I know there is a search function but I would like to hear from people running this actual set-up on a 4-door with the auto trans. I live in semi-flatland Southern California and have found a nice JK in Oregon with the plan to drive it back here if I decide to go ahead with the deal. I am worried that the gearing may be a little much for a daily driver. I commute close to 35 miles each way 5 days a week, with the hope of dropping it down to about 20 3 days a week. I want the off road ability that this setup will give but don't want to run the engine too hard or have extra crappy gas mileage either with the commuting. What are real world mileage figures for highway driving, I know the JK gets crap mileage but would like the best of both worlds.

thanks

 

I am pretty happy with 5.13's. If you plan on 37's go with 5.38's. You'll be alot happier either or.
My .02 cents.

 

Aside from reduced pinion size, one of the few drawbacks of the 5.38's is that if you drop out of OD while doing 75+ MPH the RPMs fly up above 4K.

 

that sounds like trouble....but will the box do 75+ in a situation where it will drop out of OD?

 

IMO 5.13's were on the edge of being to much for 35's. I cant imagine what 5.38's would be

 

Yeah and if you drop out of OD with 5.13s in the scenario provided you will still be over 4,000 rpm. In fact, there is only going to be a 200 rpm difference after the kickdown and the real key is to prevent the kickdowns from happening in the first place.

The real thief of efficiency and performance is the more immediate and first step the PCM takes when there isn't enough torque provided. That would be the unlocking of the converter and kicking up the rpms about 10%. As you are more reliant on the torque converter, then you have the whole set of issues as to what it means with fluid temperatures along with wear and tear on the transmission.

The whole key is not where your rpms are going to travel on kickdowns but preventing them from happening in the first place. You can much better control torque management via the throttle blade, fuel maps and negative manifold pressure than you can with kicking the responsibility to the transmission and torque converter. You can also do this with very moderate increases in rpm from one gear set to the next steeper set of gears. There isn't anything more than a nominal efficiency loss which is quickly made up for by not unlocking the converter as much.

 

I missed that

I would say your right with the 5.38's and the auto

 

I don't have anything yet. I have found a JK that I am interested in that is already set up with 35's and 5.38's. Just looking for real world info on this set-up. I truly appreciate everyone's help and input on this.

 

Its an auto. Hopefully I can make the deal work.