Higher horses, higher revs & even higher torque, a streetable LJ engine swap

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As far as transmissions go, there's 2 main automatic transmission families that mate with the LS. The 4L family is based off of the older 1980s TH400 design: 4L60/4L70/4L75 is the same physical size and the 4L80 is slightly larger. And the 6L family which is a new design since 2006: 6L80 and the slightly larger 6L90. There's more models and history, but that's the important bit.

There's a lot of 4L60/70/80(e) Jeep builds out there and that transmission has been around for a long time now. It's a proven transmission for swaps based on the already proven TH400 that works and doesn't have many complaints (as long as the weaker versions aren't overloaded). Going with a 4L75e would be a huge improvement over my Jeep 4 speed 42RLE.

4l75e gearing:
4l75-gears.jpg


The 6L80e seems to be better not only because it has 2 more gears, but because it's an entire generation newer than the 4L and everything internal is redesigned and improved. From all of my research and discussions with everyone who's played with both the 4l75e and 6l80e says that the 6L is just better even though they admit the 4L is good too. An interesting tidbit that I came across is that Levi Shirley is using a 6L80e transmission behind his 700hp LSX with a 3:1 transfercase and runs races in low range over 100mph.

6l80e gearing:
6l80-gears.jpg


Comparing both with a gear chart:
gear-ratio-comparison.png

(If this image is too small, click here)

Here's my comparison and thought process deciding between the 6L80e and the 4L75e. Take it all with a grain of sand because this is all just internet research and not my first hand experience.
  1. Both can come configured with the LS3 crate engine and thus will be compatible and easy to tune (...hopefully...).
  2. Both are rated to the same strength of 650lb-ft of torque (this is about 40% more than the production versions).
  3. Both have a similar overdrive top gear for the highway.
  4. Both can be adapted to an Atlas transfercase
  5. The 6L80e has a lower 1st gear and, with my 37" tires and 5.38 gears, Advance Adapters recommends a 3:1 transfer case, for the 4L70 Advance Adapters recommends a 4:1 transfer case. Although it seems that you could upshift early into 2nd with the 6L80e and 4:1 TC?
  6. Both have been fit into long wheelbase Jeeps before.
  7. Both can use tap shift and be forced to stay in a gear.
  8. The 4L can be adapted to use a manual valve body (not beneficial for most of where I'll be going)
  9. Both can be setup with a mode for towing, different shift table for 4low, and the 6L80e also has a "sport mode" (I'm not entirely sure these modes will be beneficial for me).
  10. The 4l70e is proven to work well with a 4low shift table, the people using the 6l80e seem to be using the high range shift table and are reporting good results.
  11. The 6L80e requires only a few wires be connected because the TCM is wired internally. I think this can help with reliability too since there's less exposed wires to get damaged (although a good wire loom could also work fine).
  12. Supposedly the 6L80e can self learn weird shift behavior, and can need to be reset (if for example it's learning period is while bombing sand dunes but then you drive on the road).
  13. The 6l80e will probably get better MPG due to more gears and a modern higher efficiency shift design (not a huge pro for me as long as I can get at least 200 mile range on the highway or spend a day on the trail without running out of gas, but gas savings is a nice bonus).
  14. The 6L80e has better gearing for driving between obstacles while still in low range.
  15. The 4L70e weighs ~50lbs less than the 6L80e (the 42RLE weighs about the same as the 6L80e).
  16. The 6l80e does hang ~1.25" lower than the 4l75e with the truck pan. If it ends up being too deep there are multiple shallower pans from car applications which can save up to 1" at the expense of losing a quart of fluid. Supposedly the Shirley's are running the shallow G8 pan. If they aren't having problems with it, I won't be. (the stock Jeep 42rle transmission from the centerline of the transmission to the bottom of the pan is roughly 8". The 6l80e is ~9.2")
  17. The final concern is that if the 6L80e is too wide, a front driver's side drop driveshaft will have a lot of issues getting around it. This is an issue with high uptravel builds that also have a high pinion axle and something I dealt with my 42RLE. Thankfully I found several comparison pictures:

    4L70 vs 6L90 (the 90 case is slightly different from the 80):

    A6%20Trial%20000ee.jpg


    rsz288 LS1Tech (https://ls1tech.com/forums/conversions-hybrids/898899-6l80-6l90-into-68-camaro-does-go.html)

    4L60 vs 6L80:

    4L60%20VS%206L80-TOP-%20VIEW-2.jpg


    4L60%20VS%206L80-SIDE%20VIEW-2.jpg


    Goat1 Pirate4x4 (https://www.pirate4x4.com/threads/which-6-0l-trans-combo-to-go-with.1747945/page-2#post-26192233)

    6L80e truck pan vs G8 pan:

    6L80%20TRUCK%20VS%20G8%20PAN.jpg


    Goat1 Pirate4x4 (https://www.pirate4x4.com/threads/k...a-4-build-thread.1104481/page-5#post-15045419)

After a lot of deliberation, comparison, and conversations I decided to go with the automatic 6 speed 6L80e transmission paired with the LS3 directly from Chevy as part of their Connect and Cruise combo kits. For my uses it seems to be the better transmission and by buying it married to the engine everything will be compatible. I don't know enough about why but the LS3/480 6L80e kit only comes with the higher 3000-3400k stall speed converter. The LS3 430 comes with the 2400-2800k stall torque converter.
 
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I have started ordering parts!

From the sounds of it, the crate engine and transmission will ship within a couple of days from placing the order and then arrive here within a week or two via Fedex Freight. So to maximize the warranty period I'll be ordering it once I have all of the other major supporting parts on their way.

My initial plan was to figure out what parts I need over the summer and get stuff ordered in time to pull my engine out once the snow starts flying again around November. So this build thread may have a slow start. If parts come in early I'll start right away. In the meantime I've removed the supercharger off my stock 4.0L and I have a few adventures planned! I also have my wife's well built khaki TJR on 35s to play around with once the red LJ is under the knife.

Here's my shopping list and notes so far (this list is subject to change).

  • Radiator: Superior Radiator - I've heard this one lasts longer than others do. (http://rover.ebay.com/rover/1/711-5...0001&campid=5337789113&icep_item=164219718305)
  • Water pump + tensioner: I will buy OEM (must fit above radiator and be truck or f-body offset)
  • Harmonic Balancer with correct offset: Does anyone know the difference between OEM and the performance balancers such as ATI?
  • Accessory brackets: I'll be going with GoatBuilt's driver's side brackets for the alternator and PSC CBR pump (truck or f-body offset)
  • Power steering pump: I'll be reusing my CBR pump off the TJ 4.0 but will need a 6" pulley offset for the LS.
  • AC bracket: Holley low-profile or Dave's Customs high mount.
  • Alternator:
  • Transmission shifter: I'm undecided between a Winters + tap or using an OEM tap shifter. It'll probably come down to what fits best.
  • Engine mounts: There's no mounting kits that will work for me so I'll use universal style brackets and make my own.
  • Trans/TC mounts:
  • Engine oil pan:
  • Engine oil: 5w30 synthetic. Break in oil first?
  • Transmission fluid:
  • Radiator coolant:
  • Transfer case: Atlas 2 speed (I still need to configure this)
  • Transfer case fluid:
  • Dash gauges:
  • Ignition switch: Is it possible to retain the stock keyed ignition on the steering column?
 
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This site contains affiliate links for which Jeep Wrangler TJ Forum may be compensated.
It looks like the longest lead time item will be the Atlas at 6-8 weeks until it ships. So I think I should get that ordered ASAP.

@mrblaine do you have any advice on configuring the Atlas?
 
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toximus said:
The 4L can be adapted to use a manual valve body (not beneficial for most of where I'll be going)
Click to expand...
Well, getting into reverse quickly is a huge life saver. A manual valve body and differnt shift pattern with a matched gate can save your rig/life if the occasion was to show it’s self.

just something to consider.

I would encourage you to stay away from the 4L60E. It’s a bit of a stretch to prove a point, but Reid doesnt build an aftermarket case for the 4L60E...but they do offer a 4L80E and TH400 version if that says anything.

Maximum seems to be a go to for the Ultra4 guys and trophy truck guys. Wouldn't hurt to give him and call and discuss your requirements. he has a lot of Real world knowledge And wrench time with the 4WD rock crawling/rock racing transmissions. This is what drew me to his shop for my build.

2wd, and you can get away with the smaller tranmissions. Add 4wd, big tires, beadlocks, big axles, and a transfer case and it creates a division. My .02

Edit: Never mind me, just read your entire post and read that already made your decision. Good choice.
 
Fouledplugs said:
Well, getting into reverse quickly is a huge life saver. A manual valve body and differnt shift pattern with a matched gate can save your rig/life if the occasion was to show it’s self.
Click to expand...

I agree there and I wouldn't mind a reverse valve body. But having to manually shift driving across the country isn't my cup of tea and a lot of places off road I prefer to let the automatic take care of things while I focus on driving. Having both would be ideal and that's where TUTD will help bridge the gap.

I'm looking at doing PRND21 (6 position shifter). PRND will function as expected. 2 will be manual (TUTD). 1 will be 2nd gear start for when you don't want the trans to shift right away.

Fouledplugs said:
2wd, and you can get away with the smaller tranmissions. Add 4wd, big tires, beadlocks, big axles, and a transfer case and it creates a division. My .02
Click to expand...

For sure. If for some reason I can't fit the 6L80e in, for my build and 500hp engine I'd only consider the 4L75e or 4L80e.

Fouledplugs said:
That would be my concern.
Click to expand...

I expect that I'll still need a smaller diameter front driveshaft. It won't be an issue of strength, but I will still have to unlock the front hubs when I go over 45mph or so.
 
toximus said:
I'm looking at doing PRND21 (6 position shifter). PRND will function as expected. 2 will be manual (TUTD). 1 will be 2nd gear start for when you don't want the trans to shift right away.
Click to expand...
Most of the guys I wheel with that have v8 swapped are using the winters shifter from WOD. Then set it up for the bottom most position to be manual (3) and next up to be auto (4). Some of them cut off the lockout between 4 and 3 for a quick slam up to reverse. This is a pic of one done with the Rad Designs tap shift kit.

ebd22871f4afde5fcf2fb03f556bb8b7.jpg
 
jesseshoots said:
Most of the guys I wheel with that have v8 swapped are using the winters shifter from WOD. Then set it up for the bottom most position to be manual (3) and next up to be auto (4). Some of them cut off the lockout between 4 and 3 for a quick slam up to reverse. This is a pic of one done with the Rad Designs tap shift kit.

View attachment 170035
Click to expand...

I'll have to ask them if they can do the same thing but with an extra position.
 
toximus said:
I'll have to ask them if they can do the same thing but with an extra position.
Click to expand...
They're really nice and knowledgeable folks. I know they're running into supply issues right now, but give them a call and see what the lead time is.

The tap shift kit blocks out the lower two positions so I'm sure you could figure something out.
 
I just called. The RAD tap shifter switches can't have the shifter behind them or they break so he can't do a 6 position.
 
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