Is your 3.6 MT gutless on highway (w 37" tires + gear)

[Willing&Able]

I have a 2019 JLUR w 6 MT that is heavily modified - full teraflex LA kit, adam's driveshaft, rcv axles, etc. Also running 37" Toyo OC, a winch (heavy), and when out on the trails have a ROAM case and gear on my rhino rack pioneer. So I have some extra weight and more aerodynamic drag with gear on top. I have regeared to 4.88 to help offset.

On the highway (70-75mph) sixth gear is useless, I bleed speed even on flat highway stretches. Therefore I have to keep in fifth gear to maintain speed on flat. At even slight inclines (talking a few degrees over 100's of yards) even fifth will lose speed and I have to shift into fourth to maintain the speed limit. With the AC on it's even worse. In fourth I'm pulling 3000 rpm or so and w the AWE trail exhaust it is fairly loud (I knew this going in).

Having to be in fourth gear on the highway to maintain speed seems nuts for a nearly 300hp vehicle, even w the weight and drag. It feels like I'm running with half of that power.

Assume this is common and a 'Jeep thing'. Anyone else have the same issue? I understand there isn't much for power adders for the 3.6. I could regear to 5.13 but that is worse for highway driving - although may make fifth or sixth functional.

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[jlewissystem]

I dont seem to have that. I have 5.13s and typically use 5th gear (70-75) is about 3K and i have no issues accelerating, even with the AC on. If i go above 75, i can use 6th, but it's still usable. I am lifted with additional weight as well. I have never run 4.88s, but i wouldn't think there's that big of a difference.....maybe there is?

 

[Rico1111]

Mine is pretty much stock ....she is nimble and quick! As stated even with the ac on! I run usually 80's on the highway everyday to and fro work. Of course barring traffic!! I LOOOOOOVE this JL and if I ever need to lift or put bigger tires I will def regear.

 

[BullMoose1776]

If it makes you feel any better, I have the AT and it's really no different.

 

[mwilk012]

The problem is that your 300HP is at like 5k+ rpm. This engine lugs at low rpm, bad.

 

[Ridgway Jeeper]

At 3300 rpm you are only making 150 hp. Shouldn't be any surprise that it takes more than that to turn heavy 37" tires at highway speed. Did you really think it would be a good highway vehicle with 37's?

 

[AMKRubicon610]

I’m all stock manual trans besides my 35x12’s and method wheels.... it really didn’t feel any different than stock when I got the wheels and tires on. It cruises good on the highway, but once I hit around 80 mph I really start feeling the wind drag and there isn’t enough power/gear to compensate for it. I don’t intend on driving faster than that tho so it’s nbd lol

 

[Willing&Able]

At 3300 rpm you are only making 150 hp. Shouldn't be any surprise that it takes more than that to turn heavy 37" tires at highway speed. Did you really think it would be a good highway vehicle with 37's?

Of course not - hence the regear to help - but didn't think it would require driving in fourth gear when on the highway. Guess this is normal and no one has a solution other than to deal with it. Perhaps an engine swap!

 

[Ridgway Jeeper]

Of course not - hence the regear to help - but didn't think it would require driving in fourth gear when on the highway. Guess this is normal and no one has a solution other than to deal with it. Perhaps an engine swap!

Supercharger is way cheaper. Looks like they have them pretty well sorted now. Probably have to include another grand to upgrade to the Centerforce clutch too.

I think what you are experiencing is pretty normal. I think going to 5:13's for 37's would have made it better but that is still a lot of tire under a brick powered by a high revving DOHC motor. I wish we could buy these with a 5.7 Hemi and a six speed, I would have ponied up a few extra grand for that but a $30k swap isn't happening for me.

 

[Willing&Able]

I’m all stock manual trans besides my 35x12’s and method wheels.... it really didn’t feel any different than stock when I got the wheels and tires on. It cruises good on the highway, but once I hit around 80 mph I really start feeling the wind drag and there isn’t enough power/gear to compensate for it. I don’t intend on driving faster than that tho so it’s nbd lol

Supercharger is way cheaper. Looks like they have them pretty well sorted now. Probably have to include another grand to upgrade to the Centerforce clutch too.

I think what you are experiencing is pretty normal. I think going to 5:13's for 37's would have made it better but that is still a lot of tire under a brick powered by a high revving DOHC motor. I wish we could buy these with a 5.7 Hemi and a six speed, I would have ponied up a few extra grand for that but a $30k swap isn't happening for me.

I already have the Centerforce clutch - after three different versions. I hear mixed success - especially long term - on the JL SC. I read a few of the threads here and some took them out altogether. I can live it the way it is, just wanted to make sure something wasn't off... Sounds normal.

 

[Ridgway Jeeper]

I already have the Centerforce clutch - after three different versions. I hear mixed success - especially long term - on the JL SC. I read a few of the threads here and some took them out altogether. I can live it the way it is, just wanted to make sure something wasn't off... Sounds normal.

I would be perfectly comfortable with the Edelbrock set up. The guys having issues are almost universally trying to push a bigger than necessary blower using tunes from independent guys that do not have near the resources or reputation to protect that Edelbrock does. Living at 8000 feet I would for sure be looking at the SC if we wanted to go 37's. My real hurdle though it that with a couple inches lift and a couple more inches from the tires, I don't think it would fit in the garage anymore...

 

[intentsrig]

Yeah I have 5.13’s / Manual and 37’s. 6th is ok on flat ground if going above 70 but I’ll usually just stay in 5th at 70.

Soemtimes I can hold 5th for certain gradients but depends on how much gear I have and even wind direction lol.

Definitely a dog with bigger tires even with my Jeep likely being lighter than yours. Soft top or bikini in summer, no rear bumper, no racks or boxes in the wind, I wouldn’t waste the money to go to 5.13’s though.

 

[supermike]

yes, it is slow AF. I have rockkrawler 2.5 in lift 35 in ko2 method wheels, front and rear bumper, lod rock sliders, and bleed speed in 4th gear uphill. yes I'm still at 4.10.
ordered a 392, should solve my problem.

 

[Some Random Guy]

At stock I have the same problems you describe, which is why I scheduled to go deeper at 5.13 to match to 37’s (now 38.5’s). I really think higher highway RPM are just the cost of driving something less aerodynamic than a cow though. I’m hoping I can hold 5th for non-mountain gradients and just use 6th on flat ground post tire upgrade.

 

[AnnDee4444]

I could regear to 5.13 but that is worse for highway driving - although may make fifth or sixth functional.

Here's a rough estimate of the thrust the tire puts to the road vs. 4.88s (@ WOT).

4.10 & 37s in 5th gear = solid cyan
4.88 & 37s in 6th gear = dashed blue

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