ok I have a 2009 JK 4 door and its weighted down pretty good (bumpers, winch, roof rack, ect) and im running 38's (yes to big) and I have 488 gears currently. I have a set of axels out of a 2002 F350 that are in the process of getting built to go under it now and im planning on going to a 5.38 gears. My issue is I currently pull a 12X6 trailer with a RZR4 900 and my RPMs are usually in the 3-3500 range to maitain 70mph. My question is what would help more out of these 3 options (or if you know something better then these options feel free to tell me)

1) dropping down to 35's
2) installing the new axles with 5.38 gears
3) installing a supercharger (looking at the Ripp)

 

Getting a proper tow vehicle.

Adding 500 lbs worth of axles is not going to help anything. A super charger would help, but I'd be really uncomfortable running one on that setup and then towing. That's a ton of constant load on a weak engine. That's also a lot to ask of stock axles.

 

I'd have to say gears based on your list. Going down to 35's is the same answer as "gears."

Dropping down in tire size numerically increases the effective gearing. Going up in tires size numerically decreases the effective gearing. So really, your choice is between some type of "gearing" change and the super charger.

I think forced induction is REALLY cool. Many manufacturers are doing some great things with it and maintaining GOOD tow ratings with a 4cyl and 6cyl engine with some type of forced induction. i.e. super/turbo charging

That being said, most tow vehicles start with 8 cylinders and then add forced induction i.e. turbo diesel. Cummins 6cyl diesel excepted. Seems most gasoline vehicles stick with 8 cylinders and 5L+ displacement.

I don't think forced induction on a JK is complimentary for towing unless it provides the torque LOW in the power band. Otherwise your twisting the engine on any slight up-hill grade.

Maybe best off going with 5.38 gears AND 35" tires on a 2nd set of rims. Throw your larger 38s in the trailer and swap at the trail head.

 

Automatic or manual transmission? 3500 rpm at 70 with 4.88's makes me wonder where you will with 5.38's especially with the possibility of going down to 35's. Going down in tire size will help with wind resistance at highway speed. Also lowering the suspension will help. Flat fenders? If so that is also creating more wind resistance.
You basically have a vehicle that is has many obstacles negating the towing ability.

 

yes I understand that it isnt a F350 tow rig but I was just trying to see what could help out some, but thanks for everyones input

 

You have a 3.8 auto with 4.88's now, and are running OD/Off to get those rpm's, correct? To me, that says you need both more power and proper gearing for the tire size.

I assume you have plugged the numbers into the chart in the faq's?

3.8 auto, 4.88's, 38's (using 37" for measured height)
OD On = 2141 rpm @ 70
OD Off = 3102 rpm @ 70 (od/on divided by .69)

Swap to 5.38
OD On = 2361 rpm @ 70
OD Off = 3421 rpm @ 70

Going to 5.38 doesn't even get you to 2400 rpm. And once it drops out of overdrive, the rpm's just keep climbing. You need more power if you want to stay in OD...



I didn't mention towing because I assume that a razr + trailer isn't anywhere close to the max tow limit?

 

Are you towing with the OD off?
If so you can turn the OD on once you get up to speed. I have been doing this for years towing my stuff around without any issues.
Unless there is an issue with using OD on the JK trans while towing I am not familiar with?

 

V8 with a 6speed is what you need or another vehicle, 3-3500 RPMs is crazy. Supercharger will give you more usable power to tow with but that's not going to make a difference in RPM's. Regearing isn't going to do much either, with the RPMs being so high your going to run the risk of burning up the transmission. If it's an automatic I hope you have installed a external Transmission cooler to keep the temps down. I'd drop to 35's until you find another vehicle to tow with, The less rotational mass should help a little but not much.