5.38 gears
JK Junkie
Joined: Jul 2009
Posts: 2,343
Likes: 1
From: The San Andreas Fault
Not sure where you got that idea--unless you are looking at the generalized charts that do no match our engine torque/horsepower curve and transmission gearing.
With an automatic and 35s with 5.38s, your rpms are 2495 at 70 mph.
That is perfect for a highway rig with the 3.8L V6 JK engine. Your gas mileage would likely be around 18 at that rpm and your rear wheel horsepower at that rpm should be enough to avoid downshifting on hills and in windy situations.
With a 6 speed and 35s with 5.38s, your rpms would be 3038. That would be a little high. Your gas mileage would probably drop to 14 mpg.
Here is a correct chart:
With an automatic and 35s with 5.38s, your rpms are 2495 at 70 mph.
That is perfect for a highway rig with the 3.8L V6 JK engine. Your gas mileage would likely be around 18 at that rpm and your rear wheel horsepower at that rpm should be enough to avoid downshifting on hills and in windy situations.
With a 6 speed and 35s with 5.38s, your rpms would be 3038. That would be a little high. Your gas mileage would probably drop to 14 mpg.
Here is a correct chart:
I was planning on going to 5.38s but if that right with 40's? I mean I've got 300lbs in bumpers and rails, 100lbs winch, 300lbs tire carrier gas cans and hi-lift. 200lbs stereo. So I'm probably running 1000lbs heavier than stock. So being heavy, stock motor with auto trans and 40in tires. What ratio should I use?
JK Jedi Master
Joined: Jan 2008
Posts: 11,463
Likes: 165
From: Austin <--> Colorado Springs
I was planning on going to 5.38s but if that right with 40's? I mean I've got 300lbs in bumpers and rails, 100lbs winch, 300lbs tire carrier gas cans and hi-lift. 200lbs stereo. So I'm probably running 1000lbs heavier than stock. So being heavy, stock motor with auto trans and 40in tires. What ratio should I use?
JK Enthusiast
Joined: Apr 2008
Posts: 146
Likes: 0
From: Laredo, TX
JK Jedi Master
Joined: Jan 2008
Posts: 11,463
Likes: 165
From: Austin <--> Colorado Springs
There is a place in Houston advertising low cost gearing. Started at $650 parts/labor/out the door. Last I saw, it was up to $850 out the door. Might be worth a drive, depending on how far from Laredo you're willing to go.
Or if you just want the gears, try Northridge. Front and rear gears only for $340. With install kits for $400. With overhaul kits $550.
Or if you just want the gears, try Northridge. Front and rear gears only for $340. With install kits for $400. With overhaul kits $550.
Last edited by nthinuf; Oct 8, 2009 at 02:05 PM.
JK Freak
Joined: Aug 2007
Posts: 618
Likes: 0
From: Manassas, VA
I just went from 4.10's (which i need to sell now I guess) to 5.13's that I got from Northridge. The second i touched the gas, I noticed an immediate diffrence. There was response again... At 60mph, i was turning 1650 RPMs, and it would constantly downshit, i hated driving it on the highway, it just wasnt fun. I had a LONG LONG LONG thought process of going 4.88,5.13, or 5.38's. I runed out 4.88 after driving a friends and didnt think the change was big enough. It then got VERY tough for me to decide between 5.13 and 5.38. Ultimately, i decided 5.13 cause the 5.38 were just to big I thought. I take a major interstate highway to work at 70MPH, then jump on a smaller highway which i run at 60MPH, total of 18miles each way, all highway, and thought the MPG would drop to much.
I have only had my gears a week so far, and honestly, I COULDNT be happier. Hills I struggled with before now cruise right up and I even have some power to spare.... AND I CAN USE CRUISE CONTROL AGAIN.... MPG so far seems pretty decent, i will have better numbers in a few weeks, but really, best Mod I have done for my jeep by far.
I have only had my gears a week so far, and honestly, I COULDNT be happier. Hills I struggled with before now cruise right up and I even have some power to spare.... AND I CAN USE CRUISE CONTROL AGAIN.... MPG so far seems pretty decent, i will have better numbers in a few weeks, but really, best Mod I have done for my jeep by far.