Yugo Engine In My JK.
12-04-2007, 11:43 AM
#21
JK Freak
Hey Fishit, I live here in Utah and have a 2 DR Sahara. When mine was stock I could get 19-20 mpg. Then with the lift and 35" tires It lost all of its power. I regeared to 4:88's and the power is much better. My computer is not accurate but is showing 12.8-13.5 I tend to drive it hard and really havent watched milage very close. Dotn they recomend 87 octain? The regear will definately help with power. I had mine done at six states. About $1,000. total. good luck,
lets go wheelin or fishin or both
lets go wheelin or fishin or both
12-04-2007, 11:46 AM
#22
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Hey Fishit, I live here in Utah and have a 2 DR Sahara. When mine was stock I could get 19-20 mpg. Then with the lift and 35" tires It lost all of its power. I regeared to 4:88's and the power is much better. My computer is not accurate but is showing 12.8-13.5 I tend to drive it hard and really havent watched milage very close. Dotn they recomend 87 octain? The regear will definately help with power. I had mine done at six states. About $1,000. total. good luck,
lets go wheelin or fishin or both
lets go wheelin or fishin or both
12-04-2007, 11:48 AM
#23
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another question about regearing. My main coplaint about lack of power is when I am in the top gears, when I am on the freeway and need to merge into a faster lane, I hit the gas and barely speed up. In other words when I am driving 55 and need to gas it to 65 I get nothing. Will regearing give me more power there or is mostly in first and second gear?
12-04-2007, 11:57 AM
#24
JK Freak
It should cost about the same minimal difference at most. Regearing will change the power in all gears. I still need to lock out the OD on steep climbs.
(Traverse mountain, Parleys, or trying to drive it like my Porsche)
(Traverse mountain, Parleys, or trying to drive it like my Porsche)
12-04-2007, 12:12 PM
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what do you mean lock out the OD? I actually live half way up traverse ridge road so I am reminded every day how sluggish this thing is. Thanks for all the info.
12-04-2007, 12:39 PM
#26
On hills, just turn off your overdrive, that will help as well as be a little easier on your transmission.
12-04-2007, 12:44 PM
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It's the same...Most recommend 5.13's with an auto and 35's. If you are going to stay with 33's 4.88 will be a good match. But remember 33's now might turn into 35's down the road. It's hard to not want more once you get used to what you have. You have to know yourself, and what your future holds. 33's with 410's isn't that bad though.
On hills, just turn off your overdrive, that will help as well as be a little easier on your transmission.
On hills, just turn off your overdrive, that will help as well as be a little easier on your transmission.
12-04-2007, 01:01 PM
#28
$1000-$1200, make sure you go to a reputable place...Get a referral in your area. If you are eyeballing 35's go with the 5.13's. I haven't done mine yet due to finances, but that's what I will do. It seems to be the consensus here for autos. People say it feels like you added a bunch of horse power. Read through some regearing threads here, there are a lot of them, just so you can be informed when you make your decission.
12-04-2007, 01:37 PM
#29
First of all, I apologize for the extremely long post and agree that it seems like re-gearing is the best way to go here. But I have to disagree with the OP's opinion about the power vs. economy of the JK. On another forum, I put together the following really long post that consolidates my various responses over the past year or so regarding the 3.8 power/economy complaints. A lot of this references a comparison to the TJ with the 4.0, which most seem to feel is adequate power wise, but I think it applies here. Again sorry for the book - you may want to skip if you fear eyeglazeoveritis!
When you compare the torque curves of the 3.8 and the 4.0 there is not much difference. Yes, the 3.8 torque peak comes at a higher rpm but it doesn't just drop off before the peak - the 3.8 is still an OHV, relatively torquey engine. While I agree that the TJ's 4.0 is a slightly more torquey engine (I had a XJ w/the 4.0 for a while so I'm familiar with it), I think a bigger difference between the drive feel of the TJ and JK is the gas pedal recalibration. A lot of TJ owners, particularly rock climbers, have complained over the years that the TJ gas pedal was too touchy - making it more difficult to negotiate slow, technical terrain. I am not a former TJ owner, but I've driven TJs offroad enough to agree with this complaint. You get used to it, but I always thought a true rock crawler should have a nice smooth/slow throttle. I think the JK throttle control is great - if you want it to go fast you've just got to lay into it quite a bit, which many people are not used to, particularly former TJ/XJ owners. Anyways, just goes to show you can't please everybody.
Also, the TJ is not a fast vehicle, but it does feel fairly fast, especially around town because it rides rough and is noisy. It is a visceral experience. Kind of like when I used to drive around in my buddy's Willys on the freeway. We were going 55 but it felt like 100. The JK is a little more refined to drive, so you don't get the same feel.
As for the 3.8 in general, I disagree with the OP. I've driven the 2-dr and I think the 3.8 is perfect for it. Power to weight ratios generally tell a pretty good picture about the feel of a vehicle. I did a quick comparison and the ratio of a 06 Rubi (swb) is 19.7. The ratio of a 07 Rubi (2-dr) is 20.4. So each JK horse is pulling a little more than an additional half pound. That is really a very small increase, but it will likely make the JK feel a little more sluggish than the TJ. Add the change in experience due to the raw nature of the TJ and the fact that most everyone has been driving and posting their experiences with the JK 4-dr (which is even heavier than the 06 Unlimited) hence the opinions that the JK is underpowered. Here is how the power to weight ratios of the Unlimiteds compare: 06 - 20.5, 07 - 21.4. Thus, the 2-dr JK should feel a lot like the 06 Unlimited in terms of quickness. The 4-dr. should feel a bit slower. To put all of this into perspective - the power to weight ratio of a 1942 Willys Jeep - 45.4 lb/hp.
I have a JK Unlimited Rubi Auto and I do think that it is slightly underpowered with the 3.8, but I think it is perfect for the Jeep and wouldn't upgrade unless it were a no cost option. It is relatively fuel efficient, it is an older, proven technology that is apparently easy to work on, and it is relatively torquey. I also agree that the engine (or computer program) loosened up considerably after 3-4,000 miles. It's still slightly underpowered, though - not much acceleration or passing power. For a car, that would be a major issue for me. For a Jeep, however, dependability, simplicity (for quick trail fixes), fuel economy (for long trail rides), and torque (for rock crawling and mud running) are much more important to me.
As for fuel economy, the JK is great for what it is in my opinion - the JK is not a minivan or a Dodge Stratus, it is a 4x4 convertible vehicle that is shaped like a brick with heavy duty running gear. When you compare the actual mpg numbers of similar vehicles, the JK is actually pretty fuel efficient:
07 JK 4x4 Auto - 16/19 (city/hwy)
07 JK 4x4 Manual - 17/19
07 JK 4x2 Auto - 17/21
07 JK 4x2 Manual - 18/22
07 FJ Cruiser 4x4 Auto - 17/21
07 FJ Cruiser 4x4 Manual - 16/19
07 FJ Cruiser 4x2 Auto - 19/22
07 H3 4x4 Auto - 15/19
07 H3 4x4 Manual - 15/20
04 Dodge Caravan AWD Auto - 15/21
As you can see the JK holds its own in actual mpg comparisons. Yes the FJ has a more powerful engine with similar economy, but it is also slightly more aerodynamic, has less robust running gear, and comes with a more efficient 5 spd auto for the auto version. The tradeoff is the FJ engine is arguably more difficult to work on than the JK engine and requires premium fuel. Note the H3 numbers - similar numbers for similarly poor aerodynamics and strong running gear, but the H3 has a 5-cylinder engine and still can't beat the JK's numbers. I included the 04 Caravan, because that's the last year Dodge offered it in AWD and it has essentially the same engine as the JK. Note that the JK actually gets better mpg in the city and is not far behind on the highway.
The frustrating thing to me in reading a lot of the negative posts is that if Jeep really wanted to get an extra few mpg with the 3.8 they could have improved the aerodynamics further (more slanted windshield, no fender gaps, spare under vehicle, dropped various underbody components to improve airflow under the vehicle, dropped the vehicle to minimize underbody airflow, smaller mirrors, etc.) or they could have made the drivetrain more efficient (smaller, more efficient axles; 5 spd. auto). With the possible exception of a 5 spd auto (which probably was not added for cost reasons - I could see that being added later, possibly in combo with a new engine option) Jeep did not make these changes because they wanted to increase the trail-worthiness of the Jeep as a first priority with increased fuel economy as a lower priority. We should be praising Jeep for keeping the Wrangler styling cues intact and making the drivetrain more robust for off-road conditions (which is what everyone on the forums was asking Jeep to do, by the way) instead of designing the JK for maximum fuel economy. Jeep did do some things, by the way, to increase fuel economy and has been berated for them in the forums, almost without exception (how many people on the forums praise Jeep for curving the windshield or installing the plastic air dam). Again, you can't please everybody. Sure Jeep could of improved the mileage by making the vehicle more aerodynamic and weakening the mechanicals, but I'm glad they didn't. They are offering a 2WD option, which improves mpg (and again, they were berated by many for even offering such an option). If mpg is a prime consideration get the 2WD.
When you compare the torque curves of the 3.8 and the 4.0 there is not much difference. Yes, the 3.8 torque peak comes at a higher rpm but it doesn't just drop off before the peak - the 3.8 is still an OHV, relatively torquey engine. While I agree that the TJ's 4.0 is a slightly more torquey engine (I had a XJ w/the 4.0 for a while so I'm familiar with it), I think a bigger difference between the drive feel of the TJ and JK is the gas pedal recalibration. A lot of TJ owners, particularly rock climbers, have complained over the years that the TJ gas pedal was too touchy - making it more difficult to negotiate slow, technical terrain. I am not a former TJ owner, but I've driven TJs offroad enough to agree with this complaint. You get used to it, but I always thought a true rock crawler should have a nice smooth/slow throttle. I think the JK throttle control is great - if you want it to go fast you've just got to lay into it quite a bit, which many people are not used to, particularly former TJ/XJ owners. Anyways, just goes to show you can't please everybody.
Also, the TJ is not a fast vehicle, but it does feel fairly fast, especially around town because it rides rough and is noisy. It is a visceral experience. Kind of like when I used to drive around in my buddy's Willys on the freeway. We were going 55 but it felt like 100. The JK is a little more refined to drive, so you don't get the same feel.
As for the 3.8 in general, I disagree with the OP. I've driven the 2-dr and I think the 3.8 is perfect for it. Power to weight ratios generally tell a pretty good picture about the feel of a vehicle. I did a quick comparison and the ratio of a 06 Rubi (swb) is 19.7. The ratio of a 07 Rubi (2-dr) is 20.4. So each JK horse is pulling a little more than an additional half pound. That is really a very small increase, but it will likely make the JK feel a little more sluggish than the TJ. Add the change in experience due to the raw nature of the TJ and the fact that most everyone has been driving and posting their experiences with the JK 4-dr (which is even heavier than the 06 Unlimited) hence the opinions that the JK is underpowered. Here is how the power to weight ratios of the Unlimiteds compare: 06 - 20.5, 07 - 21.4. Thus, the 2-dr JK should feel a lot like the 06 Unlimited in terms of quickness. The 4-dr. should feel a bit slower. To put all of this into perspective - the power to weight ratio of a 1942 Willys Jeep - 45.4 lb/hp.
I have a JK Unlimited Rubi Auto and I do think that it is slightly underpowered with the 3.8, but I think it is perfect for the Jeep and wouldn't upgrade unless it were a no cost option. It is relatively fuel efficient, it is an older, proven technology that is apparently easy to work on, and it is relatively torquey. I also agree that the engine (or computer program) loosened up considerably after 3-4,000 miles. It's still slightly underpowered, though - not much acceleration or passing power. For a car, that would be a major issue for me. For a Jeep, however, dependability, simplicity (for quick trail fixes), fuel economy (for long trail rides), and torque (for rock crawling and mud running) are much more important to me.
As for fuel economy, the JK is great for what it is in my opinion - the JK is not a minivan or a Dodge Stratus, it is a 4x4 convertible vehicle that is shaped like a brick with heavy duty running gear. When you compare the actual mpg numbers of similar vehicles, the JK is actually pretty fuel efficient:
07 JK 4x4 Auto - 16/19 (city/hwy)
07 JK 4x4 Manual - 17/19
07 JK 4x2 Auto - 17/21
07 JK 4x2 Manual - 18/22
07 FJ Cruiser 4x4 Auto - 17/21
07 FJ Cruiser 4x4 Manual - 16/19
07 FJ Cruiser 4x2 Auto - 19/22
07 H3 4x4 Auto - 15/19
07 H3 4x4 Manual - 15/20
04 Dodge Caravan AWD Auto - 15/21
As you can see the JK holds its own in actual mpg comparisons. Yes the FJ has a more powerful engine with similar economy, but it is also slightly more aerodynamic, has less robust running gear, and comes with a more efficient 5 spd auto for the auto version. The tradeoff is the FJ engine is arguably more difficult to work on than the JK engine and requires premium fuel. Note the H3 numbers - similar numbers for similarly poor aerodynamics and strong running gear, but the H3 has a 5-cylinder engine and still can't beat the JK's numbers. I included the 04 Caravan, because that's the last year Dodge offered it in AWD and it has essentially the same engine as the JK. Note that the JK actually gets better mpg in the city and is not far behind on the highway.
The frustrating thing to me in reading a lot of the negative posts is that if Jeep really wanted to get an extra few mpg with the 3.8 they could have improved the aerodynamics further (more slanted windshield, no fender gaps, spare under vehicle, dropped various underbody components to improve airflow under the vehicle, dropped the vehicle to minimize underbody airflow, smaller mirrors, etc.) or they could have made the drivetrain more efficient (smaller, more efficient axles; 5 spd. auto). With the possible exception of a 5 spd auto (which probably was not added for cost reasons - I could see that being added later, possibly in combo with a new engine option) Jeep did not make these changes because they wanted to increase the trail-worthiness of the Jeep as a first priority with increased fuel economy as a lower priority. We should be praising Jeep for keeping the Wrangler styling cues intact and making the drivetrain more robust for off-road conditions (which is what everyone on the forums was asking Jeep to do, by the way) instead of designing the JK for maximum fuel economy. Jeep did do some things, by the way, to increase fuel economy and has been berated for them in the forums, almost without exception (how many people on the forums praise Jeep for curving the windshield or installing the plastic air dam). Again, you can't please everybody. Sure Jeep could of improved the mileage by making the vehicle more aerodynamic and weakening the mechanicals, but I'm glad they didn't. They are offering a 2WD option, which improves mpg (and again, they were berated by many for even offering such an option). If mpg is a prime consideration get the 2WD.
12-04-2007, 01:55 PM
#30
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That was an excellent read. Thanks. I found much of what you posted very valuable. I think I am going to regear and be thankful that the jk still looks and rides like a jeep which is the most important part for me. I have been driving expensive and fast company cars for the last 5 years and now I'm just trying to get used to not driving in the fast lane. I have been getting the hang of the far right lane over the last month. Its actually a lot more peaceful over there.