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I am planning on buying a JK Rubicon unlimited in the very near future. I have test driven one with manual trans and was terribly disappointed with the 3.8L minivan motor they are putting in them.

I've been reading posts here and I see people are putting 35" and 37" tires on them. So it looks like there isn't much problem with this engine off road? Opinions?

I will probably just want to run 33"s
 
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I think it's fine offroad. I have the Rubicon which has the 4:1 transfer case so it provides fairly low gearing right out of the box. I run 35's and changed my diff gears to 4.88's, which gives me slightly lower overall gearing than I had when stock.

I think you'll find that this engine revs higher than than the 4.0 inline 6 and sounds more "buzzy". If you can tolerate that, it's not too bad. Depending on the type of offroad driving you plan on doing, you'll mostly be travelling pretty slow and if you get your overall gearing set properly for your tire size, I don't think you'd be disappointed with its performance.
 

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I run 37's and 4.88's and have no issues on or off-road. I've yet to even get close to running out of power off-road, and on the street it does just fine. I live where it's flat, and 5.13's would be better choice for those in hilly areas.
 
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I’m running 37’s and 5.13’s and regularly drive on I-70 in Colorado and have no issues on or off road.
 

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Also, keep in mind when you test drive one, the computer is still in a learning phase. The engine actually comes to life a little after the first 1000 miles or so. I know it sounds fictitious, but most of these guys will tell you they did notice a difference. It could be that we all just got used to it. :)

I'm running 37's with 4.10 gears. I have an automatic and it does fine as long as I turn the overdrive off. I will be adding 5.38 gears when they are released, but for not I get around OK.
 

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Discussion Starter #6
Rotorhead mentioned driving an Auto Trans.. I ran into a man with a well modified 2007 JK near Lancaster CA and he did mention that he had to add a trans cooler to his. I did'nt talk to him long enough to find out under what circumstances he ran into overheading problems.

I will probably buy a manual. The deley in shifting autos drives me nuts. Been driving a manual for 25 years. ITs second nature to me now.
 

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I added a cooler to mine, but only because I tow a 3000 lbs camper. I think it's a good idea anyway, but hey that's the cheapest mod I've done. I spent about $50 at summit racing. Don't let that be a deciding factor. Get what you want.
 

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I am planning on buying a JK Rubicon unlimited in the very near future. I have test driven one with manual trans and was terribly disappointed with the 3.8L minivan motor they are putting in them.

I've been reading posts here and I see people are putting 35" and 37" tires on them. So it looks like there isn't much problem with this engine off road? Opinions?

I will probably just want to run 33"s
I think the motor is plenty powerful (I still have the stock 32s, but have added a little weight), as I detailed in a long winded post in this thread: http://www.jkowners.com/forum/showthread.php?t=1148

That said, if you were "terribly disappointed" with the stock 32s, you are likely to be even more unhappy after installing 33s. One option would be to regear to 4.56s or 4.81s. Or, if you've got 20 large lying around, do a hemi swap!
 

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See if you can find a used one to test drive. There really is a difference between a broken in JK and one with only a few miles on it. I noticed a change in mine power wise and economy wise at about 1500 miles. A muffler change helped a little, too. Mine still has the stock rubber and is my daily driver. No regrets at all. It is plenty of engine off road for my usage (desert mostly.) I have a few hills on my 72 mile round trip commute. If I throw on the CC at 66mph, I stay at 2000rpm's all the way home. A little more or less, and the tranny wants to down shift on the hills. Oh, mine's a Rubicon Unlimited.
 

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My opinion applies to the modified/lifted/big tire world. I think its just ok in the city, just ok off highway, but I think it just flat out sucks on the highway.

In factory form, I think its just ok in all areas.

Shoulda put the 4.7L in it from the get go
 

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My opinion applies to the modified/lifted/big tire world. I think its just ok in the city, just ok off highway, but I think it just flat out sucks on the highway.

In factory form, I think its just ok in all areas.

Shoulda put the 4.7L in it from the get go
I will TOTALY agree with you on this one. My wife and I are looking at an unlimited Rubi for her.. but she has NO clue how to drive stick, so it's looking like an auto.. Well I test drove a 6 speed manual, and it was OK... for the test drive at least. They NEEd AT least the 4.7 V8 in it... or a diesel :) one of those and I'll buy it!!! PERIOD
 

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I hate the motor and miss my 4.0L. The motor is definately different. I have been running 37's with 4:10s and the thing is a dog. I will be getting my Jeep back this weekend and interested to see how the 5:13's will work. As for offraod, I have no complaints, I still am getting use to an auto. Good luck.
 

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Funny,

Personally I can't wait for the huge power increase I will get when I get an 09 Wrangler and get rid of my Suzuki Samurai. You guys should try cruising around with 64 screaming horses under the hood.
 
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