I have a 2011 3.8L 2dr 6pd with the stock 3.21 gears. It is quite unbearable on the highways and in the mountains of upstate New York. I am planning to regear, but am torn between 4.1 and 4.56 ratios. I have read through countless threads and taken a look at the recommended gearing chart for the 3.8L. The charts seem to recommend 4.1 for a daily driver, but many threads seem to suggest going for the 4.56s. I rarely off-road. I am currently running 285/70/r17s and do not plan on going larger than 33s. Would 4.56s run too high on the highway at 70-75mph? Are 4.1s sufficient for a daily driver?

 

That 3.8L could use all the help you're willing to throw at it. Even if you go to a 33" tire, that will likely measure more like 31.5-32" once under the jeep and inflated to your desire. With 3.8L manual, 4.56 puts you in that 2600-2700 rpm range @ 70mph. IMO, that is the target for most folks. I'm sure you'd get by with 4.10s, the question would be if you will wish you had gone lower. Whatever you go with, don't expect it to feel like you added a supercharger .

 

Thanks for the guidance! I certainly don't expect supercharger performance. I just want to be in a more appropriate RPM range to avoid constant downshifting on the highway. Care to elaborate on how you ended up with 2600-2700RPM @ 70mph? According most calculators and charts I've seen, it would be more like 2800RPM and in the "performance" zone, while 4.1 puts me at ~2500RPM.

 

I'm sorry, you are correct. Last night I searched specifically for the 3.8L chart, scrolled right to manual and totally overlooked that I was on 3.6L instead and needed to keep scrolling. Mentally I knew I had searched for 3.8L.

I've never owned a 3.8L, but have always had the understanding it is more accommodating to higher rpms than the 3.6L. That range is where I live with my 3.6L so I'm used to it. Given you live in/around mountainy areas, you might appreciate that more. How much fast driving, at 75 mph or more do you do? Daily driving typically isn't where those higher rpms get ya as much as say 3-5hr road trips where you might be cruising at 75-80mph. I will say though that you manual guys have an easier time with things cuz you don't have that auto tranny constantly searching around for gears if the person in the car in front of you farts. Just about every gearing decision comes down to "they'll both work just fine" and it then just depends on which way you want to lean based on your driving habits and geographic location. I could tell you not to be scared of ~2800 rpms. You can obviously see what that feels like cruising around on the highway by driving in a lower gear. Reaction times will be a little different with lower gear obviously, but it's the engine sound to pay attention to.

 

I can only speak from my experience, I have 4.88's and 35's with an Auto. I am good and don't feel the need to re-gear, but if I did it again, I'd run with 5.13's.

My advice is to go a bit higher than you think you need.

 

Ive got 4.88s with my 3.8, 6 speed. i was running 35s now 37s. the 4.88s worked wonders with my 35s and are still in a good range with the 37s

 

Go with the 4.56s IMO. I had a 3.8 on 33s and steelies with stock gears, I understand how terrible it is. Mountain roads especially, I'm sure you're in 3rd and 4th just to stay above 50. The taller ratio will make up for the lack of power and torque.

 

08 JK here, with the 3.8l and 6 spd manual. Because of the altitude where I live (6,000 feet), I'm down about 20% in power and need all the help gearing can give me. With 285/70-17 tires I'm running 4.88:1 gears. They are great everywhere EXCEPT higher speed cruising as I'm not comfortable with engine speeds over 3,000 rpm for long periods of time. That's the only downside to steeper gearing. My gas mileage is still acceptable at 17 +/- MPG.

To the OP: Go 4.56 or higher. That'll make your slug at least acceptable in the mountains.

 

4.10's will get the job done with the 6 speed. 4.56 will allow you to go slightly bigger on tires in the future. Even though you say never bigger, jeepers tend to go bigger over time.

 

My 2011 3.8l 6spd came with 3.21 gears. even with the stock tires, 6th gear was practically useless, then I put a lift and tires on it and wow... I could cruise at 80mph in 4th gear without breaking a sweat, it was ridiculous and stupid. Just had the 4.56 yukon gears installed and WOW! what a night and day difference.... it's incredible actually. I can now use 6th gear in cruise control & actually maintain my speed and i no longer lose speed going up hills. 4high is now very much usable, averaging about 17mpg, it is overall much more fun to drive now really wakes the 3.8 up