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Stick or auto?Originally Posted by jt1911
And which SC did you get?
This is my first post and after reading and reading, this is the place that seems to have the most informed folks. So, I just received my new SC for my 2014 rubicon. The press release that I read really emphasized correct gearing to get the tune right. I'm running 37" KM2's and this rig is a dailly driver. Thanks ahead of time for any help.
Stick or auto?
And which SC did you get?
It's an auto and it's the Magnuson 3.6L SC
To clarify my question, I'm looking for a relatively collective reply on gear ratio's that folks have found work well with 37's and the Magnuson SC on the 3.6L motor.
I have the Mag S/C on my 2013 JKU with automatic trans. I have 35s and 4.10 gears. If I had it to do over I would get 4.56 gears.
Everyone's got their own preferences about how their jeeps should drive. Keep in mind all JL power mods are on manual trans jeeps. Because it makes dyno testing far easier.
That being said, The auto is geared lower than the manual trans. So my position is to stay at 4.10 as the 37" KM2 (which i am VERY intimate with) is really a 35.5" tire. Im sure the OP had read the "truth about gears" thread, the rest of you reading this if you have gear questions, its a good reference based on my own misery.
Here's my answer. with 4.10 with the KM2 your RPM at 70 mph should be around 2288. (its the 35'' line). That is STILL more agressive than the stock rubi auto with 3.73 gearing- 2276. Chrysler offered the 3.73 gearing with the rubicon because they felt that it was the correct gearing with the new auto trans. They kept the 4.10 gearing as an option because people would have rioted in the streets if they didnt. Someone from AEV did a great article about it, I'll try to dig it up.
So lets subtract your SC. With or without the SC the 37 inch KM2 is a very light tire for its size and is not really 37". Your auto with 4.10 should have no problem turning them...happily. The SC just puts an exclamation point on it. It should spin those km2s with no problem. Hopefully your wheels are light also. Beadlocks may throw this off a bit if your trying to spin a 40lb wheel.
My point- In a case like this, my suggestion, is that you install the SC and live with it for 6 months. If your truck is a pig, (and it shouldnt be) then consider gearing. A LOT can go wrong with a gear change. you can have wrrrrrrrrrr noise, and other issues if the shop that does it, cuts a corner, or if a seal comes unseated. Snarf and I have both done gear changes and both of us have had small leaks to contend with. Just little nagging issues. Nothing terribly serious, but a pain in the butt none the less.
We all read these forums and think, the math says 37s = regear. Not so fast. The internet is flooded with old information and you need to do the math for yourself. I got caught in it, and went to 4.88s with 37s, and I wanted to kill myself with my truck spinning at 2800 rpm on the highway.
If you were at 3.21 I would say pull the trigger. I'd suggest no one for gears past Yukon, and feel that their customer service is fantastic, as they have had engineers on the phone with me trouble shooting my less than perfect install. No problems with my Yukon gears or axle kits, but the guy who put them in was a friend and not a shop, and you know how that goes.
hope this helps. Let us know what you decide.
What is it about the combo that you dont like? And, what sort of driving do you do? Your in NJ, so i have to guess you spend time on the highway. I ask because you have the auto and the mag, where as our mag is on a manual trans. Do you feel like your truck is slow?
So, first a thanks to jeeplab for the detailed reply. I was glad that I had that info before I picked my jeep up from the shop today. Having read that reply helped me keep an open mind as to what I might or could expect to see with my stock 4.10's turning the 37's. I will say that I wasn't completely disapointed with how it drove...more on that in a bit.
I wanted to take a minute to share my Rubicon project. I picked it up today after getting a big chunk of the parts installed. Here's the list so far:
Rock Krawler 2.5" X factor Lift
Fox 2.0 resevior shocks
Fox ATS steering stabilzer
Currie Anti-rock rear sway bar (for the Gobi rack/ARB tent)
Currie correctalink steering linkage
River Raider bumpers, fenders corner armor
Warn CTI-S winch
Method Race wheel beadlocks, custom powder coated
SPOD w/ G screen
Genesis Offroad dual battery kit
GOBI rack
Baja Designs Onyx Pro 30in and two 8in lights, S2's around the rack
Baja designs Squadron Pro lights for fromt bumper
Rockslide Eng power sliders
ARB CKMTA12 compressor w/ under seat mount
ARB drawer system w/ ARB 50 qt fridge
ARB sampson 3 tent and awning
Few iterior mods.
So, now that those parts are on, the supercharger, gears and possiblly driveshafts are what I have left. Driving home today from the shop allowed me time to evaluate how the jeep drove on the 37 in KM2's. It drove well and for the most part, I was pleased. There were more times that I found myself manually downshiftig on the route that I took back which consisted of a lot hills and some highway.
With Magnuson really stressing proper gearing, I'm left deciding if 4.56 would give back the "stock" feel in the shifting etc. With that info, what else do I need to consider?
You're correct. I spend most of my time on the highway (and mostly at or above 80 mph). My thought on going to 4.56 is because my auto trans is five speed. I would like all of my passing and acceleration at highway speed to be with a downshift to 4th gear. But to really "kick it in the guts" and push myself back in the seat I need to downshift to 3rd gear and let the motor spin up to 3,500 rpm and stand on it through 4,500 rpm and then either lift off the pedal to shift or use the auto-man to up-shift. I would hope that the lower gears would get the rpms up just enough to get have a bit more available power at the pedal in 4th gear.
I have 4.88 gears and running 35's nitro trail grapplers on my 2012 jk. Spent last weekend running Moab and drove it there from home, approximately 190 miles away. On the trail the gearing was perfect as we were rock crawling Prichett canyon (serious stuff). On the highway I wish I had another gear.. Going to jump up to 37-38's especially since the supercharger is being installed in two weeks. My suggestion is to go with 37's.
FF
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