gear. Now with the 3.8, my strong gear has moved to 3rd gear low range. It's great because all I do is shift it into D and let the trans do all the thinking. Before, I had to intentionally pull it down into 2nd.

Mine is in a YJ with a body lift so I can't comment on the fit. But Tab has an Atlas in a TJ and I don't think he had to do anything special.
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Old February 26th, 2012, 07:52 AM   #3
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i have the 4.3 in mine,but i am running the 4.0. sometimes it is a little bit too low for trail riding but in the rocks i love it. I suggest getting the 4 speed you can get your stock ratio then have the lower gear when needed. I have a yj with no body lift and a little bit of custom hammering to the floor boards was needed,but i have my skid up pretty high. Kenny has the 4 speed in his tj with a 1in body lift and it fit nicely
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Old February 26th, 2012, 08:20 AM   #4
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Hmm now this has me thinking. I'll be putting an Atlas in with my LQ4 and was going to order the 4.3. I'm currently running the 4.0 and 4:1 gears in a D300 and loved it. I'm guessing with more hp and overall power in the motor the 3.8 would be better? I don't think I'd want to go down to the 3.0. Now the question would be if going with 3.8 do you spend the extra money on the competition grade if you aren't racing KOH style?
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Old February 26th, 2012, 08:38 AM   #5
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I'm running a 5.3, 700r4, atlas 3.8,and 538 gears in my yj. I love it. I switch my from High to low depending on what I'm doing.

Last edited by little_yj_95; February 26th, 2012 at 08:41 AM.
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Old February 26th, 2012, 09:20 AM   #6
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I have the 3.8 with 5.13 gears and 40's but the super sweet 4 liter. For me its perfect.....if/when I go to a real motor it may be a bit too low but your only other option is to get the 3.0 or a 4sp. I don't like the 4sp since none of the ratios are that great. Your low will be way too low like a 5.xx or 10.xx. I think you'd be happy with the 3.8 but for some of the higher wheelspeed stuff you find yourself in 3rd or 4th gear, if you can manually select it.

I happen to have a 1.25 body lift on mine and a one inch motor mount lift so I can't help much there. I will say mine is almost flat and I have a flat skid that only hangs down an inch or so. And thats mostly because I wanted the skid to be independant of the tranny/t-case crossmemeber.
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Old February 26th, 2012, 09:22 AM   #7
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Quote:
Originally Posted by tw1st3d5 View Post
Hmm now this has me thinking. I'll be putting an Atlas in with my LQ4 and was going to order the 4.3. I'm currently running the 4.0 and 4:1 gears in a D300 and loved it. I'm guessing with more hp and overall power in the motor the 3.8 would be better? I don't think I'd want to go down to the 3.0. Now the question would be if going with 3.8 do you spend the extra money on the competition grade if you aren't racing KOH style?
You won't need the comp one. There are thousands of these out there with no issues running strong. The comp came out when guys were running them at speeds of over 100mph and due to their gear design would get way to hot and parts would fail.
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Old February 26th, 2012, 09:26 AM   #8
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You won't need the comp one. There are thousands of these out there with no issues running strong. The comp came out when guys were running them at speeds of over 100mph and due to their gear design would get way to hot and parts would fail.
What I was thinking but it never hurts to get other opinions. Are you running the standard duty output or the HD one? Any opinions on that?

Sorry to hijack your thread Joe. It was just good timing and I was going to post a thread about this shortly.
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Old February 26th, 2012, 09:40 AM   #9
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Get the 31 spline outputs.
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Old February 26th, 2012, 09:44 AM   #10
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Rear is already HD but you pick your yokes. I run a 1310cv since I already had my regular and spare rear driveshafts made and they fit with the Atlas swap. Plus I only run a stock 4.0. I upgraded the front since it's only an extra $150 or so to do it when you order it rather than later. If you do it later it's much more expensive and I think you have to ship it back to them to do it. I run a 1350 front. Plus to go to a bigger rear yoke its as easy as putting a bigger one on.
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Old February 26th, 2012, 09:44 AM   #11
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Quote:
Originally Posted by tw1st3d5 View Post
What I was thinking but it never hurts to get other opinions. Are you running the standard duty output or the HD one? Any opinions on that?

Sorry to hijack your thread Joe. It was just good timing and I was going to post a thread about this shortly.
Highjack away man There all good questions. I was wondering the same but didnt want to sound like a idiot on the first post.
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Old February 26th, 2012, 09:49 AM   #12
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Get the 31 spline outputs.
My 1350 cv flanges are 32 spline. whats the advantage or disadvantage of a 31 spline? I am curently running a 1350 rear and a 1310 front and was going to order the cast that way until i break the front driveshaft then i have a extra new flange to switch the front to 1350. As long as i can reuse my front shaft.So that leads to another question,Will I need new or reworked driveshafts with a atlas???????????????????????
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Old February 26th, 2012, 09:54 AM   #13
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The stock front is 26 spline and upgrade to 32 spline. The rear is standard 32 spline but they offer an HD version which upgrades the output shaft to 300M material. It's about a $250 upgrade though.

I'll be keeping toy flanges for now I think since that's what I'm already running.
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Old February 26th, 2012, 09:54 AM   #14
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with an ax15 id go for the 3.8 ratio. if you had a creeper 4 spd like i do i would lean towards the 3.0 highlander. my gearing is kinda low for much of michigan. 6.32 creeper 1st and 4 to 1 low, is only needed in the big stuff. probably great out west in dry rocks though. i run high range and creeper 1st alot, unless im in something pretty challenging. there is always mud on the rocks i run, and my tires, and my wheel speed is limited in low/low.
looks like you run rocks mostly so the ax15 with the 3.8 would fit you well. im sure your ax15 shifts better than my t18, so you have more gear options.
in sand and mud the highlander would be great.

Last edited by joe_jeep; February 26th, 2012 at 09:57 AM.
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Old February 26th, 2012, 09:54 AM   #15
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I think they are 32 spline. The front you should really upgrade now, like I said, it's a lot more expensive later and not as easy as just swapping yokes like the rear. When you call and order it they will go over EVERYTHING with you. Awesome customer service!

On mine with an aw4 and a 231 I was able to keep the rear (it was within a 1/2 inch) and I had to shorten the front almost 3 inches. No biggie sine my front shaft is really long and flat with the high pinion front. I shortened it myself by gringing out the weld, cutting the tube, and re-welding it.
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Old February 26th, 2012, 10:03 AM   #16
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My bad on the spline count. Either way, like Tab said, do it now rather than later. I'm running 1350's all around.
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Old February 26th, 2012, 10:15 AM   #17
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3.0 or 3.8. depends what you do more. slow crawling or higher speed climbing. i had a 6.0 4l65 5.13s with stock dana 300 gears and felt it was real good for everything. now i have a 6.0 again with a 350 trans and 5.38 gears. when the funds reestablish themselves after my build i'll either upgrade my 300 outputs or pony up for the 3.0 atlas.
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Old February 26th, 2012, 10:24 AM   #18
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Quote:
depends what you do more. slow crawling or higher speed climbing.
I guess I was hopping for a "best of both" ratio but obviously theres not
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Old February 26th, 2012, 10:27 AM   #19
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Quote:
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I guess I was hopping for a "best of both" ratio but obviously theres not
But with the V8 you can use a low gear and high range.
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Old February 26th, 2012, 10:36 AM   #20
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When I orderd my atlas last year they told me they are all 32 spline fronts now when I asked about the upgrade.
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