Preparing to re-gear. Anyone with this set up?

[FLGeezer]

So, using the tape on the tire/tape on the driveshaft method, it looks like I have a 3.21. I wasn't sure because the tags are missing on the diffs. PO said it has a "3.8" axle ratio when I asked but I think he thought I was asking about the engine (it's a 3.8L) but then I wondered if he meant 3.73.

Anyway, mine is a 3.8L, 6-speed manual with 35s. And contrary to the chart and what people say, it's not sluggish at all. In fact, it's quicker than a jackrabbit. It does take for-bloody-ever to reach 70mph though. I live on a barrier island and don't get over to the Interstate often and the one time I did I wasn't paying attention to the RPMs. I may do that this weekend.

 

[Dirty Dog]

So, using the tape on the tire/tape on the driveshaft method, it looks like I have a 3.21. I wasn't sure because the tags are missing on the diffs. PO said it has a "3.8" axle ratio when I asked but I think he thought I was asking about the engine (it's a 3.8L) but then I wondered if he meant 3.73.

Anyway, mine is a 3.8L, 6-speed manual with 35s. And contrary to the chart and what people say, it's not sluggish at all. In fact, it's quicker than a jackrabbit. It does take for-bloody-ever to reach 70mph though. I live on a barrier island and don't get over to the Interstate often and the one time I did I wasn't paying attention to the RPMs. I may do that this weekend.

You live at sea level, in an area where a 2 degree incline is steep. And you're a self-described geezer. All of which affects the subjective statement that it is "quicker than a jackrabbit". Go do a measured quarter mile run and post the ET and trap speed. I'm betting your statement is... optimistic...

For reference, the stock 3.8L JK 2-door is a 16.1 second car, at sea level, with a professional driver. The 3.6L is a 15.3 second car, under the same conditions. I don't think you will find many people who think either of those is "quicker than a jackrabbit", and it's a sure thing yours is slower.

Your time to beat is my car. At sea level, it runs 10.9 seconds, but that's with me driving, on low-profile street tires, without even lowering the tire pressure. On pump gas. With the stereo playing and the AC on. You're more likely to find agreement that that is "quicker than a jackrabbit".

 

[FLGeezer]

Yep, the steepest incline for me is the bridges over to the mainland. But, I have an F150 with a V8 and it's not as peppy as the Jeep. 'Course now you'll reply with "ackshually, the Jeep is lighter....."

Go do a measured quarter mile time and post the ET and trap speed.

I already said it took forever to reach 70mph. But, around town it's zippy as heck. The chart says sluggish performance...at minimal elevation, and it's not. Not at all.

 

[MacGuyver]

The 3.8, while not fast, is mostly hated (I think anyway) because of that damn Auto they paired with it. If you have a manual, it's fine. A bit oil burny, but it goes down the road and does highway stuff and dirt stuff just fine.

I imagine a two door and manual is just as fun as my 99 TJ.

 

[Dirty Dog]

The 3.8, while not fast, is mostly hated (I think anyway) because of that damn Auto they paired with it. If you have a manual, it's fine. A bit oil burny, but it goes down the road and does highway stuff and dirt stuff just fine.

I imagine a two door and manual is just as fun as my 99 TJ.

The automatic certainly doesn't help.

But bottom line is that it just doesn't produce enough HP or torque for a 4,000+ pound vehicle that's shaped like a shoe box. If you look at the dyno chart below, you can see that the 3.8 is WAY under the 3.6 (which is not exactly a beast of an engine either) throughout the entire power band. Especially in the 1500-3200 range, where you spend the vast majority of your time driving. And also at the upper end, when you're really mashing the loud pedal. The only place it's even close (though still lagging) is in the 3300-4300 range. A range you'll not be spending any significant amount of time in.

Flat torque curves are The Bomb Diggity.

 

[FLGeezer]

.

 

[Dirty Dog]

So I just got back from taking it out on the highway and I must have been driving a different Jeep the one other time I drove on the highway. Today it got up to 70 (and 80) just fine. No problem. Perhaps there was a headwind the first time.

Or maybe you have a really soft idea of what "zippy" means?

Now, here's what's interesting: at 70mph in 5th I was seeing a little over 2100 RPMs.

Why were you in 5th at 70MPH? Don't have enough power to use 6th? In any case, there's no point in comparing your RPM in 5th gear to a chart showing RPM in 6th...

 

[FLGeezer]

.

 

[Dirty Dog]

Where does it say 6th?

Why would they make a chart using anything other than the highest gear available? After all, that IS kind of the point of the chart...
And you DO see where it says "OD use", right? 5th gear is not OD. It's 1.00:1. So...

The fact that you find yourself unable to use OD at 70MPH, at sea level, on flat ground, indicates that the chart is quite accurate.

 

[SteveF]

I have a 2015 with 35's. I use my jeep about the same as the OP. The build sheet said I had 3.73 gears. But it actually had 3.21. It would downshift alot on the highway at the slightest incline. I re-geared to 4.56 gears and couldn't be happier.

 

[MacGuyver]

The automatic certainly doesn't help.

But bottom line is that it just doesn't produce enough HP or torque for a 4,000+ pound vehicle that's shaped like a shoe box. If you look at the dyno chart below, you can see that the 3.8 is WAY under the 3.6 (which is not exactly a beast of an engine either) throughout the entire power band. Especially in the 1500-3200 range, where you spend the vast majority of your time driving. And also at the upper end, when you're really mashing the loud pedal. The only place it's even close (though still lagging) is in the 3300-4300 range. A range you'll not be spending any significant amount of time in.

Flat torque curves are The Bomb Diggity.

lol, I was specific in my use of the word 'fine'. It's not amazing, but it does the job. I certainly would rather have the 3.6. Though the 3.8 is much easier to work on.