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Discussion Starter #1
Hey there fellow jeepers, so I'm at the age old debate about what to do with this 3.8.

I have an 07 JKU, completely overhauled suspension, 3.5 lift and 35s. Manual trans, 4:10 gears on D44 front and rear. Nothing too crazy. And let me add that the ONLY issue Ive ever had with my 3.8 is that I cant go 60mph up a hill in 6th gear, and I live in the hills!!

So I've been looking into getting some more power under the hood, and I've come up with these 4 options, all of which have their own pros and cons.

RIPP SC the 3.8 for about 6K.
Hemi conversion for a whopping 23K
3.6 conversion for almost as much(cant find an exact price)
Or a 4BT swap for a chunk of change I dont even wanna get into.

I know my BEST option would be a hemi conversion, but cmon, how many of us have 23k just to throw into something like this.

Does anyone have any long term. Experience with the RIPP black ops pushing 11psi? (Seems like a slow sure death of the 3.8)

At the end of it all, I'm curious to see how long this 3.8 will last the way I drive it. So i don't need to swap it. Just curious to see everyone's input

And please don't tell me to go buy a new jeep.. I've put too much effort into my jeep and I've been through a LOT of trails and parks with this thing and have plans to conquer the whole country with it. Swapping jeeps is simply not an option.
 

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Just a re-gear would prolly solve your hill problems.
If you have an itch to spend money while you're in there changing gears, add some lockers, RCVs/axle shafts, and big brakes. You'll prolly spend slightly less than getting a SC. Just sayin'.
Worry about that 3.8 when it gets tired.
 

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I have an 09 that's at 141k miles and it's been supercharged with the Ripp kit since 65k miles. I'm on 38s with 4.88 gears and I think it does great. I have the auto trans, so there's that annoyance, but otherwise I'm good with it. It's about as quick as a 3.6l JL stock, which is ok with me until the motor goes. My Jeep does burn almost a quart of oil every 4-5k miles. Idk if that has anything to do with it being supercharged.

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Discussion Starter #4
Just a re-gear would prolly solve your hill problems.
If you have an itch to spend money while you're in there changing gears, add some lockers, RCVs/axle shafts, and big brakes. You'll prolly spend slightly less than getting a SC. Just sayin'.
Worry about that 3.8 when it gets tired.
What gear would you recommend? I already have lockers and shafts though. Lol
 

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I have an 09 that's at 141k miles and it's been supercharged with the Ripp kit since 65k miles. I'm on 38s with 4.88 gears and I think it does great. I have the auto trans, so there's that annoyance, but otherwise I'm good with it. It's about as quick as a 3.6l JL stock, which is ok with me until the motor goes. My Jeep does burn almost a quart of oil every 4-5k miles. Idk if that has anything to do with it being supercharged.

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No RIPP based engine issues yet? Mines already burning a quart through oil changes so I'm used to that!
 

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Not that I can tell! Somewhere around 120k, my oil I drained for an oil change smelled like there was a good bit of fuel in it. I thought I was having blow-by issues, but I just filled it up and did another oil change early a couple thousand miles later to check and all was fine. Hasn't happened again. Change my oil every 4-5k miles and the supercharger oil every 10k.

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I have to agree with @funfred with a regear. It will be the cheapest options to regain some of your performance loss.
 

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If you want to be able to drive up hills at 60MPH in top gear, don't get a RIPP. That's the wrong kind of supercharger for that goal. RIPP is a centrifugal supercharger which gives huge boost at high RPM, but very little at the more useful street RPM. It's great at the track, but you still have to down-shift on the highway. It gives a little boost down low but not that much.

You want a twin screw or TVS supercharger for your goal. Edelbrock, Sprintex, etc.

Also regarding your thought of a 3.6L swap, I don't think I'd recommend that. It's not a plug and play swap, you have to do a significant amount of re-wiring work and maybe even have to scrap all the electronics from the vehicle and do a custom setup. As far as I know, there is no 3.8 -> 3.6 swap kit. If you're going through all that work, there's really no reason to not put some V8 platform in.
 

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RPM said they are close to a 3.6 swap:

We are finishing up the 3.6 standalone. We have added in a ton of features. The full standalone 3.6-wa580 (nag1) will be able to control a Jeep JK style cluster on its own, making a gauge setup very easy in a older vehicle. It will also have AC request, AC PSI and compressor controls built in. This will make adding air conditioning quick and easy. We also added in FUEL LEVEL based on a JK fuel sender that will show the correct fuel level on the cluster and 4wd switch input that will tell the system when its in 4wd, 2wd, N and 4low.

Once we finalize the 3.6 standalone with will work on the 07-11 JK 3.8 to 3.6 conversion. This will be a fully integrated system and will utilize all the early JK systems to work with the 3.6. This will be a lot simpler than a standalone because the JK already has the ABS-Wheel speed sensors to drive the transmission and the TIPM has everything else we need to control the AC and gauges. It will be like your early JK came with a 3.6 from the factory and should be 100% emissions compliant in California.

After that we may look at the JL 18+ 3.6 with the 8 speed. The 8 speed runs on a newer computer system and is fully electronic, including the shifter. There is no shifter cable which has been shown to cause issues in the JL-JT at times. We will have to determine what modules the newer system needs to make it operate correctly.

For now the 3.6 5 speed auto is a great choice to upgrade the 3.8. They are cheap and there are a ton of them to purchase with a lot of guys going to a V8.
 

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What gear would you recommend? I already have lockers and shafts though. Lol
I can't make that recommendation - I have no experience with the 3.8, but...

If you had the space to run it flat out in whatever gear allows you to pull redline, you'd have some figures to play with that could get you into the ballpark. Take note of the gear and rpm when your Jeep stops pulling. You'll likely need a secluded (no traffic) and relatively long, flat stretch of asphalt.

Let's say you can pull 4th to redline or a little over. 5th is a couple hundred/500 rpm down and 6th is off by a thousand+ rpm. Do the math and figure out what gearing would allow you to pull 6th gear the same as you pull 4th or 5th, that is, pulling 6th to/near redline. Look at the two available gearings that are above and below the number you come up with and pick one that better suits your thinking for overall use. Your number might be really close to a standard ratio making your choice easier.

Use the link below to help yourself. It's really handy for determining what ratios one might want based on tire size, known dyno curves or just comparing different tire sizes and their effects on ratios, etc. The drop down menu in Step 1 is nearly all inclusive when it comes to transmissions and I think it's Step 4 that does transfer cases. You'll need to know your differential gear ratio. The RPM and SPEED can be adjusted on the tables at the bottom and they'll spit out the mathematical answers.
You may want to input your actual, real world tire diameter as Dunlop's 35 ain't the same as Bridgestone's 35 and neither measures exactly 35 inches.
While you may play with the idea of "how fast can I go if I put 37s on with 3.42 gears?", the reality is that this spreadsheet is academic and in no way accounts for hills, aerodynamic drag or vehicle hp/torque...there's no way any of our jeeps are doing 200mph. :D

As a bonus, giving your Jeep an easier gear to pull might have the added benefit of increasing its gas mileage, as counter-intuitive as that may sound.

 

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I've had the RIPP with Alt pulley on for 30k miles with zero major issues with the motor. I don't daily drive it and that 30k has been across 6 years, but I do thoroughly enjoy giving it hell on the rocks, so I give the little 3.8 a good workout a few times a year. I have an auto, 5.38s, with 41.5s and it doesn't have any issues spinning the tires to heat them up. As mentioned above though, the boost is not down low, it comes on higher in the RPM, I would prefer it to be instant for more usable torque in my application but I'm not redoing the powerplant for a TVS until I swap in couple more cylinders.
 

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What gear would you recommend? I already have lockers and shafts though. Lol
For 3.8l, 6MT,.and 35s, I can recommend 4.88s with full confidence.
If you think you might go 37s, --> 5.13s are your huckleberry.

Fun Fact: the difference between 4.10 and 4.88 is ~the same as your NSG-370's O/D ratio.
Therefore, if you want to "test drive" 4.88s for free on the highway, don't use 6th gear.
Within a few RPM, that's what you'd get in 6th (also, every other gear gets 20% lower).

EDIT: adding "the chart" from way back when -
363992
 

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Not sure if the "new" JKO would allow me to attach a spreadsheet, but here's a screenshot of a calculator I whipped up:

363993


Assuming your 35s are effectively 34.5", this should give you a good idea of what gears are useful for what MPH with 4.88s.

EDIT: yeah, nah - can't upload the Excel. If you're going to use an online calculator, the trans. ratios in my screen shot are gospel for an '07-'11 3.8l JK's NSG-370 transmission.
 

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My 3.8 is turning out to be akin to the honda fourtrax 300...it will not die.

i can tell you i swapped 37” cooper stt pro/17” spyderlocks for 37” MTRK/17” methods...lost 112lbs of unsprung weight...yes you read that correct. Regeared to 5.13 from the factory 3.73 and it is like a new vehicle...around town. You can now pull out in front of someone and not worry about getting ran over.

buuuut, when you need some oomph to pass at highway speeds...it’s still nothing. Literally just fawking nothing. IMO the entire drivetrain just need ripped out, put something real in there...idt it’ll cost 23k if you are able to do it yourself(I understand a big IF, i know i will need some assistance with this one)
 

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Discussion Starter #15
My 3.8 is turning out to be akin to the honda fourtrax 300...it will not die.

i can tell you i swapped 37” cooper stt pro/17” spyderlocks for 37” MTRK/17” methods...lost 112lbs of unsprung weight...yes you read that correct. Regeared to 5.13 from the factory 3.73 and it is like a new vehicle...around town. You can now pull out in front of someone and not worry about getting ran over.

buuuut, when you need some oomph to pass at highway speeds...it’s still nothing. Literally just fawking nothing. IMO the entire drivetrain just need ripped out, put something real in there...idt it’ll cost 23k if you are able to do it yourself(I understand a big IF, i know i will need some assistance with this one)

Im fully capable to do it myself but i honestly dk about what i would do other than add HP to the engine and a regear. Aside from the 23K statement, Im leaning more towards a supercharger at the moment, ive narrowed it down to either a ripp or sprintex, currently doing a F-load of research on both. 23K is just way too much for me to even think about right now, im gonna build the 3.8 and run it until it dies and honestly probably drop in a fresh one if i like the HP gain from a SC.

Theroretically though, i agree, my 3.8, trans, and axles should all be shot right now from what ive put this thing through.
 

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I agree with Christensent. Does anyone have a graph of the roots style? Usually the roots style gives you more low end torque, which is what you need to climb hills in 6th.
 

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dt it’ll cost 23k if you are able to do it yourself
Im fully capable to do it myself
If you can do it yourself, you get a hemi in there for far less than 23K

 

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Hey there fellow jeepers, so I'm at the age old debate about what to do with this 3.8.

I have an 07 JKU, completely overhauled suspension, 3.5 lift and 35s. Manual trans, 4:10 gears on D44 front and rear. Nothing too crazy. And let me add that the ONLY issue Ive ever had with my 3.8 is that I cant go 60mph up a hill in 6th gear, and I live in the hills!!

So I've been looking into getting some more power under the hood, and I've come up with these 4 options, all of which have their own pros and cons.

RIPP SC the 3.8 for about 6K.
Hemi conversion for a whopping 23K
3.6 conversion for almost as much(cant find an exact price)
Or a 4BT swap for a chunk of change I dont even wanna get into.

I know my BEST option would be a hemi conversion, but cmon, how many of us have 23k just to throw into something like this.

Does anyone have any long term. Experience with the RIPP black ops pushing 11psi? (Seems like a slow sure death of the 3.8)

At the end of it all, I'm curious to see how long this 3.8 will last the way I drive it. So i don't need to swap it. Just curious to see everyone's input

And please don't tell me to go buy a new jeep.. I've put too much effort into my jeep and I've been through a LOT of trails and parks with this thing and have plans to conquer the whole country with it. Swapping jeeps is simply not an option.
Hey there fellow jeepers, so I'm at the age old debate about what to do with this 3.8.

I have an 07 JKU, completely overhauled suspension, 3.5 lift and 35s. Manual trans, 4:10 gears on D44 front and rear. Nothing too crazy. And let me add that the ONLY issue Ive ever had with my 3.8 is that I cant go 60mph up a hill in 6th gear, and I live in the hills!!

So I've been looking into getting some more power under the hood, and I've come up with these 4 options, all of which have their own pros and cons.

RIPP SC the 3.8 for about 6K.
Hemi conversion for a whopping 23K
3.6 conversion for almost as much(cant find an exact price)
Or a 4BT swap for a chunk of change I dont even wanna get into.

I know my BEST option would be a hemi conversion, but cmon, how many of us have 23k just to throw into something like this.

Does anyone have any long term. Experience with the RIPP black ops pushing 11psi? (Seems like a slow sure death of the 3.8)

At the end of it all, I'm curious to see how long this 3.8 will last the way I drive it. So i don't need to swap it. Just curious to see everyone's input

And please don't tell me to go buy a new jeep.. I've put too much effort into my jeep and I've been through a LOT of trails and parks with this thing and have plans to conquer the whole country with it. Swapping jeeps is simply not an option.
Supercharger is nice just make sure you get custom tunes instead of the ones they have programmed better performance I know you probably dont want to hear this if my 3.8 craps out it will get a LS SWAP reliable parts are dime a dozen
 
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