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JK LS conversion real time fuel economy

25K views 21 replies 8 participants last post by  swab 
#1 ·
Hey all, long time lurker, first time poster so hey to everyone!

Im here in Aus with a 2010 JKU sporting the p.o.s 3.8l that is on its last breath.
So I have been doing ALLOT of research into converting to a 6.0l L76 with the 6 speed trans, which are very common here in our Holden Commodores.

Do any of you guys or gals have a accurate MPG reading with a LS swap into your JK's?

Cheers!
Paul
 
#2 ·
If you do a Google search for your combination you will find a lot of stuff on this subject. That's a larger mod than most people on this particular forum would have experience with. Add the word motown to that search. The guy who owns that company has done a lot of write ups on his ls swaps.

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#5 ·
From what I have read the gm combo can get good mpgs when driven for it. One thing to consider that 6 speed auto has much better gearing. Also the larger engine will not go in to power enrichment as quickly since it's not laboring the same on the hwy

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#7 ·
Thanks!

LS 6.0 with GM 6l80 transmission, 4.10 gearing on moderately heavy JKU. I average 16.5 mpg mixed highway and city driving. Motech did my swap, have had it for around 5 months. The difference in drivability vs the 3.8 is significant, now the Jeep actually has power.
Gee that's not to bad at all, so basically 3.8l fuel economy with the v8 power? What MPG does it actually go down to say cruising on the hwy at 65mph?
The reason for concern is that petrol is around $5 a gallon here ($1.30 per litre) and we have diesel models her that average 19mpg, but I want a V8!
 
#8 ·
Stop and go traffic hurts mileage more than highway driving. I've done a couple road trips where I'm averaging 80mph and mileage was essentially the same. With 35" tires and 4.10 gearing I'm around 2100 rpm at 80mph. This is where the engine likes to be so its not lugging and not over revving trying to make power. The 6 speed tranny is so much better as well. Highway driving at 65mph will give you good fuel economy.
 
#9 ·
If you the get the L76, get the DOD feature removed from the tune, or better, get the DOD removed from the engine with a DOD delete, then shut it off in the calibration, depending on the year, like earlier 09's, they had weak DOD lifters, the revised lifters were a lot better, but DOD in a Jeep will suck even more than what it does in a car, works great in flat areas if you cruising down the fwy at a constant speed, but using 4 cyl everywhere else, especially in hilly areas and city for the most part, would make you use more gas rather than less, plus if you get an exhaust, it'll sound like a complete turd when those 4 cyl are engaged.
 
#15 ·
Not sure of what "DOD" stands for but, if it is what I think it is, in our truck, an '11 GMC Sierra 1500 4x4 with the 5.3, it's called Cylinder Deactivation. And, you state that having it operate in hills etc, would suck. Well, on ours, it won't even think of turning on, unless the truck is on perfectly flat, level freeway, and is using the cruise control and, has been at a constant speed for a given amount of time. Then, and only then, will I see it on the dash that it is activated.
We've had the truck now for several years and, have driven it in every type of scenario and, as stated, it only activates in nothing less than perfect cruising freeway conditions.
Scott

Oh, By the way, yes, it has the Allison 6 speed auto.
Scott
 
#10 ·
#11 ·
Hey Gang,
Wow, I had no idea there are so many doing the conversion to the 5.3 and the 6.2. That's great. Just wondering a few questions.

1. I was told a long time ago that, if you went to say, a Grand Cherokee motor, like the 5.7L Hemi, that most if not all the gauges etc. would work due to using the same manufacturer.

2. But, using say, a 5.3L GM motor would cause all kinds of havoc on trying to make all the stock gauges, lights, icons etc. work due to its a GM going into a Chrysler/Jeep product.

3. How about any vibrations at freeway speeds due to shortening the total length of the drive train, due to the use of adapters which normally would not be there?

This is real interesting to me. ]
Scott
 
#12 ·
No drivetrain issues at all, Im using the same driveshafts before and after the swap so no significant change in length. Motech and other swaps integrate a GM computer which controls engine/transmission functions with the Chrysler computer which handles other things like the gauges so everything works and looks factory. JKowners forum has the most information I've seen about swaps. Lots of user experience and also a presence from Motech and others like RPMExtreme.
 
#17 ·
DOD stands for Displacement on Demand, term wildly used in the G8GT community, and yes, it encompases the cylinder deactivation feature, most GM 5.3L use the technology, my 2010 Silverado 5.3L has it, though i did disable it in the tune 2nd day of ownership.

2009 Pontiac G8 GT - High Performance Pontiac Magazine

If you want to remove the DOD physically, the aftermarket have kits available for the L76, or any 5.3L engine from GM
https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=dod delete kit
 
#18 ·
DOD stands for Displacement on Demand, term wildly used in the G8GT community, and yes, it encompases the cylinder deactivation feature, most GM 5.3L use the technology, my 2010 Silverado 5.3L has it, though i did disable it in the tune 2nd day of ownership.

2009 Pontiac G8 GT - High Performance Pontiac Magazine

If you want to remove the DOD physically, the aftermarket have kits available for the L76, or any 5.3L engine from GM
https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=dod delete kit
This may be a really dumb question but, why would you want to disable it? Like I stated earlier, mine, in my truck, will only work when all kinds of parameters are met. It has never activated in any other driving condition or, set of parameters, than what I've described and therefore, has never hindered any of the trucks performance. In our truck, if it's active, and we encounter a grade or, rise of any type in the freeway (only condition it will operate on) it will self disengage and, the engine goes back to all eight cylinders operating.
Scott
 
#20 ·
I must be missing something here, again. You stated the Jeep experiences more loads due to aerodynamics, correct? Well to me, that would simply mean that, based on the way that Cylinder Deactivation is designed to operate, if NO LOADS are detected and, the engine and trans are in sync and, the speed is constant, then, and only then, would the cylinder deactivation engage.

But, if ANY LOADS should be encountered, such as what you say Jeep experiences, due to aerodynamics, then in my opinion, the cylinder deactivation will NEVER engage, correct? So, then why would there be a need to disconnect it. Just trying to learn here.
Scott
 
#21 ·
Check out why its recommended to delete the DOD system on the LS forums. Many issues with the lifters esp the earlier systems.
 
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