jk motor and kj motor

Sport · **Posted:** Mon Dec 15, 2008 12:02 pm

Aren't they basically the same motor? Reason I ask is I just found out that the JK has a super charger kit available for their motor. I wonder if it would work for us.

jeepkj02 · **Posted:** Mon Dec 15, 2008 12:09 pm

No. The engine in the JK is a 3.8L out of a minivan (Dodge Caravan?), the engine in our KJ is a 3.7L Powertech also found in the WK, XK, KK and other Dodge vehicles. Completely different animals!! Not compatible in any way.

tjkj2002 · **Posted:** Mon Dec 15, 2008 12:19 pm

JK's 3.8 V-6 = OHV,iron block and heads,been around since the early '90's

KJ's 3.7 V-6 = SOHC,iron block and alloy heads,brand new engine in '01(based off the 4.7 V-8 which was brand new in '99)

Fulltimer · **Posted:** Mon Dec 15, 2008 2:39 pm

How much would be involved in swapping a 4.0L from a Wrangler into the KJ? Just curious.

Terry

tommudd · **Posted:** Mon Dec 15, 2008 2:46 pm

besides wiring harness, computer, fuel pump, extra length of the 4.0 over the 3.7, not much :lol:

about like any engine swap,
but if you are going to do a swap why the heck a 4.0?

jeepkj02 · **Posted:** Mon Dec 15, 2008 3:21 pm

Fulltimer wrote:

How much would be involved in swapping a 4.0L from a Wrangler into the KJ? Just curious.

Terry

It would be easier to swap in a 4.7L V8, basically the same motor with 2 cylinders chopped off.

Sir Sam · **Posted:** Mon Dec 15, 2008 4:34 pm

Fulltimer wrote:

How much would be involved in swapping a 4.0L from a Wrangler into the KJ? Just curious.

Terry

While the 4L is a rock solid motor with great reliability and longevity it is a poor match for a swap into a JK. Nothing would b easy about, putting in a chevy 350 with MPI would be just as "easy" as a 4L swap.

Maximum Carnage · **Posted:** Mon Dec 15, 2008 5:00 pm

jeepkj02 wrote:

The engine in the JK is a 3.8L out of a minivan (Dodge Caravan?)

This is funny :-)r

tjkj2002 · **Posted:** Mon Dec 15, 2008 5:04 pm

Maximum Carnage wrote:

jeepkj02 wrote:

The engine in the JK is a 3.8L out of a minivan (Dodge Caravan?)

This is funny :-)r

'03+ KJ's have the same "minivan" trans also(just slightly updated though) :wink:

.

Jeepjeepster · **Posted:** Mon Dec 15, 2008 5:48 pm

I would rather have a minivan tranny that is updated rather than a engine straight out of a minivan.

4.7 would be a better match over the 4.0 in the kj. You would be going from the same torque and hp to the same torque and hp only at slightly lower rpms... Cant think of anything that would make sense with that swap.

4.0 is too long to fit anyway.

daspes · **Posted:** Mon Dec 15, 2008 8:25 pm

I'll say that after 4,000 miles now, the JK engine isn't all bad. It is not underpowered, it just doesn't have as much power as you want. It gets you where you want, but never makes you go "woohoo!!!".

InCommando · **Posted:** Tue Dec 16, 2008 2:09 pm

The 3.7L has also been the base motor in the Ram 1500 for years.

I have had 3 minivans with the 3.8, and the new one has the 4.0 V6. Night and day differrence in those two. Jeep should have used the 4.0 V6 in the JK.

I recently drove a JK 2dr with a 6spd. While not hateful, a prefer the KJ 3.7. I would really worry about the 3.8 in an Unlimited.

I cannot find it at the moment, but I saw a chart comparing the power bands of the 3.7L & 4L I6 a couple of years ago. There is not that big of difference, even "down low" where everyone claims to feel the difference. The 3.7 was the better of the two. I do not feel that the 3.7 is giving up anything to the I6 other than the aftermarket availabilty of parts. Remember that the KJ is hundreds of pounds heaver, taller, wider, longer, etc.... than an XJ.

Funny, I do not recall the NSG370 being available in the minivan???? :shock:

jeepkj02 · **Posted:** Tue Dec 16, 2008 2:21 pm

InCommando wrote:

Funny, I do not recall the NSG370 being available in the minivan???? :shock:

I don't think any minivan (from any mfg) came with a stick. Don't think soccer moms know how to drive a manual. HAHAHA!! :lol:

daspes · **Posted:** Tue Dec 16, 2008 2:52 pm

InCommando wrote:

Funny, I do not recall the NSG370 being available in the minivan???? :shock:

I'm sure he was refering to the Atuo (42RLE).

Prospect62 · **Posted:** Tue Dec 16, 2008 6:22 pm

jeepkj02 wrote:

I don't think any minivan (from any mfg) came with a stick. Don't think soccer moms know how to drive a manual. HAHAHA!! :lol:

Funny you should say that, I just saw this on CL while browsing around the other day...

http://syracuse.craigslist.org/cto/957493851.html

Also, I would LOVE to be the first guy to do a 4.7L swap. It would be awesome to have the V8 and my 5-speed. Mmmmm...yeah. You can send donations to...

ATXKJ · **Posted:** Tue Dec 16, 2008 8:46 pm

InCommando wrote:

I cannot find it at the moment, but I saw a chart comparing the power bands of the 3.7L & 4L I6 a couple of years ago. There is not that big of difference, even "down low" where everyone claims to feel the difference. The 3.7 was the better of the two.

If you find the graph - check the rpm ranges - normally they plot 2-3000 rpm up and where the inline 6's really shine are just off-idle - about 600-800 rpm - when you're in 4low trying to creep along - that's when the difference shows.
on the street the v6 is better.

InCommando · **Posted:** Thu Dec 18, 2008 2:11 am

Having actually creeped in a 3.7, there is no lack of off-idle power. Perhaps it is the 6spd making the most use of it?

I have looked at dozens of postings on this through google. All I have found is people talking up the 4L I6 & downing the 3.7L without ever proving anything: it is just something they : know." :roll:

Here is a prime example of the misinformation & BS on the subject:

http://www.jeepforum.com/forum/showthread.php?p=4856658

Those einsteins can't keep the 3.7L & 3.8L seperated in their pea brains with one idjit claiming to have owned a "3.8L " KJ for 3 years ( he apparently never opened the hood or looked at the tailgate.... ) Others are confused over the 4.0L V6 & the 4.0L I6. Many talk crap, but again offer no support for their position. I also found a guy who swears a 3.7 cannpt break 4,500 RPM's "on its best day, even in neutral." Well, he needs to come for a little ride. And BTW: the fuel shuts of at 107 MPH....

A number I have run across is that the 3.7L has 185#'s at 1,200 rpm. As that is not too far off 4.0L i6's max torque for some years, I'd say that people who do not think the 3.7L develops usable torque are either driving ill-equipped versions or are going by what everyone "knows" while ignoring the evidence in front of them. Both engines reach max tq at the same RPM: 4,000 . While the 3.7 gives you 235, the XJ 4L I6 gave you a max of 220. for all but the last 3 model years

This also reminds me of a KJ NSG370 question: I have read were it is the "wide ratio" version & has a 5.0 1st gear. But some say it is the close ratio version like was used in a TJ. As the wide ratio version is mated to the 3.7 in the Dakota & the Ram, while the close-ratio was used ( at the time) behind the 4L in a TJ, it makes sense to me that all of the 3.7 version would have the 5.0 first gear. My owner's manual has been MIA since about the 2nd month I owned my KJ : maybe the info was in that?

I'll keep looking from this end. But in the meantime, can any of the people who "know" these things post up the info for us inquiring minds?

Guest · **Posted:** Wed Dec 24, 2008 1:58 pm

It's funny how often I hear that the 4.0 makes more usable torque than the 3.7.

my KJ is significantly more powerful than any XJ, according to my precision-calibrated seat-of-the-pants dyno. And it doesn't leak from every mating surface either. Could the KJ use an infusion of 4.7 power? Absolutely, and the XJ should've had a 318, too. They're both dogs on the interstate, but the KJ is much more livable and feels like it's got a little more midrange meat.

As far as not being able to go past 4500 in neutral...

It's called a rev limiter!

And, on-topic, to the OP:

I wish my KJ had the minivan 3.8, to be honest. the KJ's 3.7 is good, IMO, but the 3.8 I think would be a better engine for the KJ, and it's got a little bit longer history behind it as being a bulletproof engine (Go figure...put an engine in a minivan that's going to be neglected...it's gotta be a bulletproof mill)

Diggerfreek · **Posted:** Wed Dec 24, 2008 3:21 pm

just to go off topic one more time, the kk cuts fuel at 112 to 115. also, i have taken many vehicles off of the line with much lager engines and taken them on the highway

jeepkj02 · **Posted:** Wed Dec 24, 2008 3:55 pm

tjkj2002 wrote:

Maximum Carnage wrote:

jeepkj02 wrote:

The engine in the JK is a 3.8L out of a minivan (Dodge Caravan?)

This is funny :-)r

'03+ KJ's have the same "minivan" trans also(just slightly updated though) :wink:

.

Didn't know there were any RWD minivans, thought all of them where FWD.

jk motor and kj motor

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