Topic: Which Atlas Transfer Case

[Jeffy]

So, I've been thinking about this again.  The first thing I should mention is that I want to replace my AX-5 for an NV4500.  I'm thinking Atlas 2 (5:1) or Atlas 4.  Problem is which ratio should I go with.  The easy answer is the lowest available.  That would be 11.70:1.  Although with the NV4500, 8.16 might be a good choice.  That's 2.72:1 and 3.0:1.  The argument being that the ratios basically overlap each other.  With 11.7:1 though you could shift into 2nd and have 182.5:1..  I know a few members have compound low transfer case gears.  Think 11.7 would be two low?  I know Taco guy's stack Marlin crawlers.  I think the lowest I've seen is 580:1 on an employee's rig.  I'm currently only running 33's and don't really have plans on going larger.  The toughest trail I've done so far is the Rubicon and 2.72 just doesn't cut it.  I don't think 4:1 would either with the 2.5L.  Something in the low 100's would be optimal and anything above that is gravy.  So realistically, 5:1 would work.  143:1 (1st)/77:1 (2nd)/43:1  (3rd)

AX-5 x 5 x 5.13 = 101
NV4500 x 5 x 5.13 = 143
AX-5 x 8.16 x 5.13 = 164.9
AX-5 x 10.34 x 5.13 = 208.9
NV4500 x 8.16 x 5.13 = 234.8
AX-5 x 11.7 x 5.13 = 236
NV4500 x 10.34 x 5.13 = 297.6
NV4500 x 11.7 x 5.13 = 336

[95 Lowbuck]

I guess if your main fun will be on the rocks, the Atlas or the oem rocktrac would help.
I think I remember you’re running 4.56’s, I run 4.88’s and 33’s, and your right,
a lot of clutch work on the Rubicon with the stock 2.72 case.
I find with the 4 banger, I typically am the first to shift into low range in my club,
and the 2.72 for the most part does the job.
I debated about getting a 4.1 kit for my 231, but didn’t want to live with it all the time.

[Jeffy]

I guess if your main fun will be on the rocks, the Atlas or the oem rocktrac would help.
I think I remember you’re running 4.56’s, I run 4.88’s and 33’s, and your right,
a lot of clutch work on the Rubicon with the stock 2.72 case.
I find with the 4 banger, I typically am the first to shift into low range in my club,
and the 2.72 for the most part does the job.
I debated about getting a 4.1 kit for my 231, but didn’t want to live with it all the time.

Currently my axles are 4.56 but I'm planning on 5.13's so it's more driveable on the street.

Looking at the numbers. if you had 4:1 and shifted into 2nd, you'd have 42:1(2.33x4x3.45) vs 49:1(3.92x2.73x4.56).  Really you need to calculate all of the gears (minus OD) to see that the spread is like.

Problem with the Teralow is that it's noise and prone to breaking.  I don't think you can get a RockTrac to bolt up to an AX-5.  I haven't been able to find out if you can swap the input shaft or not.  My assumption is yes, since a lot of NP2xx parts are interchangeable but for the price of a 231OR, I could get a Atlas 2 and have twin stick, a shorter case and gears rather than a chain.  I've had a few times where 2Low has come in handy.

So for me, really it's the Atlas 2 5:1 or the Atlas 4 11.70.  The only downside to the Atlas 4 is the gearing gets really low with compound gearing.  If I keep the 2.5L though that shouldn't really be a problem. Thee downside to the 5.1 is fewer ratios and limiting the top end to 143:1.  Though that's a nice ratio for the Rubicon from what I've heard and have experienced.

I'm also looking into if you can mate a TR4050 to the 2.5L.  That should be a better transmission than the NV4500 as it weighs 40lbs lighter and has a lower 1zt at 6.16:1 and 2nd at 3.11:1.  With a Atlas 5:1, 2nd gear should give me the equivalent of a 4:1 and 3rd would give me what amount to 2.72:1.

[Jeffy]

Well, I talked to SST who with Tremec packaged the TR4050 and they said they didn't have an application for the 2.5L/GM 60* bolt pattern.  Sucks but I wasn't expecting to see one as the GM 60* family gets overlooked for the 90* pattern.  Would have been nice to shed 40# and had a lower 1st.  But that's a lot of money to spend for a nche group.

The downside to the NV4500 is that it's been out of production for more then 10 years but then I don't think it's ever going to be an issue with a 2.5L  It's wat overkill.  Some things to consider is that the conversion on an older YJ adds 1" to the drivetrain length.  IIRC, the Atlas 4 is 2" longer than the 231 but is fine for the front shaft.  An Atlas 2 would give me a longer rear shaft, I'm at 19" now, and shorten the front which isn't an issue.  What I'm wondering though is 11.70 too low to be useful?  1st is a stupid 336:1 in the NV4500 and 2nd is 3.06:1 so that gives you 204:1 and 3rd is 1.67:1 giving you 100:1.  I'm kinda thinking that might be too low to be useful.  If I keep the AX-5 it's a lot more useful though as 1st is 3.92.  Going with a NV4500 basically acts like a doubler.  Going with a 10.34:1 Atlas 4 and 2nd gear would be 162:1 already.  So basically what 1st and a 5:1 would give.

I'm kinda leaning towards the 5:1 at this point.

[FourbangerYJ]

Well personally I loved my 2:46 and 4:1 combo But I think a 2.7 and 4:1 would be perfect!
The 4 speed Atlas should fit the bill just about right. Or a Black Box i and a flipped 300 with 4:1.
Or a 4:3 Atlas then if you feel you need more choices add a Black Box to it. You can do that down the road. Granted you would have driveshaft mods. I sent mine out to be modified vs buying new ones. Much cheaper.
Granted I mostly just ran the 4:1 it did just about everything I wanted with 5:38's on 35's. But I feel the 5:1 would be to low for most trails.

I just tried out my Black Box a couple weeks ago. Im not 140:1 vs 208:1 with the Klune. I do enjoy the 2:7 the 2:46 is not low enough for my tastes.
I ran it in all figurations to see what's what. Having both in low I used 3rd gear on the transmission mostly for the trail I was on. I did use first gear low, low and it was ok. Not near as low as I was before. But it should be plenty for what I do.

Hitting the Dusy next week. I'm sure I will use all the combinations. Where as before I would just use the 4:1. After I switch from 4:88's to 5:38's I pretty much would only use the 4:1 unless it was a very mild part of the trail.

[Jeffy]

Well personally I loved my 2:46 and 4:1 combo But I think a 2.7 and 4:1 would be perfect!
The 4 speed Atlas should fit the bill just about right. Or a Black Box i and a flipped 300 with 4:1.
Or a 4:3 Atlas then if you feel you need more choices add a Black Box to it. You can do that down the road. Granted you would have driveshaft mods. I sent mine out to be modified vs buying new ones. Much cheaper.
Granted I mostly just ran the 4:1 it did just about everything I wanted with 5:38's on 35's. But I feel the 5:1 would be to low for most trails.

I just tried out my Black Box a couple weeks ago. Im not 140:1 vs 208:1 with the Klune. I do enjoy the 2:7 the 2:46 is not low enough for my tastes.
I ran it in all figurations to see what's what. Having both in low I used 3rd gear on the transmission mostly for the trail I was on. I did use first gear low, low and it was ok. Not near as low as I was before. But it should be plenty for what I do.

Hitting the Dusy next week. I'm sure I will use all the combinations. Where as before I would just use the 4:1. After I switch from 4:88's to 5:38's I pretty much would only use the 4:1 unless it was a very mild part of the trail.

So that puts you at 84:1 with just the 4:1.  That seems to be the golden number for the Rubicon.  The TJ Rubicon who was with me was pretty much stock on the same tires and was 65:1 but I know that's not going to be low enough for a 2.5L.  An AX-5 and a 4.3 would already be 86:1.

I'm curious to know how much you use 2nd and 3rd with any combination though...  I just realized you're running 2.46 and 2.72 not 2.46 and 4:1.  That's huge overlap then.  So really you're only using or 2.72 or both.

I'd kinda like to keep it simple so that's why I'm consider a 2-speed over a 4-speed.  I'm sure if I ever do an engine swap 5:1 will be too low...  Gonna have to look at all the numbers again

[FourbangerYJ]

So that puts you at 84:1 with just the 4:1.  That seems to be the golden number for the Rubicon.  The TJ Rubicon who was with me was pretty much stock on the same tires and was 65:1 but I know that's not going to be low enough for a 2.5L.  An AX-5 and a 4.3 would already be 86:1.

I'm curious to know how much you use 2nd and 3rd with any combination though...  I just realized you're running 2.46 and 2.72 not 2.46 and 4:1.  That's huge overlap then.  So really you're only using or 2.72 or both.

I'd kinda like to keep it simple so that's why I'm consider a 2-speed over a 4-speed.  I'm sure if I ever do an engine swap 5:1 will be too low...  Gonna have to look at all the numbers again

I use 2nd and 3rd gear a lot when I had the 4:1.  Now with the 2:7 Im sure I'll be using both boxes in low and rowing between the gears in the transmission up to 3rd gear.

[Jeffy]

So, with an AX-5 and 5.38's a 4:1 would look like this; 84/50/31/21 which is closer to 2.72

Here's the gear spread for a NV4500 with 5.13's which is what I'm planning on running.  I've spaced the ratios out so they kinda line up respectively.  This includes 1:1 in the transfer case which are generally the 3 lowest (numarically) numbers then the 5th. The Rubicon's 4:1 in 4th is the same as 1st in 1:1 so I omitted one.

I threw in your ratios into the chart.  Interesting thing is 3 & 4 in 6.74:1 are actually marginally higher (numarically lower) then 2.72:1 in 1 & 2.  For all intensive purposes though they are the same.

01.00:1 -------------------------------------------------------------------- / 28 / __ /15 / __ / 8.6 / 5.13
Rubicon NV3550 4:1--------------------------------------- / 66  / __ /38 / __ / 22 /16 / 9.5 / 5.6 / 4.10
02.72:1 ----------------------------------------------- / 78 / __ / 42 / __ / 28 / 23 / 15 / 13 / 8.6 / 5.13
03:00:1 ---------------------------------------------- / 86 / __ / 47 / __ / 28 / 25 / 15 / 15 / 8.6 / 5.13
04.00:1 ----------------------------------------- 115 / __ / 62 / __ / 34 / 28 / 20 / 15 / __ / 8.6 / 5.13
04.30:1 -------------------------------- / 124 / ___ / __ / 67 / __ / 36 / 28 / 22 / 15 / __ / 8.6 / 5.13
Scott's AX-5 6.7:1 -------------- / 141 / ___ / ___ / 84 / 57 / 52 / 36 / 34 / 21 / 14 / 12 / 7.5 /5.38
05.00:1 --------------------------/ 144 / ___ / ___ / 78 / __ / 44 / __ / 28 / 26 / 15 / __ / 8.6 / 5.13
11.70:1 ------------- /337/ 182 / ___ / ___ / 100 / 78 / 60 / 42 / __ / 28 / 23 / 15 / 13 / 8.6 / 5.13

What I've noticed is that when you switch down from say, 11.70 3rd & 4th gears basically overlap 4.3 in 1st & 2nd with the 1st and 2nd numerically lower.  And it continues with 2.72 and 1:1.

4.3:1 would match with a stock Rubicon though it's not account for the additional 95 lbs-ft of torque.  Which the 5:1 would probably make up for.  Also, it looks like the 11.70:1 isn't that good matchup and that the 10.34 might be better.  But that's 3.8:1 and the ratios between 2.72 and 3.8 are going to get a lot closer.

Actually let's do this a different way.  Lets think of gears as torque multipliers instead.  235lbs-ft for the 4.0L.  Using a TJ Rubicon as an example that's 15.454.54 lbs-ft.  Now if you swap that 4.0L for a 2.5L without changing anything else that's 9864.6.  Here's some additional combos.  This of course is assuming the tires are the same across the board.

AX-5 x 3.92 x 4.11 = 2416.7
AX-15 x 3.83 x 3.75 = 3375.2
NV3550 x 4.01 x 4.1 = 38636
AX-5 x 2.72 x 4.11 = 6573.4
AX-5 x 2.72 x 4.56 = 7293.1
AX-5 x 5 x 4.56 = 13406.4
AX-5 x 5 x 5.13 = 15082.2
NV3550 x 4 x 4.1 = 15454.5
NV4500 x 4.3 x 5.13 = 18562.6
AX-5 x 6.7 x 5.38 = 21195.1
NV4500 x 5 x 5.13 = 21584.5

On another note, I've been playing around with this site. https://www.blocklayer.com/rpm-gear.aspx  Great for comparing R&P and Tire sizes, too.  This should show stock AX-5, NV3550 and NV4500 already entered into it. https://apx6u.app.goo.gl/CJpt

Looks like 5.13's should be the perfect choice for 33's when accounting for an additional weight.  5.38's for 35's is within 1 mph too.  Anyway...  You can also add in the transfer case ratio.

[FourbangerYJ]

So, with an AX-5 and 5.38's a 4:1 would look like this; 84/50/31/21 which is closer to 2.72

Here's the gear spread for a NV4500 with 5.13's which is what I'm planning on running.  I've spaced the ratios out so they kinda line up respectively.  This includes 1:1 in the transfer case which are generally the 3 lowest (numarically) numbers then the 5th. The Rubicon's 4:1 in 4th is the same as 1st in 1:1 so I omitted one.

I threw in your ratios into the chart.  Interesting thing is 3 & 4 in 6.74:1 are actually marginally higher (numarically lower) then 2.72:1 in 1 & 2.  For all intensive purposes though they are the same.

01.00:1 -------------------------------------------------------------------- / 28 / __ /15 / __ / 8.6 / 5.13
Rubicon NV3550 4:1--------------------------------------- / 66  / __ /38 / __ / 22 /16 / 9.5 / 5.6 / 4.10
02.72:1 ----------------------------------------------- / 78 / __ / 42 / __ / 28 / 23 / 15 / 13 / 8.6 / 5.13
03:00:1 ---------------------------------------------- / 86 / __ / 47 / __ / 28 / 25 / 15 / 15 / 8.6 / 5.13
04.00:1 ----------------------------------------- 115 / __ / 62 / __ / 34 / 28 / 20 / 15 / __ / 8.6 / 5.13
04.30:1 -------------------------------- / 124 / ___ / __ / 67 / __ / 36 / 28 / 22 / 15 / __ / 8.6 / 5.13
Scott's AX-5 6.7:1 -------------- / 141 / ___ / ___ / 84 / 57 / 52 / 36 / 34 / 21 / 14 / 12 / 7.5 /5.38
05.00:1 --------------------------/ 144 / ___ / ___ / 78 / __ / 44 / __ / 28 / 26 / 15 / __ / 8.6 / 5.13
11.70:1 ------------- /337/ 182 / ___ / ___ / 100 / 78 / 60 / 42 / __ / 28 / 23 / 15 / 13 / 8.6 / 5.13

What I've noticed is that when you switch down from say, 11.70 3rd & 4th gears basically overlap 4.3 in 1st & 2nd with the 1st and 2nd numerically lower.  And it continues with 2.72 and 1:1.

4.3:1 would match with a stock Rubicon though it's not account for the additional 95 lbs-ft of torque.  Which the 5:1 would probably make up for.  Also, it looks like the 11.70:1 isn't that good matchup and that the 10.34 might be better.  But that's 3.8:1 and the ratios between 2.72 and 3.8 are going to get a lot closer.

Actually let's do this a different way.  Lets think of gears as torque multipliers instead.  235lbs-ft for the 4.0L.  Using a TJ Rubicon as an example that's 15.454.54 lbs-ft.  Now if you swap that 4.0L for a 2.5L without changing anything else that's 9864.6.  Here's some additional combos.  This of course is assuming the tires are the same across the board.

AX-5 x 3.92 x 4.11 = 2416.7
AX-15 x 3.83 x 3.75 = 3375.2
NV3550 x 4.01 x 4.1 = 38636
AX-5 x 2.72 x 4.11 = 6573.4
AX-5 x 2.72 x 4.56 = 7293.1
AX-5 x 5 x 4.56 = 13406.4
AX-5 x 5 x 5.13 = 15082.2
NV3550 x 4 x 4.1 = 15 454.5
NV4500 x 4.3 x 5.13 = 18562.6
AX-5 x 6.7 x 5.38 = 21195.1
NV4500 x 5 x 5.13 = 21584.5

On another note, I've been playing around with this site. https://www.blocklayer.com/rpm-gear.aspx  Great for comparing R&P and Tire sizes, too.  This should show stock AX-5, NV3550 and NV4500 already entered into it. https://apx6u.app.goo.gl/CJpt

Looks like 5.13's should be the perfect choice for 33's when accounting for an additional weight.  5.38's for 35's is within 1 mph too.  Anyway...  You can also add in the transfer case ratio.

It's very fascinating looking at all the numbers!
Thanks for running my numbers, I had not done that yet.
Looks like a 5.0 would put you very close to my current set up. But with no ability to run the 2.7. So it would depend on the trails you mostly run. If you do a lot of mild stuff the 5.0 is pretty low. Makes for slow going on easy stuff.
But you would have a very strong setup!

[Jeffy]

It's very fascinating looking at all the numbers!
Thanks for running my numbers, I had not done that yet.
Looks like a 5.0 would put you very close to my current set up. But with no ability to run the 2.7. So it would depend on the trails you mostly run. If you do a lot of mild stuff the 5.0 is pretty low. Makes for slow going on easy stuff.
But you would have a very strong setup!

Well from the chart, 5:1 + NV4500 gear spread follows 2.72:1 + AX5 pretty closely while giving you 144:1 at the top.  Giving up 13:1 for 144:1 seems like a good trade off since there's 15:1

02.72:1 ---------------------------------------------- / 78 / __ / 42 / __ / 28 / 23 / 15 / 13 / 8.6 / 5.13
05.00:1 --------------------------/ 144 / ___ / ___ / 78 / __ / 44 / __ / 28 / 26 / 15 / __ / 8.6 / 5.13

Keep in mind that the numbers are in order of the ratios and not gears.  What that means if you have to shift into 3rd, you're probably better off shifting to 4Hi and then going back into 1st.  It was pretty predictable across the board even with a doubler.

So for you, it would look like this;

3.92 x 6.75:1 = 142.3
2.33 x 6.75:1 = 87
1.44 x 6.75:1 = 52.3
1.00 x 6.75:1 = 36

3.92 x 2.72:1 = 57.4
2.33 x 2.72:1 = 34.1
1.44 x 2.72:1 = 21.1
1.00 x 2.72:1 = 14.6

3.92 x 2.48:1 = 52.3
2.33 x 2.48:1 = 31
1.44 x 2.48:1 = 19.2
1.00 x 2.48:1 = 13.3

3.92 x 1:1 = 21.1
2.33 x 1:1 = 12.5
1.44 x 1:1 = 7.7
1.00 x 1:1 = 5.38

Looks like there's a few different ways you could go about rowing gears.  The simplest would be to just start off in 4th and 6.7.  Anything faster than that and you might as well just be in 1:1

[FourbangerYJ]

Well from the chart, 5:1 + NV4500 gear spread follows 2.72:1 + AX5 pretty closely while giving you 144:1 at the top.  Giving up 13:1 for 144:1 seems like a good trade off since there's 15:1

02.72:1 ---------------------------------------------- / 78 / __ / 42 / __ / 28 / 23 / 15 / 13 / 8.6 / 5.13
05.00:1 --------------------------/ 144 / ___ / ___ / 78 / __ / 44 / __ / 28 / 26 / 15 / __ / 8.6 / 5.13

Keep in mind that the numbers are in order of the ratios and not gears.  What that means if you have to shift into 3rd, you're probably better off shifting to 4Hi and then going back into 1st.  It was pretty predictable across the board even with a doubler.

So for you, it would look like this;

3.92 x 6.75:1 = 142.3
2.33 x 6.75:1 = 87
1.44 x 6.75:1 = 52.3
1.00 x 6.75:1 = 36

3.92 x 2.72:1 = 57.4
2.33 x 2.72:1 = 34.1
1.44 x 2.72:1 = 21.1
1.00 x 2.72:1 = 14.6

3.92 x 2.48:1 = 52.3
2.33 x 2.48:1 = 31
1.44 x 2.48:1 = 19.2
1.00 x 2.48:1 = 13.3

3.92 x 1:1 = 21.1
2.33 x 1:1 = 12.5
1.44 x 1:1 = 7.7
1.00 x 1:1 = 5.38

Looks like there's a few different ways you could go about rowing gears.  The simplest would be to just start off in 4th and 6.7.  Anything faster than that and you might as well just be in 1:1

Ya thats a good point. I have done that a number of times!

[Jeffy]

I should also state that if I was keeping the AX-5, then the 11.70 would be a no brainer.  You lose about 2" over a SYE but are still longer than stock which is around 15".  I'm using a 19".  For the front the difference is a fraction of an inch and not an issue.  There's still a chance I might just keep the AX-5 but mine's a bit notchy.  Syncro's are bad in 1st and 2nd but not a problem.  The AX-5 to NV4500 swap requires a 1" adapter for internal slaves so that's something to consider as well.  Best case would be to swap the whole bellhousing for an external setup but that's more $$$.

[FourbangerYJ]

Well after putting some miles on the Black Box. It works well. I was surprised how much I did with just the 2.7. Way more than I thought. Overall pretty pleased. But I still think a 2.7 and a 4.0 combo would be best of all worlds. With the AX5.

[Jeffy]

Well after putting some miles on the Black Box. It works well. I was surprised how much I did with just the 2.7. Way more than I thought. Overall pretty pleased. But I still think a 2.7 and a 4.0 combo would be best of all worlds. With the AX5.

But then the question is would you use the 11.70 any?

[FourbangerYJ]

But then the question is would you use the 11.70 any?

Probably not. But the 4.0 and 2.7 would be used a lot! Just not together much. That's really low. I think it's more about choices of gearing options vs having a super duper low gear.