jtphoto JK

Own 3 with 3.8 and drive one or the other everyday for the last 9 years. I also drive the 3.6 every other day or so both Modded and Unmodded.

lloydsmale

all I know is I owned a 3.8 auto rubicon with 410s and 32 inch tires and this willys with an auto 373 geared with 34 inch tires and the 3.6 will walk circles around the 3.8. Has as much or more low end grunt and gets about 4mpg better fuel economy (well it did when they both had 32s). Well it got 4mpg better before I put the 34s on it. Lost a couple mpg with the 34s. I'm not saying its a sports car in comparison as I think even the 3.6 lacks in low end torque. But given a choice id take a 3.6 anyday over a 3.8 even if the oil consumption problem didn't exist.. By the way my 3.8 rubicon used maybe quart of oil every 5k which I consider nothing. The 2015 silverado I just traded on the new truck did that from new.

jtphoto JK

I am sure it does feel that way. That would be like comparing a 3.6/3.21 to 3.6/4.10 combination. Due to poor gearing with the 3.8s 4spd auto you'd have to run 4.56 to even come close to compare to the 3.6 with 3.73 combination. Check out the gearing charts and you'll see what I mean. It's the common misconception, but it's not the motor that makes it feel like a dog it's the high geared transmissions (6spd included). Mileage I think is too driver specific and too dependent on so many factors. I can get 18-19mpg with my rig (3.8 auto, 5.38, 37" Pitbulls) on the highway at 60mpg. Push it faster and mpg drops fast. My average is usually 16-17mpg mixed ....

jtphoto JK

Just as a point of interest.

3.8 auto with 5.38 and 37" tires 2,300rpm at 70mph

3.6 auto with 5.38 and 37" tires 3,002rpm at 70mph

Take it the other way now.

3.8 auto with 3.73 and 32" tires 1,892rpm at 70mph at 50-55 that drops under 1,400rpm

3.6 auto with 3.73 and 32" tires 2,276rpm at 70mph.

For me cruising at 60mph is around 2,100rpm. Which is the sweet spot.

silverbullet88

I can't even hold 3rd gear at 2950ish up hills at 65mph. 60 if I'm lucky. 4.10's. 35's. 3.8

zstairlessone

Something is wrong, At 2900 RPM I can not only hold 6th up a hill but can accelerate, if I drop to around 2600-2700 I have to put it in 5th to maintain or accelerate up steep hills. I too have 4.10s, a 3.8 and my tires physically measure just under 34" at the shoulder (measure your 35s to see how tall they really are).

Also, 3rd gear with a 6-speed and 4.10 gears at 2950 RPM and 65 mph?? I'm going to have to check that out today, doesn't seem close to me, GPS speed of 80 MPH (indicated 74) in 6th gear and 2900 RPM is what I see, and yes we have an 80 MPH stretch of I-10 in Texas and it has some pretty steep hills.

silverbullet88

The problem is my auto transmission! My tires only measure 33.25 ish.

Maybe something is wrong? Haha

jchappies

The difference is definitely in the gearing.
The 3.6 has a 3.59 1st gear compared to the 3.8 with a 2.84 1st. Your going to feel like you have more power at take-off

Since I added the RIPP and 5.38 gears the Jeep pulls 3rd gear on almost any grade I've been on now.

zstairlessone

a lot of people have had good results reprogramming the control module for the actual tire size after upsizing, it may help. Supposed to reprogram shift points. Anyone on here with an automatic that can verify this?

silverbullet88

Yeah I used one. Aev pro cal. It's eh