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?Originally Posted by jt1911
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?
Now back to you Jt1911,
SC + AUTO + 37s + 4.10 = good drivablilty. Would it be better with 4.56? Maybe.
My own truck BB is
SC + Manual + 37s + 4.56
Do I love it? I'll tell you this. I hated the 4.88s. Took my rocket ship and turned it into a row boat. I struggled to get to 80 MPH, really struggled. Made me sick to drive her.
Is she now at 4.56 the highway cruiser she was with 4.10? when I'd cruise at 85mph at 2300 RPM in 6th gear? No. Ive lost her awesome effortless cruising speed. even dialing back to 4.56s. I cruise at 75 now.
Everyone's perception of what is "Good" is different. Jesse (snarf) and I have very similar builds, but we go in opposite directions on certain points like gearing. He likes more gear than I do. But he is also the kind of guy who dosent mind back roads. If im not on a highway cruising at 75 at least...I'm pissed.
You dont know what gear YOU will like until you live with gearing for a time. I say, live with your 4.10s for a while. If you hate it, consider 4.56. People will tell you, "if you want 4.56, you should just go to 4.88" Thats BS.
If you have 37inch KM2s, then look at the 35 inch line of the gear chart. And pick your gearing by where you want to cruise on the highway. You have a rubi, so your transfer case will make whatever gear you have 4.10, 4.56, 4.88 , low enough to wheel with anywhere in the united states.
Why force an up shift at 4500 rpm? This engine has 6500 of them available. Use them!
X2. wind it out to the end.
I will say, the whole "lift to shift" thing with these power mods is a fairly awful problem for an expensive power upgrade.
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