How's the 3.7 compared to a ZJ's 4.0? - JeepForum.com

 
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post #1 of 15 Old 09-09-2012, 01:40 PM Thread Starter
cherox
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How's the 3.7 compared to a ZJ's 4.0?

Hey folks. I am looking to upgrade my ride and the KK is on my short list of potential vehicles.

Has anyone upgraded from a ZJ or WJ Grand Cherokee with the 4.0 I6 engine? What is your opinion of the power difference?

I ask because I have found both my ZJ and a friend's WJ can barely get out of their own way. I am wondering if it is as bad on the Liberty? Specifically I am referring to slight inclines on the highway and passing power.

Thanks so much from a Jeep lover and prospective KK owner!

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post #2 of 15 Old 09-09-2012, 03:16 PM
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Well I can tell you my wife's KK can get up and go better than my XJ. Granted, the XJ is turning 33x12.50s and steelies but the I6 is torquey and reliable while the 3.7 is smooth and quick - reliable to this point as well.

~Mike~


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post #3 of 15 Old 09-09-2012, 05:24 PM
streetglideok
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Towards the end of the run of the 4.0's, I started seeing reliability problems with the engine. To me, they felt almost anemic as well. Their power band was about 1k-2k rpm lower then the 3.7L, so though they had more low end torque relatively speaking, they flat out ran out of steam when you reached the midrange. I'm running a 6speed, with the stock 3.55 gears, and at 6000 feet I have no issues.
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post #4 of 15 Old 09-09-2012, 06:18 PM
tjkj2002
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The 3.7 actually retains oil instead of leaking it and requiring a new valve cover gasket,oil pan gasket,and rear main seal every 30k.

'02 Liberty sitting on 35" tires,HP44,RockJock60,and AtlasII t-case
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post #5 of 15 Old 09-09-2012, 07:07 PM
fosterjd79
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I have a 4.0 XJ, 4.7 WJ, and 3.7 KK in the driveway. Obviously the 4.7 doesn't matter here. The 3.7 is much peppier than the 4.0 but the compare is of a 113K mile 4.0 versus a 30K mile 3.7 so it's a tough sell. No disappointments in the 3.7 but it's no 4.7 and the gas mileage sucks on them all.
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post #6 of 15 Old 09-09-2012, 11:37 PM
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Quote:
Originally Posted by fosterjd79 View Post
I have a 4.0 XJ, 4.7 WK, and 3.7 KK in the driveway. Obviously the 4.7 doesn't matter here. The 3.7 is much peppier than the 4.0 but the compare is of a 113K mile 4.0 versus a 15K mile 3.7 so it's a tough sell. No disappointments in the 3.7 but it's no 4.7 and the gas mileage sucks on them all.
hah.....lol that's the only difference in your driveway and mine.

~Mike~


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post #7 of 15 Old 09-10-2012, 03:20 AM
TIJKK1220
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I had a 96 ZJ before I bought my KK and the differences I found were as follows.

The low end torque has lessened. I can no longer just put the jeep in drive and have it begin to crawl my rutted up driveway I have to tap the gas a little bit.
The KK tends to hold RPMs a lot longer than the 4.0 did but that may just be the computer trying to keep a "smoother" ride with less jerking around
Speed wise I think the KK has a little more mid/high range pep. Where the ZJ had a lot of pick up from a stop it seemed to peak a lot sooner than the kk does
(as a side note my poor ZJ was late in years and high in mileage and was missing overdrive later in life however I had driven it before it lost the gear)

Statwise the I6 has ~165 hp where the 3.7 is supposed to have ~210

All and all the difference is negligible the KK feels comfortable and familiar after owning a ZJ with the I6.

Edit: As for passing power. I have never had an issue passing someone even on an incline plenty of power to get up and go.
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post #8 of 15 Old 09-11-2012, 12:14 AM
Poncherello
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Well, I just had my Lib tuned up them dyno'd lol!
Attached Thumbnails
Dyno test.jpg  

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post #9 of 15 Old 09-13-2012, 05:29 AM
NedBraden55
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Sure you did, and I've got a two foot biological appendage.
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post #10 of 15 Old 09-14-2012, 12:03 AM
Poncherello
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LOL, this was from a friend of friend's 10' Camaro. My buddy is a big time gear head, had a 69 'Camaro back in highschool with a 327 11:1 compression ratio. When his friend got this car, it just brought him back in time. I wish I had 475 ftlbs of torque in my Lib. I don't think the tranny would handle it, not certain about the transfer case or the axles but I bet frame would have no issue, considering I have a solid roof.

When you get knee-deep in a situation, floor it.
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post #11 of 15 Old 09-14-2012, 01:16 PM
marlon_jbt
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475lb/ft of torque would grenade the entire drivetrain and turn the KK's body into a Twizzler.

Red Jeep Club member # 264
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post #12 of 15 Old 09-15-2012, 11:33 PM
Poncherello
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Drive train wouldn't handle it, but if you were to upgrade the drive train, you still think the chasis would have issues?

When you get knee-deep in a situation, floor it.
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post #13 of 15 Old 09-16-2012, 03:28 AM
marlon_jbt
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I'm actually not sure. It's just a theory of mine.

... it could possibly twist it to be unnoticeable to us, but if you were to measure it to 100ths of an inch, yes.

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post #14 of 15 Old 09-18-2012, 01:15 AM
Poncherello
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I might ask the guys on AllPar. Someone on there mentioned that the Lib's frame had higher torsional rigidity then the XJ. Not sure. I think a sunroof or the skytop may have some difficulty with twisting. Oh well.

When you get knee-deep in a situation, floor it.
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post #15 of 15 Old 09-18-2012, 11:55 AM
marlon_jbt
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That is true. It is a 3 layer unibody, vs the XJ's 2 layer. That's one reason why it weighs more.

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