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

omnitonic

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This thread has been an eye-opener. I would have thought 4.88s would be sufficient to get the use of all six gears, even on 37s. Obviously not. It seems everybody faces the same enemy here, and it's the torque curve of this engine. Well, I can't afford to do anything about that problem, so here's to winding the hell out of 4th gear. Cheers.
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This thread has been an eye-opener. I would have thought 4.88s would be sufficient to get the use of all six gears, even on 37s. Obviously not. It seems everybody faces the same enemy here, and it's the torque curve of this engine. Well, I can't afford to do anything about that problem, so here's to winding the hell out of 4th gear. Cheers.
i kinda scratch my head on the idea that some folks want this thing to haul’ass with big’ass tires….Them two things are inversely related.
 

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i kinda scratch my head on the idea that some folks want this thing to haul’ass with big’ass tires….Them two things are inversely related.
Especially the dogshit MT and 3.6. At least with the 2.0 you get low end torque and more gears assuming the AT trans. MTs belong in sports cars.
 

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Especially the dogshit MT and 3.6. At least with the 2.0 you get low end torque and more gears assuming the AT trans. MTs belong in sports cars.
Or not go fast trucks… or in vehicles that are fun to control, not meant for best QTs to the nearby piggly’wiggly.
 

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I too have the 3.6/MT combo but my JLR is a little lighter, probably scales 5,900 with us, gear and the dogs. I've also got 35x11.5's with the factory 4.10 gears. It cruises just fine in 6th on the hiway. Climbing the grapevine out of LA I had to drop to 5th and even 4th in a couple of spots if traffic wasn't moving well... So why are our results so different?

I know octane is a touchy subject, but I've been running premium since new. In another thread I recently learned that if your are running regular the ECU could be pulling as much as 8.5 degrees of advance out. Six of this is in the long term table so... You might try filling up with premium and resetting the ECU (not sure how, but I assume by disconnecting the battery overnight). It will take the ECU a while to relearn your diving style, but it seems like a worthwhile experiment...
 
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I think I've found a big culprit - the ROAM case on top. I did some highway driving w some gear but without the box up top and it was somewhat better - able to keep cruise steady in fifth the whole time. Sixth still struggled. I knew there would be drag, but it seems to be a bigger deal than expected...

I was wondering if there could be something off w the motor itself - i.e. lowered compression in a cylinder, etc.

And for the responses of 'did you expect it to be good on the highway' - yes, I did expect to be able to use all my gears. I'm not looking to overtake people with one downshift. I am expecting some use out of sixth and for fifth to hold steady on cruise.

And MT only for sports cars....what?
 
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Willing&Able

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Picture of case for reference...

IMG_5593.JPG
 

Wbino

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My stock v6e is quick at take off and has 8th gear on highway aplenty.
This is mall crawler territory......
 
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Willing&Able

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My stock v6e is quick at take off and has 8th gear on highway aplenty.
This is mall crawler territory......
8th gear = auto trans, so not relevant to discussion.

Mall crawler territory? I haven't seen a lot of full teraflex builds with RCV axles, Adam's driveshafts, etc. hanging around at the mall. That picture was my sons and I just leaving for a 300 mile off road trail from northern WI to the tip of the UP Michigan past Copper Harbor. Didn't pass a mall!
 

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i kinda scratch my head on the idea that some folks want this thing to haul’ass with big’ass tires….Them two things are inversely related.
My observation was that a Jeep on 37s with 4.88 gears is just as bad as my stock 32s with 3.45 gears. I'm just trying to drive the speed limit in top gear, and that is not achievable with the stock configuration.
 
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Willing&Able

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My observation was that a Jeep on 37s with 4.88 gears is just as bad as my stock 32s with 3.45 gears. I'm just trying to drive the speed limit in top gear, and that is not achievable with the stock configuration.
This man gets it.
 
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Willing&Able

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What octane gas are you running? Also, is your air cleaner in good shape?
I run the highest available octane. In my area that is 93. Out on the trails it is typically 91.

Good call on the air cleaner. I've likely done 1000 miles off road over the last year or so which includes water/mud up north and desert out west.

I'll likely replace - what's the best replacement filter? I'm not looking for a CAI for 'whooshing' noises - I need to keep it protected from the elements.
 

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My observation was that a Jeep on 37s with 4.88 gears is just as bad as my stock 32s with 3.45 gears. I'm just trying to drive the speed limit in top gear, and that is not achievable with the stock configuration.
I know there's more to it than just engine RPM, bigger nobbies have more wind and rolling resistance, but GrimmJeeper says at 70 MPH in 6th gear:
1,826 RPM - 32's with 3.45 gears
1,984 RPM - 35's with 4.10 gears (me)
2,234 RPM - 37's with 4.88's (OP)

Looking at the torque curves @AnnDee4444 posted here:
https://www.jlwranglerforums.com/forum/threads/3-6-torque-curves.62669/page-3#post-1545438
We see you are well and truly out of the power band and I'm not much better off. But @Willing&Able is maybe 10% below the torque peak. So why does mine cruise just fine and his fall on it's face? This doesn't add up which is why I was looking for something like retarded timing or a plugged air cleaner...
 
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Willing&Able

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I know there's more to it than just engine RPM, bigger nobbies have more wind and rolling resistance, but GrimmJeeper says at 70 MPH in 6th gear:
1,826 RPM - 32's with 3.45 gears
1,984 RPM - 35's with 4.10 gears (me)
2,234 RPM - 37's with 4.88's (OP)

Looking at the torque curves @AnnDee4444 posted here:
https://www.jlwranglerforums.com/forum/threads/3-6-torque-curves.62669/page-3#post-1545438
We see you are well and truly out of the power band and I'm not much better off. But @Willing&Able is maybe 10% below the torque peak. So why does mine cruise just fine and his fall on it's face? This doesn't add up which is why I was looking for something like retarded timing or a plugged air cleaner...
I think aerodynamic drag is a big variable the above doesn't capture too. It was noticeable on the butt dyno when driving without all my gear up top. It would be an interesting experiment for me to time 50-70mph in 5th gear w nothing up top vs fully loaded. Suspect it is 15-30 sec difference in time.
 
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