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

[toximus]

I ordered an Atlas 2 speed transfer case and the 6L80e adapter (#50-9600) from Advance Adapters.

I decided on a 3:1 ratio to go with the deep gearing of the 6L80e. As seen by the engine this will be roughly similar gearing as a 4:1 transfer case behind the stock TJ or the 4L70 transmission. If I later decide that it's not enough gear the Atlas can be regeared to a different ratio.

For the rear yoke I'm switching to a 1350 joint. This will be stronger than the current 1310 and will better put up with shock loading when getting rowdy with the V8. In the front I'm likely still going to be running a 1.25" driveshaft to clear the transmission and engine and the smallest 1350 driveshaft Tom Woods makes is 2" diameter so I'll be sticking with the 1310 joint up front. Once I get everything in, if I find that I can run a 2" shaft I'll switch the yoke out to 1350.

For the tailhousing there were multiple pros and cons of each choice. Since my engine and transmission computers do not understand what low range is, the computers can not correct the dash speedo when in low range. The GM VSS tailhousing could be used for the dash gauge so it'd always report the correct speed but I can't remember a time that I've looked at what speed I'm going while in low range so I think it'd add unnecessary cost and wiring (although not hard to do if your OCD requires a correct dash speedo). There's also the "standard tailhousing" which allows for the use of a Jeep speedo which could be useful if I were retaining the stock Jeep dash. Since I didn't see a benefit in either of those I decided on the short tailhousing which is cheaper and 2" shorter than the standard tailhousing. With the 4L-series transmissions I'm pretty sure having the GM VSS tailhousing is required.

I also specced the case with a sight tube, 4wd switch, and low range switch (although I'm not positive I'll be using these switches yet. As an experienced Jeeper I can't think of a reason to keep the 4wd light on the dash since it'd be pretty obvious if the transfer case didn't go into 4wd or if I forgot to take it out of 4wd on the street?). If I decide that I want a different shift table for low range I can use the low range switch to trigger the 6L80e's tow/haul mode and put my low range table in there.

 

[Apparition]

I ordered an Atlas 2 speed transfer case and the 6L80e adapter (#50-9600) from Advance Adapters.

I decided on a 3:1 ratio to go with the deep gearing of the 6L80e. As seen by the engine this will be roughly similar gearing as a 4:1 transfer case behind the stock TJ or the 4L70 transmission. If I later decide that it's not enough gear the Atlas can be regeared to a different ratio.

For the rear yoke I'm switching to a 1350 joint. This will be stronger than the current 1310 and will better put up with shock loading when getting rowdy with the V8. In the front I'm likely still going to be running a 1.25" driveshaft to clear the transmission and engine and the smallest 1350 driveshaft Tom Woods makes is 2" diameter so I'll be sticking with the 1310 joint up front. Once I get everything in, if I find that I can run a 2" shaft I'll switch the yoke out to 1350.

For the tailhousing there were multiple pros and cons of each choice. Since my engine and transmission computers do not understand what low range is, the computers can not correct the dash speedo when in low range. The GM VSS tailhousing could be used for the dash gauge so it'd always report the correct speed but I can't remember a time that I've looked at what speed I'm going while in low range so I think it'd add unnecessary cost and wiring (although not hard to do if your OCD requires a correct dash speedo). There's also the "standard tailhousing" which allows for the use of a Jeep speedo which could be useful if I were retaining the stock Jeep dash. Since I didn't see a benefit in either of those I decided on the short tailhousing which is cheaper and 2" shorter than the standard tailhousing. With the 4L-series transmissions I'm pretty sure having the GM VSS tailhousing is required.

I also specced the case with a sight tube, 4wd switch, and low range switch (although I'm not positive I'll be using these switches yet. As an experienced Jeeper I can't think of a reason to keep the 4wd light on the dash since it'd be pretty obvious if the transfer case didn't go into 4wd or if I forgot to take it out of 4wd on the street?). If I decide that I want a different shift table for low range I can use the low range switch to trigger the 6L80e's tow/haul mode and put my low range table in there.

I believe Ian Johnson recommends using a gps driven speedo on engine swaps. He has one in the LJ he built for trail to Sema. I know he has a video on it but can’t recall where I saw it. May have been motortrend on demand.

 

[toximus]

I believe Ian Johnson recommends using a gps driven speedo on engine swaps. He has one in the LJ he built for trail to Sema. I know he has a video on it but can’t recall where I saw it. May have been motortrend on demand.

I'm curious what his reasoning is. Was that in his GoatBuilt LJ videos?

 

[Apparition]

I'm curious what his reasoning is. Was that in his GoatBuilt LJ videos?

I can’t recall which videos he discussed it. It’s on that rig though.

 

[jesseshoots]

You could use a driveshaft speed sensor similar to what circle track/drag cars use if you were really worried about it. Basically a cog and hall-effect sensor.

 

[Apparition]

I'm curious what his reasoning is. Was that in his GoatBuilt LJ videos?

Check here he has a link to it (on the Facebook page) so it must be in the video

https://www.facebook.com/video.php?v=219950555755461

https://www.autometer.com/universal-gps-speedometer-interface-module.html

 

[toximus]

You could use a driveshaft speed sensor similar to what circle track/drag cars use if you were really worried about it. Basically a cog and hall-effect sensor.

I don't need the extra driveshaft length and could have gone with the GM VSS tailhousing for an extra $100. I just couldn't think of an actual reason to go for it.

 

[jesseshoots]

I don't need the extra driveshaft length and could have gone with the GM VSS tailhousing for an extra $100. I just couldn't think of an actual reason to go for it.

The only reason I would go with it would be due to my OCD. Outside of that, the only reason would be to keep the odometer accurate.

I wonder if it would be possible to put together some sort of circuit to tack on a correction factor to the signal going to ecu/pcm that dictates mileage? I remember reading about one somewhere on here. You could tie that into the low gear switch you got.

 

[toximus]

The only reason I would go with it would be due to my OCD. Outside of that, the only reason would be to keep the odometer accurate.

I wonder if it would be possible to put together some sort of circuit to tack on a correction factor to the signal going to ecu/pcm that dictates mileage? I remember reading about one somewhere on here. You could tie that into the low gear switch you got.

From what I understand the 6L80e uses the internal VSS for tracking all of that. So even if I used a tailhousing VSS for the dash speedo, the odometer would still be incorrect. There's also different harnesses so my 2wd connect and cruise harness may be the limitation here, I don't know. Obviously they're running this transmission in trucks and SUVs so there must be some way if you use a production 6L80e.

Don't get me wrong, it'd be nice to have it all working perfectly, but it's not worth losing sleep over.

I have 0 plans to ever resell this Jeep or engine so an overstated odometer won't be a problem as far as that's concerned (and I'm sure any buyer interested in this type of Jeep would understand). I've always mentally kept track of maintenance based on hours and trips for this Jeep anyway so I don't think it'll mess up my maintenance schedule too much.

 

[toximus]

Check here he has a link to it (on the Facebook page) so it must be in the video

https://www.facebook.com/video.php?v=219950555755461

https://www.autometer.com/universal-gps-speedometer-interface-module.html

It sounds like this is more for road use and not <10mph. My speedo will work just fine in high range because the 6L80e has an internal VSS.

I suppose if I'm driving 60mph down the highway in low range it could be nice, but I don't think that'll happen often.

 

[Apparition]

It sounds like this is more for road use and not <10mph. My speedo will work just fine in high range because the 6L80e has an internal VSS.

I suppose if I'm driving 60mph down the highway in low range it could be nice, but I don't think that'll happen often.

I didn’t recall the specifics. Can’t say I’ve ever cared for my speedometer reading much below 10mph.

 

[toximus]

After being in low range all weekend I can say for certain that I didn't look at the speedo once. As long as I remove any speed governor off the ECU I don't see missing it. I also don't see missing the 4x4 light once the shift levers have positive positions... it's actually more distracting being lit than not.

 

[toximus]

Just in case you guys are interested in my updated shopping list. I'll probably be doing a huge order on Summit during their next sale.

1. Radiator fan: Spal 16" (waiting on engine harness to confirm wiring schematic since I'd like to go with PWM)
2. Water pump + tensioner: I will buy OEM (must fit above radiator and be truck or f-body offset) also need a thermostat?
3. Harmonic Balancer with correct offset: F-Body offset: ACDelco (OEM) 12553118, Truck offset: ACDelco (OEM) 19300488. Replace TTY bolt.
4. AC bracket: Holley low-profile or Dave's Customs high mount. I'll get the engine in before deciding which will fit.
5. Transmission shifter: I'd like a 6 position. I'm undecided between a Winters + tap or using an OEM tap shifter. It'll probably come down to what fits best.
6. Engine oil pan: Kevko or Tilden/Pacific.
7. Oil filter relocation kit: Wait on pan.
8. Transmission fluid: Dexron VI
9. Radiator coolant: Decide between G05 (HOAT) or Dexcool (OAT).
10. Dash gauges: Maybe Autometer for essentials + Torque app for other stuff? I don't love how Autometer gauges look.
11. Exhaust headers: CTS-V + heat shields (waiting to order until I have a visual on how the engine fits)
12. Engine oil: 5w30 synthetic Amsoil (leftover from the Jeep 4.0). Driven Racing 5w30 Break in oil first (optional, but not a bad idea).
13. A ton of bolts for attaching enginey parts to the engine.
14. Air filter: I'm waiting to see what space I have left to fit it in.

Ordered:

1. 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)
2. 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)
3. Power steering pump: I'll be reusing my CBR pump off the TJ 4.0 and bought a 6" pulley offset for the LS.
4. Alternator: Mechman high output alternator (probably overkill but 180a at idle will be awesome for heavy winching).
5. Transfer case: Atlas 2 speed 3:1
6. Transfer case fluid: Comes with Atlas.
7. Ignition switch: Retain the stock keyed ignition on the steering column.
8. Spark plug boot pliers
9. Engine mounts: There's no mounting kits that will work for me so I'll use universal style brackets and make my own.
10. Trans/TC mounts: AutoFab bushings

I also need an engine hoist and to replace my recalled Harbor Freight jack stands.

I'll probably use pallets and wood for an engine stand since it won't spend much time outside of the Jeep.

 

[gaabbee]

Question about the 3:1 vs 4:1. Why not just go 4:1 off the bat? If the 4.02 1st is too low then the 2.36 2nd gear isn't far off from the 3:1 using 1st gear. (12.06 vs 9.44). Not sure what kind of off roading you do which maybe I missed. Personally I would rather have the option of the 4:1 1st gear ratio and if not needed just use 2nd. The 3rd gear and 4th gear ratios are even closer.

 

[toximus]

Question about the 3:1 vs 4:1. Why not just go 4:1 off the bat? If the 4.02 1st is too low then the 2.36 2nd gear isn't far off from the 3:1 using 1st gear. (12.06 vs 9.44). Not sure what kind of off roading you do which maybe I missed. Personally I would rather have the option of the 4:1 1st gear ratio and if not needed just use 2nd. The 3rd gear and 4th gear ratios are even closer.

The wheeling I do is a little of everything. I had a difficult time deciding which to go with and I could be wrong. I went with 3:1 because the final drive ratio closely resembles 4:1 with the 4L70 trans which I know works well (or rather 3.8:1 in the Atlas).

 

[gaabbee]

The wheeling I do is a little of everything. I had a difficult time deciding which to go with and I could be wrong. I went with 3:1 because the final drive ratio closely resembles 4:1 with the 4L70 trans which I know works well (or rather 3.8:1 in the Atlas).

View attachment 171644

Ok I guess I just look at it a little differently. I see the 6 speed ratios as giving you a lower first gear and a higher overdrive vs the 4 speed. I feel by going with the 3:1 you've now matched the 4 speed ratios in gears 1-4 and now have 2 extra overdrives.

The reason I liked the 6l80 over the 4l75 was because of the gearing in 1st and 6th. Thinking of it more as a 4 speed with gears tacked on the front and back. Does that make sense? The 2 extra overdrives don't help me off road but that 82.39 crawl may.

 

[toximus]

Gotcha. I see what you're saying. My only concerns are that 1st would be too deep and I'd constantly be using 2nd even in the rocks, and then 3rd would be oddly placed for loose hill climbs.

My khaki TJ has the Rubicon 4:1 and Rubicrawler 2.72:1 (giving a combined 10.88:1). It's been a while since I've put both in low so I'm going to give them a try today and see how it feels. 1st will be final drive ratio of 166:1 (I've never found any reason to go that deep), 2nd will be 91:1 which will be closer to the 82:1 we're discussing for the 6L80e and 3.8:1.

Does anyone have experience with a 82:1 final drive ratio? Perfect or too deep?

 

[gaabbee]

Gotcha. I see what you're saying. My only concerns are that 1st would be too deep and I'd constantly be using 2nd even in the rocks, and then 3rd would be oddly placed for loose hill climbs.

My khaki TJ has the Rubicon 4:1 and Rubicrawler 2.72:1 (giving a combined 10.88:1). It's been a while since I've put both in low so I'm going to give them a try today and see how it feels. 1st will be final drive ratio of 166:1 (I've never found any reason to go that deep), 2nd will be 91:1 which will be closer to the 82:1 we're discussing for the 6L80e and 3.8:1.

Does anyone have experience with a 82:1 final drive ratio? Perfect or too deep?

That's not far off to the manual Rubicon's crawl around 73:1. The new rubi's are like 84:1. Your second gear would be similar to an auto rubicon, I think its 55:1

 

[toximus]

I did some testing in the khaki TJ (42RLE, Rubi 4:1, Rubicrawler, 5.38 gears, 35s):

As I already mentioned, a final drive ratio of 166:1 is stupidly deep and just wants to fight the brakes. It requires shifting into neutral to stop. Other than showing off how slow your Jeep can idle I don't see a point in it.

91:1 FDR may be okay for crawling and doesn't require any throttle input to move and the brake input required to slow down is quite a bit. Driving between obstacles I think I'd be shifting gears often.

Thinking back to Johnson Valley last year with the khaki TJ (and I'll admit I only went on the easy rock trails) 4:1 seemed to be a sweet spot, I tried the Rubicrawler and it was too deep, I used high range between rock gardens, across the lake bed and sandy hills (looking back the 2.72:1 ratio of the Rubicrawler could have been nice for the sandy hills).

Snow wheeling I think 4:1 on the khaki TJ is pretty good since it allows for consistent wheel speed whether the tires are grabbing or slipping and prevents "launching" and "bogging" every time the tires find traction.

Someplace like Moab where rocks don't shift and you don't have to find traction it may be a different story.

—-

When I think through this last weekend of loose dirty/rocky hill climbs in my red LJ (42RLE, NP231 2.72:1, 5.38 gears, 37s) I was in low range all weekend. For descending hills I enjoyed putting it into 1st (41:1 FDR) but for climbing I always wanted it in 2nd (22:1 FDR). Aside from the 4.0 engine not reving fast enough into 2nd, I thought it was a pretty good combo. Between trails 3rd (14:1 FDR) was often used. With the 6L80e and 3:1, that's 2nd, 3rd and 5th, or 6L80e and 3.8:1 that's 2nd, 4th and 6th. If I had a manual valve body I could see that working, but I'm not sure how the TUTD computer controlled 6L80e will like that.

A few weekends ago with my red LJ, we went slower with lots of firm ruts, huge holes, large roots and downed trees, and gravel ups and downs. And I felt that I could have used a deeper gear ratio then the 2:72:1 (41:1 FDR) which the 6L80e and 3:1 Atlas will provide in 1st (65:1 FDR).

 

[jesseshoots]

I find myself wanting more out of my first gear (47.5:1) in terms of slow speed crawling but wanting something between it and second (28.9:1) for the majority of the trails. I have AX-15, NP231, 4:56 gears, 35" tires

I think the 6L80 and 3:1 Atlas will be the sweet spot.