Magnuson SC and proper gearing

[jt1911]

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.

[JeepLab]

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?

[jt1911]

It's an auto and it's the Magnuson 3.6L SC

[jt1911]

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.

[gbaumann]

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.

[JeepLab]

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.

1196

[JeepLab]

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.

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?

[jt1911]

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?

[gbaumann]

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?

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.

[ferrarifast]

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

[Pznivy]

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.



Is this guy serious with this list? Dude, you have been holding out on us! We need threads on all that stuff!!

Or at the very least a build thread with 10,000 pictures.

I love the stuff you picked.

[FLIPmeOVER]

Is this guy serious with this list? Dude, you have been holding out on us! We need threads on all that stuff!!

Or at the very least a build thread with 10,000 pictures.

I love the stuff you picked.

x2. Jt1911 is going to have to take the next week off work and post about all that gear. Is it a piece by piece build? or did you just go nuts with the credit card and morph a stock jeep into a monster overnight?

[JeepLab]

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

4.88 with 35s is a TON of gear. It was probably great in moab. But you will want to kill yourself in daily driving situations if traveling distance on highways.

Thats the whole thing with the north east. if you live here and want to really wheel, you have to be prepared to do 3 hours in the car. Knowing that you are overgeared and that 3 hours is going to be miserable with your truck spinning at 3k rpm to keep up with traffic, you will talk yourself out of wheeling all together. You need a blend of highway and offroad. Thats why the transfer case is a reason to get a rubi. You can maintain good off road gear, in 4LO but still have a livable truck on the highway.

[JeepLab]

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.

So let me know if I get this right.

SC + AUTO + 35s + 4.10 gearing = highway passing in 4rd gear?

SC + AUTO + 35s + 4.56 gearing = highway passing in 3rd gear?

Now, this all brings further questioning

1. Is your speedo calibrated perfectly?

2. What is the RPM you cruise at if doing 80mph?

baumann, Ive read your posts a bunch of times now trying to get clear about how to help the OP in this thread. Since you have the auto with the mag and we dont, your experience above ours in this case because of your AUTO transmission.


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.

Here is what I think about your situation, not Jt1911's.

I think are geared right. 4.10 for 35s with the SC is PERFECT gearing. If you had 4.56, you would feel overgeared. If you have never been overgeared, take it from me. It sucks. Do not feel like if you did it over again, you'd do it different. The grass is always greener on the other side of the fence. I promise, you are on the greener side of the fence. Being overgeared, turns your supercharged truck into a pig on the highway. I dont care how much horsepower you make.

If you had 4.56 with 35s on an Auto, you would be at 2700 RPM at 70 MPH! Your truck would struggle to get to 80, and would be gasping for air there at 3500 RPM. You would almost be forced to go to 37s.

Just my position. take it from a guy who geared twice.

[JeepLab]

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.

[UselessPickles]

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.

Why force an up shift at 4500 rpm? This engine has 6500 of them available. Use them!

[gbaumann]

[QUOTE=JeepLab;3125]So let me know if I get this right.

SC + AUTO + 35s + 4.10 gearing = highway passing in 4rd gear?

SC + AUTO + 35s + 4.56 gearing = highway passing in 3rd gear?

Now, this all brings further questioning

1. Is your speedo calibrated perfectly?

2. What is the RPM you cruise at if doing 80mph?

baumann, Ive read your posts a bunch of times now trying to get clear about how to help the OP in this thread. Since you have the auto with the mag and we dont, your experience above ours in this case because of your AUTO transmission.[QUOTE=JeepLab;3125]

OK.

SC + AUTO + 35s + 4.10 gearing = highway passing (65 mph to 80 mph) in 3rd gear. I use auto-man to go to 3rd and that lets me get the throttle open enough to get boost up. 4th gear is problematic when passing. Even in auto-man if I pass in 4th gear the trans will downshift when accelerator is depressed beyond a certain point. It won't stay in 4th. The downshift from 4th sometimes jumps two gears to 2nd! That's not safe for me or the motor. So to stay safe I go to 3rd. Yes, I can pass in 4th but it takes much more distance and not at all uphill. Again, there is probably more power available in 4th gear but I can't access it because opening the throttle enough to close the SC bypass and get into full boost will cause an unwanted downshift. I'm thinking that 4.56s will get rpms up in 4th a bit and reduce the downshifting. A better solution would be to get access to the transmission side of the PCM and reprogram automatic trans shift-points and keep my 4.10s. But I hear that's not going to happen for a long time if ever based on how difficult it is to crack Chrysler's PCM transmission programming.e

I'll record my rpms at 80 today and report back.

[jt1911]

Hey guys, sorry for the delay with pics, work schedule has been crazy. Thanks again for continued information. One of the things I wanted to wait and see what effect there was, was throwing the GOBI rack on top. One thing that I've been thinking about was how much weight I've added to my jeep. I installed the rack just yesterday and I love it, but man that thing is a pig. I was able to drive the jeep for two days without the rack and a short road trip yesterday with it.

I thin the added weight from everything is something that has pushed my decision to go with 4.56's. Now, I do not spend a lot of time on the hwy and when I did, I wasn't hammering 80mph regularly. Most of my driving is backroads. That being said, with the terrain around here, there's a lot of up and downs and I was annoyed at how I had to push up to 4500 rpm to get a gear change. But, The SC wil be getting installed in two weeks and I'm goon wait and see how she does with 4.10's and then I'll make my mind up at that point.

So.. for pics, can anyone chime in with simple directions? never posted pics before..

[jt1911]

12171218121912201221

[jt1911]

Figured it out..I think

[Yoinkers]

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.

[JeepLab]

12171218121912201221

The truck is very well done. I like the rack a lot.

Are all your parts steel? flares, rails, armor, rack, bumpers, tire carrier?

If so, you may want to consider the 4.88s. expecially if you dont spend much time on the highway.

[jt1911]

Everything is steel which is why I mentioned the weight thing with the rack. I don't have the exact figure on tool weight added, but it's obviously several hundred pounds. The only thing I weighed were the Method rims which with headlocks came in at 31lbs each. I don't remember what the KM2's are per tire, but I had read your (jeep lab) previous post on wheel mass did try to keep the combo as light as I could.

With more time behind the wheel today, the 4.56's were for sure going in but I was thinking about 4.88's. The question is do I get the SC installed and wheel it with the tune that's installed a the time, or go ahead re-gear and set the tune up with 4.88's?

I'll throw another wrench in the plans; do i stay with stock exhaust and air intake or upgrade? Not that I need it, but I like the looks, but how would a snorkel effect the tune on this SC?

[JeepLab]

Everything is steel which is why I mentioned the weight thing with the rack. I don't have the exact figure on tool weight added, but it's obviously several hundred pounds. The only thing I weighed were the Method rims which with headlocks came in at 31lbs each. I don't remember what the KM2's are per tire, but I had read your (jeep lab) previous post on wheel mass did try to keep the combo as light as I could.

With more time behind the wheel today, the 4.56's were for sure going in but I was thinking about 4.88's. The question is do I get the SC installed and wheel it with the tune that's installed a the time, or go ahead re-gear and set the tune up with 4.88's?

I'll throw another wrench in the plans; do i stay with stock exhaust and air intake or upgrade? Not that I need it, but I like the looks, but how would a snorkel effect the tune on this SC?

1. Those have to be the lightest beadlocks on earth, and the KM2 is 70 lbs. Ive never heard of a 30lb beadlock. Im not saying its not, Im saying if it is, Its super light.

2. I say gear after SC. Dont worry about the tune. The tune is for air fuel mixture in the engine. Your gear change will not effect it.

3. Stock exhaust vs. aftermarket is no difference in performance as far as my testing has shown. If someone else has better info on it give us a chart.

4. Mag planned for a snorkel, so dont hesitate to use one if you want to. BUT keep in mind, even if your snorkel is installed correctly, if you hit a bump in the future and somehow loosen it, you will allow water into your engine through the connection to the snorkel.

[gbaumann]

So let me know if I get this right.

SC + AUTO + 35s + 4.10 gearing = highway passing in 4rd gear?

SC + AUTO + 35s + 4.56 gearing = highway passing in 3rd gear?

Now, this all brings further questioning

1. Is your speedo calibrated perfectly?

2. What is the RPM you cruise at if doing 80mph?

baumann, Ive read your posts a bunch of times now trying to get clear about how to help the OP in this thread. Since you have the auto with the mag and we dont, your experience above ours in this case because of your AUTO transmission.



Here is what I think about your situation, not Jt1911's.

I think are geared right. 4.10 for 35s with the SC is PERFECT gearing. If you had 4.56, you would feel overgeared. If you have never been overgeared, take it from me. It sucks. Do not feel like if you did it over again, you'd do it different. The grass is always greener on the other side of the fence. I promise, you are on the greener side of the fence. Being overgeared, turns your supercharged truck into a pig on the highway. I dont care how much horsepower you make.

If you had 4.56 with 35s on an Auto, you would be at 2700 RPM at 70 MPH! Your truck would struggle to get to 80, and would be gasping for air there at 3500 RPM. You would almost be forced to go to 37s.

Just my position. take it from a guy who geared twice.

With 35s and 4.10 gearing with automatic trans I'm running around 2,700 (2,750?) at 80 mph. That's in 5th gear, of course.

[gbaumann]

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.

Well. . . I don't mind winding her up now and again and I'm fully prepared to drop a hemi in if the 3.6L S/C blows up. But I don't want to sprint down that path. Remember that we're running open deck aluminum blocks with iron sleeves. The bottom end of the pentastar is by all accounts rock solid and built to take forced induction. The heads and the upper deck aren't. At least not in the Jeep version. They will accommodate forced induction but we need to be careful. Static compression ratio is, I think, 10.5:1. With 6 to 8 lbs of boost you can quickly get north of a 14.0:1 effective compression ratio. That's O-ring head gasket territory and closed deck block architecture land. Oh, and that kind of cylinder pressure would LOVE 100 octane fuel. When these motors are in route from Pentastar to Masarati where they are fitted with twin turbos they first stop off at Ferrari where the cast blocks are machined and they receive different heads. I've read that the cylinder walls are fortified and the sleeves are thickened which reduces displacement to 3.2L. I think some of this technology is rumored to be headed for a few Chrysler products in the future. I even heard that there could be turbocharged Pentastar RAM pickup truck. So what does all of this have to do with gearing?

I was originally attracted to the MAG SC because of the flat torque curve and how quickly it developed power in the RPM band. I want that power at lower RPMs to be transmitted to the road. As I push down on the accelerator I want to be pushed back in my seat. Not downshift two gears. At 65 mph I want to drop one gear and disappear! I would love to get the throttle open more in higher gears so the motor has to develop the power the SC is capable of producing. With my 4.10 gearing, 35s and an auto trans, I'm mostly using 3rd gear to find power. The trans will hold that gear and let me open the throttle so the SC can develop power. And it's quite awesome! I would like a little of that awesomness in 4th gear too. I was wondering if 4.56s would get me there. But from what I've read in this thread I don't think new gears are the answer. I think I have a good ratio and need better transmission control.

[jt1911]

Jeeplab, as far as the Methods…they were weighed on my scale in the house. I will say, that I put 50lbs on the scale to verify the weight and the beadlocks came in at 31lbs roughly. Not to say that I didn't screw something up by how I placed the wheel on the scale, but it read 31-32lbs. Thanks for the all of the info. I'll keep you posted on how the SC instal goes. Anyone else, please feel free to chime in, the more info the better.

[JeepLab]

Jeeplab, as far as the Methods…they were weighed on my scale in the house. I will say, that I put 50lbs on the scale to verify the weight and the beadlocks came in at 31lbs roughly. Not to say that I didn't screw something up by how I placed the wheel on the scale, but it read 31-32lbs. Thanks for the all of the info. I'll keep you posted on how the SC instal goes. Anyone else, please feel free to chime in, the more info the better.

Method Race Wheels confirmed it. I talked to steve there today. 32 lbs for those beadlocks.

That is an incredibly light beadlock.

Really good wheel pick. Bravo!

[jt1911]

Good deal, glad I wasn't off on my weights. Since having installed them, I've checked the torque settings every day and for the most part they are holding. Now if I can just get all of my baja design lights wired up. Anyone have a weather pack connector crimping tool?