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Discussion Starter · #1 ·
I have 35s on a 4 door JK Automatic. I have an intake and exhaust but still feel like I lack the power as well as mpg I should be getting from this.

Almost went with the 4.88s a few months ago but received conflicting information about which way to go vs the standard and the auto. I'm only getting about 12-13 mpg and was getting 16.5 - 19 before the modification. I would like to get both a boost in HP as well as an increase in fuel efficiency. Would a hypertech programmer help as well? I would certainly like to know how fast I'm actually going.

Thanks,
Sam
 

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programmer will for sure get you better, get the gearing and tires working with the computer. Just using my acupro whe I went with 35's made a difference (changes shift points etc).

I went with 5.13's and have no regrets. I have tons of low end omph. I got about 14mpg on a trip 2 weeks ago to Katemcy, that's running 75/80 and around 2700ish rpm. 4.88's would be more fuel efficient but I'm happy with my choice and have zero regrets
 

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Like Bunker said- I believe that 4:88's will yield better mpg, but the 5:13's (especially) with an automatic will give you more "oomph". Most auto guys recommend going to a 5:13, and some say that a 4:88 just wouldn't be that noticeable of an improvement, and therefore- hard to justify.
 

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I've got an auto 4dr with 35's and 5.13's and think it is the only way to go. At 75 mph on the freeway my rpm is just right at 2600. This V6 wants to go down the freeway at above 2500. It behaves much better than it did as a stock Rubi with 32's and 4.10s - 2250 at 75 mph - too low an rpm to keep it in OD and let the cruise work.

Autos with 35's need 5.13's because the trans OD ratio is .69. The stick does fine with 4.88's because the OD ratio is .84.
 

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Let me jump on the b/w as well. I have a 4 door/auto 6" lift and 35's. The thing was a pig on the highway. Now with 5:13 gears I never search for a gear and I can move around and pass people with ease when needed.
 

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513s is the why to go on the auto! i love mine and would not change a thing. My 08 Rubicon is getting them in the spring aswell.
 

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Thanks for all the info on the gears. Looks like the decision will be easy. Now, is the chip worthwhile?

From what I have heard you don't benifit from any real significant gains.
 
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