Ideal Cruising RPM for 4.0 from Gearing - Page 2 - JeepForum.com

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post #16 of 25 Old 06-11-2011, 11:30 AM
Jerry Bransford
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Originally Posted by 1C41N0 View Post
Secondly, and finally, why is 2600-2700 RPM sought after for the 4.0 when the factory RPM limit is 3,000 RPM? Any input is appreciated, and I hope this thread helps someone else out too!
Yes 26-2700 is ideal for bigger tires like you are running. Where in the world did you hear or read that the factory rpm limit is only 3000 rpm? Your TJ's engine rpm limit is where the redline is on your tachometer which is well over 5K rpms.

And hopefully you went with the above solid advice to install 4.88 gearing which is ideal for 33" tires and the 42RLE transmission. 4.10 and 4.56 will produce rpms that are too low due to your transmission's ultra-low .69 overdrive gear ratio.


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post #17 of 25 Old 06-11-2011, 11:58 AM
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Although my LJ is not a DD I find cruising w/ overdrive engaged at hiway speeds and flat areas not all that uncomfortable. I have 5.13s, auto, and 37s. My rpms at 65 - 70 are about 2100 - 2250. Frankly, I don't like running at 70 mph plus although the rig runs out smooth and occaisionally I do it...I simply didn't built it to be a hiway cruiser. Again, I'm not on the hiway much at all with the LJ and sometimes I just run w/ overdrive disengaged cruising closer to 2550 rpms which sounds/feels ideal and puts me at 55 mph, which is a safer "jeep" speed imho.

I'd agree w/ JB, ideal rpms for cruising is 2500-2700. Hopefully you geared for your desired road speed, per/ JB, and geared your transfer case to your wheeling needs.
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post #18 of 25 Old 06-11-2011, 04:45 PM Thread Starter
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For starters I did take the advice (thanks everyone) and went with 4.88's to match my 33s. I also went with true-tracs front and rear. (My wife can't drive a vehicle with lockers, and we have a lot of snow/ice in Nebraska) and I deploy frequently (got back from another tour 45 days ago). So she has to be able to drive it. I couldn't go any lower with the gearing due to the Dana 30.

I haven't done anything with TC yet... beings it's a DD I don't really wheel (no mud or rock crawling at all) in it, but I love it for a hunting/trail rig (plenty of deep snow.

I thought my Jeep was governing out at 3k rpm in OD (did that once) to figure out what it was.

I live where it's pretty flat with a few hills, mainly we get a really strong mid-west wind. I drive home (5 hrs) about once or maybe twice a quarter. The speed limit fluctuates between 60-75 mph. On average I stick between 70 and 75 on the interstate, I have no need to go any faster than that.
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post #19 of 25 Old 06-12-2011, 08:40 PM Thread Starter
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Well, I got it back today and I'm impressed. I can tell I would not be happy if I went with 4.56 or anything like that.
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post #20 of 25 Old 06-12-2011, 08:59 PM
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post #21 of 25 Old 06-12-2011, 09:50 PM
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Ive got 4.88's on 33's and Im running 3K at 70 with the 5spd and get about 13 mpg, 4.10's maybe 4.56's would probably suit your DD needs better then 4.88's would and yes I know you have the AUTO so there is some differences but the 4.10's on 33's puts it back to a stock style set up at least for the 5 spd.

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post #22 of 25 Old 06-12-2011, 09:53 PM
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I really love how people post about what works for them without taking into consideration the needs of the person they are talking about. 5-speed and 42rle 4-speed auto.... very different things. I also love when people post about what someone else should do when that other person has already made their move.

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post #23 of 25 Old 06-12-2011, 10:55 PM
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Quote:
Originally Posted by LuckRider
I really love how people post about what works for them without taking into consideration the needs of the person they are talking about. 5-speed and 42rle 4-speed auto.... very different things. I also love when people post about what someone else should do when that other person has already made their move.
Reading comprehension?

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post #24 of 25 Old 06-12-2011, 11:05 PM
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Quote:
Originally Posted by 1C41N0 View Post
Well, I got it back today and I'm impressed. I can tell I would not be happy if I went with 4.56 or anything like that.
Glad you like the 4.88's because that is all that matters. Some folks might have similar or exact setups as you and their advice really helps while others have great experience and opinions. I've helped a few that PM'd me because I'm running exactly what they are thinking. Hell, I even sent them pics of my speedo and rpms to help them decide what is real life with their setup.

Go drive that thing now and enjoy it!!

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Last edited by Rubi4Us; 06-12-2011 at 11:06 PM. Reason: spelling
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post #25 of 25 Old 06-13-2011, 06:31 AM
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Quote:
Originally Posted by Unlimited04 View Post
thats the setup I have now and I like it. still sucks in the mountains, but not near as bad as 3.73s/31s.



This might help:
http://www.jeepforum.com/forum/f9/33...6/#post9838564
That linked post should be a sticky

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