New jk owner and just got 3" lift with 35" trail grapplers. I expected a drop in mileage... so I'm not really surprised, but I didn't expect to go from 16.4 mpg down to 12.5 and be so sluggish. Now trying to decide whether to re-gear from 3.73's to 4.88's. Or to first try superchips and maybe performance exhaust or air intake. Trying to watch the budget so can't do it all, but would like some pro's and con's that might help me improve the performance. Thanks!

 

You need to get your speedo right so your transmission shifts properly, but that isn't going to take care of the lack of appropriate gears. 5.13s or better for 35s. As for the rest of the intakes and exhausts all of them in total aren't going to even get you close to half of what the gears will.

 

You will probably get both eventually. As JPop pointed out the superchips flashpaq allows you to adjust the computer for your tire size and gear ratio. If money is tight I'd probably do the superchips flashpaq first just because it's a lot cheaper than getting gears installed. Then when you do have the cash for the gears you'll be able to set your gear size appropriately with the flashpaq.

Gears are going to make the biggest difference, but without being able to tell the computer what size tires and what your new final drive ratio is I'm not sure how well your transmission will behave.

 

We basically have the same vehicle (Unlimited, Auto, BD 3" suspension, 35" tires). I finally, after 6 months, did the Flashpaq and 5.13 gears. I wish I had done it sooner because I would have already had a 50 percent return on my investment from fuel savings alone. I saw my MPG increase from 13 to 16 on average, and actually see 18MPG on the highway at 70ish MPH.

The Flashpaq is a no-brainer. Get one immediately. If you're considering an intake and exhaust, then spend the extra $400 or so and get the gears done as well. You'll be glad you did.

You asked for pros and cons.

Pros:

1. Better fuel economy
2. The transmission will no longer hunt for gears at freeway speeds or on inclines
3. Improved throttle response (some say too good)
4. Control over other functions such as TPM settings, fuel type, etc.
5. You'll be able to merge with traffic and/or pass people on the freeway! Seriously, the difference in power is very evident.
6. GUARANTEED return on investment. I'd say 100 percent in 18 months.

Cons:

1. It costs money. Well, whatever.
2. The higher gear ratio means the gears themselves will actually be weaker. This is a bigger deal if you have a Dana30 up front.
3. If you have a Dana30 up front and plan to do lots of hard wheeling and/or run 37's, then you'll eventually want to upgrade to at least Dana44 up front ... which means buying/installing gears on that axle again.
4. Your drive shafts will be spinning much faster (about 38 percent) at any given road speed, which can exaccerbate existing issues with driveshaft balance or high pinion angle.
5. Your top speed will decrease (but seriously, why would you want to take it over 95MPH anyway?).

Can't think of too many other cons, really. It might seem like a lot of money up front, but I guarantee you will save money over time. The difference in fuel economy is that significant.

Good luck with your decision.

-Dawn

 

Thanks all SO much for the advice. These are some difficult decisions when I really am TOTALLY ignorant of anything automotive! I definitely feel more comfortable about re-gearing - although the shop I deal with recommended I go with 4:88's. I'm especially eager to get this done after driving on the interstate today and feeling like I couldn't even get it to go the speed limit. Love, love, love my jeep. And don't care that it's not a speed demon. But...I at least need to feel capable of merging into traffic.

 

I think you have to consider who is more qualified to recommend the correct gear ratio. Is it the shop that says 488s or the many JK owners that are running 35s and 513s. Who has the most real world experience. I'm getting ready to do the same route and all of the 5 offroad shops I called, recommend 513s, but my Rubi has 44s F&R. If you have 373s now, you must have a d30. 513s will get you a pretty small pinion. In that regard, maybe 488s will give you a little more strength.