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Discussion Starter #1
Let me start off by thanking everyone for giving me their opinions on my earlier questions. I just had a 2 1/2" spacer lift installed on my 2013 Rubicon Unlimited, along with Bilstein 5100 shocks and 35" BFG KO2 tires. I originally thought I had 4.10 gears, however it turned out that I have 3.73s. It now seems a little sluggish and my fuel consumption has dropped a couple of miles per gallon. Will it help at all to purchase the Flashpac to reprogram for tire size, speedometer and shifting points? I"m thinking a new gear set is probably what I need, just would rather not spend the money right now. If so, the question is, 4.10 or 4.56. This Jeep is my daily driver, however, I do go off road but not a rock crawler. I'm not sure if the 4.10 is enough lower to feel the difference. On the other hand, I don't want the rpms screaming on the freeway. Thanks for your thoughts.
 

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yes, a Flashpaq will help, try the Tow tune. thats what I used for the last five years. but gears is the best answer...
 

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Let me start off by thanking everyone for giving me their opinions on my earlier questions. I just had a 2 1/2" spacer lift installed on my 2013 Rubicon Unlimited, along with Bilstein 5100 shocks and 35" BFG KO2 tires. I originally thought I had 4.10 gears, however it turned out that I have 3.73s. It now seems a little sluggish and my fuel consumption has dropped a couple of miles per gallon. Will it help at all to purchase the Flashpac to reprogram for tire size, speedometer and shifting points? I"m thinking a new gear set is probably what I need, just would rather not spend the money right now. If so, the question is, 4.10 or 4.56. This Jeep is my daily driver, however, I do go off road but not a rock crawler. I'm not sure if the 4.10 is enough lower to feel the difference. On the other hand, I don't want the rpms screaming on the freeway. Thanks for your thoughts.
The Flashpaq should help; it allows you to really fine tune shifting points (or other items) if you wish, as well as doing simpler general tuning (such as an 87 Octane Tune, which is what I use).
 

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I'd reprogram AND change the gears... both will help.

As for 4.10 vs 4.56, that's a little harder, and also a bit subjective. With those 35s, and presumably automatic tranny, I'd go 4.56.

You have to know that your rig will never be quick, but with the 4.56 it will at least feel peppy (maybe). With he 4.10s, I'd think it would still feel like a dog. Regardless of the type of offloading and driving you do, no one wants a dog for a vehicle. The Pentastar makes decent torque, but to really get all it has to offer, you have to drive higher in the RPMs. The 4.56 will give you more pep lower in the RPM band.
 

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Discussion Starter #8
Just got back in town and checked my thread. Thanks for all of your input. This forum has a wealth of information, because of all of the different experiences it's members are willing to share. I'll start with the Flashpaq, but after driving my jeep for a few days, I'm sure that I will need a gear change, and will probably go with 4.56. Just trying to put the expense off for a while.
 

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Just got back in town and checked my thread. Thanks for all of your input. This forum has a wealth of information, because of all of the different experiences it's members are willing to share. I'll start with the Flashpaq, but after driving my jeep for a few days, I'm sure that I will need a gear change, and will probably go with 4.56. Just trying to put the expense off for a while.
when i finally adjusted for my 35s 5k miles after install it was a huge difference....start with that and report back.....i felt like a had a new faster/smoother jeep.....and i havent even messed with the tunes yet since i have a 15 and it requires a ecu swap. I have 373s also
 

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Discussion Starter #11
Thanks Sneaton. It's good news that it made such a difference. I'm assuming that you used the Flashpaq, is that correct? I will start to do more research, to see where I can get the best price.
 

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Thanks Sneaton. It's good news that it made such a difference. I'm assuming that you used the Flashpaq, is that correct? I will start to do more research, to see where I can get the best price.
yes the flashpaq....but all i was able to use from it was to set the tire size....the other tunes need the ecu swap on the 15s which i havent done. The tunes sound like they would help a lot too from what ive read. Your jeep is really confused right now with the speedo being off. Its really no big deal to try the tire setting first then if youre still unhappy do the regear, you would need the chip to change the ratio anyway
 

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Discussion Starter #13
When doing the tire size change, do you use 35" or 34" which is the actual size of my KO2s?
 

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When doing the tire size change, do you use 35" or 34" which is the actual size of my KO2s?
Use 34" if that's the actual measurement as your jeep sits on the ground. My 315/70r17 duratracs actual measurement is 33.5 and my flashpaq is set to 33.25 for my speedometer to be dead on. Had to play with it a little bit.

How are you calculating your mpg?...just by the digital readout? If so, you're not actually going to gain mpg, you're just making the computer know what's truly going on. Right now your speedometer is off and your odometer is not calculating your mileage for as far as you're actually driving thus your mpg display is reading lower than what you're actually getting in real life. I'm not saying you didn't lose mpg by lifting and adding bigger tires because you most certainly did...just saying that correcting tire size (without adding performance tunes) will make your digital display appear to be getting better mpg but it'll just be the computer working correctly. I'm definitely not an expert by any means but I believe what I have just said to be true...someone please correct me if I'm wrong.
 

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Discussion Starter #15
Back with a report after using my new Flashpaq. Just installed the 87 octane performance program this morning, along with the new tire size for my 35's. It feels like a different jeep. Way more responsive, much better shifting points and my speedometer instead of being off 6mph at 60, is now reading correctly. From my short 30 mile ride on the freeway today, it also seems that my mileage has improved quite a bit, but more on that later. I was right at the point of re gearing, and now I'm not sure that I need to. After some time in 4 wheel drive, I'll make that decision.
 
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