People just have to understand where the power band is on this motor and use it. The TJ's 4L straight 6 was a low-revving, long-stroked tractor motor (yes, this is what it was originally designed for by AMC). The 3.8L V6 is an oversquare short-stroker & develops all it's power above 2500 RPM, so people just have to learn to go there & use it.

When I'm approaching a steep hill doing 70MPH on a freeway I begin to shift down a few ratios (I have a 6 speed manual with 3.21s), so that by the time I hit the incline & really need power, I'm in third, pulling 3000RPM and dont lose any speed. I'm talking those really steep hills where 22 wheelers are crawling up at 10mph and I need to back off the throttle in 3rd to keep it under 75MPH. And some people here seem to expect the JK's auto to stay in OD at like 1900RPM and sail up hills as if it had a Hemi in it; the last time I checked it was possible to switch an auto out of OD & even manually downshift into 3 or 2.

 

Never knew that. Got a source?

Here is a link to AllPar, about the 4.0L

http://www.allpar.com/mopar/40.html

 

Thanks for that; I stand corrected. I knew it was based on a 4 cylinder motor, but it was the newer 2.5 released in '84 & not the older one used in Willys Tractors

"...Its design actually stemmed from the 2.5L four-cylinder introduced in 1984, the first four-cylinder built and designed by AMC/Jeep (GM was responsible for the 2.8L V-6) "
[url]http://www.jpmagazine.com/techarticles/engine/154_0604_jeeps_kick_ass_engine_history_4_liter/the_90s.html


It was still based on older tecnology though as I originally stated, including a tall cylinder block with longer stroke and shared some architecture with the old Typhoon six from the early 60's, which is why it had good low-end torque but lacked the ability to rev freely and provide power at higher revs, unlike the JK.

"The 4.0, to save money on machine tools, used the same cylinder spacing as the 4.2 and 232-cid Typhoon engines, along with some other dimensions. It did have a longer stroke, achieved via a taller cylinder block deck height."
http://www.allpar.com/mopar/40.html

 

"kinda makes me wonder if it is just an offroad vehicle that someone said" hey, u guys think we can make it go on paved roads too!?"




EXACTLY........It does pretty good on the freeway and KICKS A$$ offroad....

 

i only have 1800 km on mine but i have to say, it is world of difference in comparasion to the 2.5l in my 91 yj. that I4 has nothing on this V6. what i do like though are these guys i see on youtube that have put 5.7l hemi's in their jk's that's awesome!

 

I really don't understand this I have a 4 door with 3.73 gears and auto trans, I've driven from canada to florida twice at highway speeds witch is 75 to 85 mph and its seen 100 mph passing cars on 2 lane highways, the 3.8 is an old engine that is time proven and the " jeep people " are not always kind to there engines and drive train parts, and chrysler does not want the warranty claims that come with high horse power that breaks things. then when all the other parts start to break everybody says that the jeep is a pile of junk. So we have a jeep that is no rocket but will take all the crap that we dish out.

 

I read this thread yesterday while considering a JKU auto with 3:73's (thought it had 4:10's until the dealer checked)...would it have enough power??? Well my buddy let me drive the jeep since last night. Power was fine! AND I'm coming out of a 4.0 TJ manual! I was on the turnpike heading to work doing 80+mph with no problems. No, it's not a rocket, but it worked fine for me. And it shifted nicer than I thought, I was just happy with the drivetrain all around.

I'll be a JK owner by the weekend .

 

Awesome! Come on over to the dark side!!!

 

We've been driving our JK from Baltimore cross country since June 7th making stops along the way. We are heading to LA. Got to Gallup NM tonight with no issues so far. Had to disengage the O/D going up to the top of the continental divide tho with me, the wife, kids, and a whole lotta luggage in the Jeep.

 

I loved it until a bearing self destructed and sent shards thru every engine orifice...had to get the engine replaced (and the warranty company was NOT cooperative, took almost 3 months...). Now I'm a bit skeptical on this one, less than one week and the check engine light is already on and I have an appt to get it back to the shop this weekend...grrrrr....