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Old 12-20-2013, 09:44 PM   #1
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Advantage: stock 3.6 or upgraded 3.8

I'm leaning heavily toward a new JKU to replace my TJ (4-month-old+80lb lab won't fit in a TJ, sadly). However, I've got a pretty good connection to get a heck of a deal on an older JKU. I've driven a stock JK with a manual and the 3.8, and the lack of bottom end torque just isn't going to cut it for me. I realize there's more torque and more HP than my 4.0, but I'm not into revving up my Jeep to get to the power.

SO - am I better off with a new one to get that 3.6 (I've test driven, and it will make me happy), or are there upgrades available for the 3.8 that may make me happy (supercharger or something else)? Specifically, I want linear power at low RPMs. An auto trans is absolutely not an option.

I drive 38 miles each way to work - super-low gearing isn't an ideal solution either. My TJ has 3.73s and a 6-speed, and it's perfect. I'm far from a speed demon in the Jeep - in fact, relaxed driving is one of the things I love about it. All I want is to feel power early. When called upon, the TJ will chirp the tires in each of the first three gears. Is that too much to ask?

Any advice is greatly appreciated. Especially if your brain works like an engineer's...

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Old 12-20-2013, 10:57 PM   #2
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3.6 all the way. 3.8 was gutless and even with super charger is not up to spec. Many of us waited for the 3.8 to be replaced for a reason. You drove it, you loved it. Dont spend 5k supercharging a used 3.8. Put it towarss a newer 3.6.

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Old 12-21-2013, 12:11 AM   #3
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3.6 all the way. 3.8 was gutless and even with super charger is not up to spec. Many of us waited for the 3.8 to be replaced for a reason. You drove it, you loved it. Dont spend 5k supercharging a used 3.8. Put it towarss a newer 3.6.

I have to agree. Sinking $5,000 in a used Wrangler to boost the power, that would be money wasted that could be well spent on a new one. JMO
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Old 12-21-2013, 12:32 AM   #4
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You want low end. Neither the 3.6 or 3.8 are going to cut it stock. A lot of it has to do with the drive by wire throttle in all JK's. I drove a Tj for over 10 years, A YJ for 3 and loved the 4.0. The electronic throttle was very hard to get used to in my 07. Eventually tuned the engine and bought a Sprintbooster. Both made a marked improvement. The 3.8 auto 4 door is the absolute worst. People would be surprised, my 07 2 door w/ 35's actually does well on road. 4:88's will get me back go stock or slightly better, but most important ... Slow crawl speed.

You do not have to spend $5000 on a supercharger. Regearing the axles ($1000-$2000) is the better bet to get the jeep to move.

Good luck The 3.8 and 3.6 are both small engine that require higher revs to move. This was also something I had to get used to.
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Old 12-21-2013, 12:56 AM   #5
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The 3.6 has an advantage of lower rpm torque, more torque throughout the rpm range, and a larger rpm range. This improves crawling characteristics and maximum acceleration. The low rpm torque isn't a massive increase but it makes it easier to start on hills with a manual. However, the top end puts down about 50% more power when shifting at peak horsepower. Definitely way better for highway passing and merging onto freeways. You'd have to add about 150hp on the top end of a 3.8 to match the 3.6.

However, when it comes to normal everyday driving, the power difference isn't that much. This is especially true with a manual, shifting around 3000-4000 rpm. In the city, you wouldn't feel a huge difference between the two engines with a manual. The auto is tuned much better to the 3.6l output. The manual gearing isn't ideal with the 3.6. The gear ratios are too close, and it would require you to either shift at really low rpms, or really high rpms, to feel the true gains of the 3.6 over the 3.8. You notice the difference for crawling slightly about idle, and redline shifting acceleration.

Hands down, the 3.6l delivers better for low speed, low rpm crawling, and has the power to maintain speed, and accelerate like a madman on the highway.

So unless you drive a lot of highway and want the extra power for passing, and slight low rpm gains, it probably won't matter which one you pick. If you were going with a auto, the 3.6l is the only choice.
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Old 12-21-2013, 12:59 AM   #6
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Originally Posted by redneckwelder View Post
The 3.6 has an advantage of lower rpm torque, more torque throughout the rpm range, and a larger rpm range. This improves crawling characteristics and maximum acceleration. The low rpm torque isn't a massive increase but it makes it easier to start on hills with a manual. However, the top end puts down about 50% more power when shifting at peak horsepower. Definitely way better for highway passing and merging onto freeways. You'd have to add about 150hp on the top end of a 3.8 to match the 3.6. However, when it comes to normal everyday driving, the power difference isn't that much. This is especially true with a manual, shifting around 3000-4000 rpm. In the city, you wouldn't feel a huge difference between the two engines with a manual. The auto is tuned much better to the 3.6l output. The manual gearing isn't ideal with the 3.6. The gear ratios are too close, and it would require you to either shift at really low rpms, or really high rpms, to feel the true gains of the 3.6 over the 3.8. You notice the difference for crawling slightly about idle, and redline shifting acceleration. Hands down, the 3.6l delivers better for low speed, low rpm crawling, and has the power to maintain speed, and accelerate like a madman on the highway. So unless you drive a lot of highway and want the extra power for passing, and slight low rpm gains, it probably won't matter which one you pick. If you were going with a auto, the 3.6l is the only choice.
I was under the impression low speed crawling would be very close between the two. Not quite understanding you here ?
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Old 12-21-2013, 02:35 AM   #7
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The description above sounds too complicated. The SC does do much other than make a loud whining noise below 2500 RPM. If you use are used to driving a 2 stoke engine or redlining your Jeep then you will love the 3.8 with the SC.
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Old 12-21-2013, 04:33 AM   #8
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Just remember, that you are going from a TJ to a JKU, which is considerably HEAVIER!
And now you have 2 more passengers, verse the 2 door JK, and you have added even more weight!
So you need as much engine as possible to get that extra mass of weight in motion.

I agree with Kjeeper10, that the 4 door 3.8 is the worst......

I also went from a TJ 4.0 3:73, but mine was auto. I road tested several used ones including the 4 doors 3.8, used and a 3.6 4 door new. I would have never been happy with the 3.8 4 door, because the ratio of power to weight mass, just didn't cut it for me........

So I highly recommend for your type of driving, the 3.6 engine, with the 3:73 ratio as minimum, or even the 4:10 as better.......
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Old 12-21-2013, 07:33 AM   #9
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Just remember, that you are going from a TJ to a JKU, which is considerably HEAVIER! And now you have 2 more passengers, verse the 2 door JK, and you have added even more weight! So you need as much engine as possible to get that extra mass of weight in motion. I agree with Kjeeper10, that the 4 door 3.8 is the worst...... I also went from a TJ 4.0 3:73, but mine was auto. I road tested several used ones including the 4 doors 3.8, used and a 3.6 4 door new. I would have never been happy with the 3.8 4 door, because the ratio of power to weight mass, just didn't cut it for me........ So I highly recommend for your type of driving, the 3.6 engine, with the 3:73 ratio as minimum, or even the 4:10 as better.......
I hadn't thought of the weight of the 4-door vs. the 2-door - the 3.8 JK I drove and couldn't deal with was actually a 2-door. To think a 4-door would be even worse - yikes!

But remember - I already knew a stock 3.8 wouldn't cut it for me. I would mod the engine (SC or otherwise) to make it have better low end power. But it sounds like the consensus it that it's not worth it. Unless maybe I can find one with a bad motor *really* cheap and drop in either a V8 or a diesel...now I'm really dreaming!
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Old 12-21-2013, 07:47 AM   #10
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I had an '88 YJ that I swapped the H.O 4.0 from a TJ into, so I know kind of what you're used to. The carbureted 4.2 that was in it absolutely sucked.

Fast forward a number of years and I find myself in an '07 JKU Sahara 6 speed. Kind of gutless with the 3.21 gearing. Then added 34" rubber and some armor and a bumper and winch....well we all know how that goes. Replaced that with a 2013 JKU Rubicon. 3.73's and auto. Put all the goodies from my '07 on it and 35's. I have NO issues at all with how this Jeep drives, both city, highway or offroad.

With the '07 I was planning on gears and a Ripp SC as it was just too underpowered. With my '13, I get in, turn the key and drive. No thoughts whatsoever about gears or power adders. If you can swing a '12 or newer, it's really the best option based on what you say you want.
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Old 12-21-2013, 08:01 AM   #11
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Originally Posted by redneckwelder View Post
The 3.6 has an advantage of lower rpm torque, more torque throughout the rpm range, and a larger rpm range. This improves crawling characteristics and maximum acceleration. The low rpm torque isn't a massive increase but it makes it easier to start on hills with a manual. However, the top end puts down about 50% more power when shifting at peak horsepower. Definitely way better for highway passing and merging onto freeways. You'd have to add about 150hp on the top end of a 3.8 to match the 3.6.

However, when it comes to normal everyday driving, the power difference isn't that much. This is especially true with a manual, shifting around 3000-4000 rpm. In the city, you wouldn't feel a huge difference between the two engines with a manual. The auto is tuned much better to the 3.6l output. The manual gearing isn't ideal with the 3.6. The gear ratios are too close, and it would require you to either shift at really low rpms, or really high rpms, to feel the true gains of the 3.6 over the 3.8. You notice the difference for crawling slightly about idle, and redline shifting acceleration.

Hands down, the 3.6l delivers better for low speed, low rpm crawling, and has the power to maintain speed, and accelerate like a madman on the highway.

So unless you drive a lot of highway and want the extra power for passing, and slight low rpm gains, it probably won't matter which one you pick. If you were going with a auto, the 3.6l is the only choice.
Actually at the low end, both are equal. It's the mid to upper end of the curve where the 3.6 has the advantage.
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Old 12-21-2013, 08:02 AM   #12
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I was under the impression low speed crawling would be very close between the two. Not quite understanding you here ?
You are correct, as usual.
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Old 12-21-2013, 08:03 AM   #13
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you want low end. neither the 3.6 or 3.8 are going to cut it stock. A lot of it has to do with the drive by wire throttle in all jk's. I drove a tj for over 10 years, a yj for 3 and loved the 4.0. The electronic throttle was very hard to get used to in my 07. Eventually tuned the engine and bought a sprintbooster. Both made a marked improvement. The 3.8 auto 4 door is the absolute worst. People would be surprised, my 07 2 door w/ 35's actually does well on road. 4:88's will get me back go stock or slightly better, but most important ... Slow crawl speed.

You do not have to spend $5000 on a supercharger. Regearing the axles ($1000-$2000) is the better bet to get the jeep to move. Good luck

the 3.8 and 3.6 are both small engine that require higher revs to move. This was also something i had to get used to.
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Old 12-21-2013, 08:19 AM   #14
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Old 12-21-2013, 08:51 AM   #15
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I hadn't thought of the weight of the 4-door vs. the 2-door - the 3.8 JK I drove and couldn't deal with was actually a 2-door. To think a 4-door would be even worse - yikes!

!
Yes, the 4 door is about 400 lbs more than the two door. And then figure if you have two more passengers on occasions, well there is another 300-to 500 lbs.
It just takes a lot more engine to move all of that additional weight!

Good Luck in your Decision, and have a
MERRY CHRISTMAS, and a HAPPY NEW YEAR!!!!!!!
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Old 12-21-2013, 08:55 AM   #16
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The biggest difference between the 3.6 and 3.8 is the factory gearing. 3.8 auto specifically is way under geared AAMOF a 3.8 with 4.88 is compatible to the factory 3.6 with 4.10. As for torque they are very close and I guarantee that they are so close that once you match the proper gear ratio I doubt you'll notice a difference anywhere down the line. Ad a Superchips to the 3.8 and tune for 91 octane and you'll have more torque then the 3.6.

Bottom line is price and longevity, the 3.6 hasn't proved itself yet. And if you want to do mods I guess it really doesn't matter which one you choose.
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Old 12-21-2013, 09:47 AM   #17
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You are correct, as usual.
The 3.6l has a quick torque rise at lower rpms while the 3.8l is more gradual. The largest difference in torque is about 40ft lbs around the 1800 rpm mark. However, the reason why the 3.6l has better crawling characteristics is do to a very flat torque curve from about 1800-3600 rpm. This gives a linear relation between rpm and power output. Makes it feel more predictable and better mannered when crawling. This is noticed when wheels break traction. It's easier to feather the throttle to control wheel speed and slippage.
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Old 12-21-2013, 09:56 AM   #18
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QUick question here. The old/loved/tried and true 4.0 straight six did put out peak torque at really low rpm, but it only mustered 220 lb/ft. The new 3.6 puts out substantially more torque but at higher rpm. Anyone ever seen the torque curve of both engines? Is the new 3.6 really less torquey at 2,000-3,000 rpm? I generally think that a large displacement engine may have the advantage at really low rpm but it is only about 10% larger and used really old technology and think the 3.6 should be able to match it at lower revs.

Based on the 5.0 in my F-150 I can see why a person might think low end torque is really missing because the engine is so much faster when wound up. That can be misleading.

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