MrClortho

Hello, new to the forum but not to Jeeps and I have a simple observation if anyone is interested.

I picked up a '17 JKU Sport, automatic, 3.73 gears replacing a '12 JKU Sport, 6 speed, 3.73 gears. Both have 33" BFG AT tires and the 3.6L. My '12 had a K&N cold air and cat-back exhaust, but the '17 is all stock.

I am a manual transmission guy but the 6 speed in my '12 was quite possibly the worst feeling transmission I have ever had, nothing like the TJ's butter smooth stick. I disliked it so much that I opted for the automatic this time around. Now, taking out the discussion about how I would rather choose my gear than letting the transmission do so, the automatic runs better on the highway for sure.

With the 6 speed, 80 mph was not easy to hold without downshifting up every hill. Out in west Texas, on a windy day, on an 80 mph highway, I could not hold the speed limit unless I was in 4th with the engine rapped out if at all. I always thought it just didn't run that great for having all that horsepower advertised.

The automatic has significantly more power on the highway, or at least acts like it, and holds speed much easier. I suppose the rpm, torque multiplying, etc... difference is significant but there is no doubt that this '17 feels like it has quite a bit more power at highway speeds. You would think the '12, with its modifications, would have run better. Maybe the mods were actually hurting the torque?

At any rate, I thought that was an interesting 'real world' observation.

Monte417

First off those mods you mentioned are not going to give you any additional real horsepower. Second I have a 12 manual and don't ever see myself downshifting frequently on the highway in 6th gear especially going 80mph. Did I read right the you downshift to 4th going 80mph to get up hills? Gearing shouldn't be a problem as you are only running 33s so when in the 80s you are running some pretty high Rpms. I can see maybe downshifting to 5th at the least to get up a pretty long and steep grade but that's it. I know you won't be able to hold 80 but 65 plus should not be a problem

rob_engineer

I have a 2012 jku Sport manual trans with 3.73 gears. I never have a problem maintaining highway speeds. Mine is basically all stock except for a steel rear bumper. I live in NJ and drove all along the east coast and inland as far as Pittsburgh. In fact, I just got back from the mountains of Virginia where I towed a 7x14 enclosed trailer with a '69 dune buggy inside. I had to keep it in 5th and maintained a 65mph speed while towing. I too wonder if you hurt the highway power with the mods you made. Did you have armor? Did you have the stock air dam, or was it removed?

MrClortho

Hmm, I did have a stubby with rock rails on the '12 so added wind resistance and weight there. It also had the Pentastar head issue and was in the shop more than once for that.

I have a 2" lift, winch plate, K&N replacement filter, and rock rails on the way for the '17. After I install all of it, it will be interesting to note how its highway performance is effected.

rob_engineer

I have a coworker with a 2012 jkur. He installed 1" leveling pucks in front. He took his to dealer because he was getting very low MPG. The dealer told him it was because of the 1" lift. I call B.S. on that. However, anything that makes the Brick be more like a brick is going to hurt performance against wind at highway speeds. The air dam is one important feature that helps to make it less like a brick.

MrClortho

I hear that, which is why I went with a winch plate on the stock bumper instead of a stubby this time...to keep that air dam and have a little bit of wind deflection on the tires.

bushpilot

interesting observations - i have a '12 w/ the 6 speed manual and 3.21 gears
i also find that theres not enough torque at 80 mph (or even slower) to maintain speeds on even moderate hills.