Gleep,
I always lean back on asking yourself what you want out of the vehicle. There are many routes you could choose. Depending on your location and emission requirements (or lack thereof), you could even swap in a VW TDI, TWS (although I have no first-hand experience) seems like they build the Rover V8 into something awesome, but so much of this depends on you. What is your budget? What will you do with the vehicle once you are done? What amount of the work do you want to do yourself? Answer some of those before diving one direction or another. Just so you have some reference, I am in the midst of LS swapping mine. I will be approximately $10K into it. That is with a 5.3 and a 6L90. That is with extremely minimal outsourcing of anything but essentials. Let me know if you need more information to better answer these questions for yourself.

 

Did you need a 4x4 or 2wd 6l90 and did it require a tear down to replace the output shaft? Plenty of clearance for the prop shaft along the transmission/bell housing?

 

Rick,
That's one of the few times I had to call in help. I had a 4x4 version. I tore down the trans to rebuild it and sent the output shaft out to Moser to be turned/resplined to fit the Mark's adapter spud shaft. I then discovered that the 4x4 output shaft is too narrow in diameter, and I had to have a 2wd output shaft sent to them. All is well that ends well, but the 6l80 would have been easier.

As far as clearances go, most guys with the 6L80 have had to chop off the tab on the trans connector to get it to fit with the prop shaft yoke. The 6L90's length made that a non-issue. The front prop shaft has plenty of clearance all around. The length really became an issue with the parking brake drum and clearance at the front. I am adapting the drum to a disc setup. We'll see how that turns out. The engine has enough space, but only just at the front. In summation, I would recommend the 6L80 as it helps with several of the issues I ran into. I was blinded by a smoking deal on the 6L90 core (I didn't want to spend the $2,800 that most used 6L80s were going for) so I bought it up right away.

I also used a Gen 3 LS converted to "act" like a Gen 4. I saved some money that way. Currently, I have the tach/crank signal working without any black box or interface. I am praying I figured out something for traction control, but I have an ABS problem that I need to fix before I can test that.

Gen 3 LS truck power steering pump fitting screwed right into the current Rover lines.

Let me know if you have any other questions. My goal with this build was to make it as close to the cost of the ACE kit, but with the GM 6 speed. I am approaching the end, but not quite there yet.
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So if I'm reading correctly if you had the 2wd model 6l90 there would have been no mods needed to fit the adapter? I'm looking at the axis adapter (not positive on the name) located in the USA.

I'm planning on using a VW TDI matched to the 6 speeds. More hears = easier time keeping TDI motor between 2000-3000 rpms where she is happiest making good torque. The TDI is a very short engine so keeps the transfer case in the stock location shouldn't be an issue.

I greatly appreciate the feedback, by chance are you willing to share how you got the tach running? I'm assuming the Speedo works off of abs or the transfer case so no issues there with the swap.

 

Rick,
You will have to check the adapter. I couldn't find the one you mentioned. I know Advance Adapters sells Mark's 4wd kit. The 6L90 is listed as an option, but it needs to be a 32 spline output shaft. The funny part is, GM never made it with a 32 spline output shaft. The 2wd is 29 spline if I remember correctly, and it is large enough in diameter to be turned and resplined. Short answer, no. No version of the 6L90 output shaft will work with the 32 spline adapter. I believe Moser charged me in the realm of $150 plus shipping to have the shaft machined. So it can be made to work, but the 6L80 is the only one with a 32 spline output from the factory. I thought about using the 6L80 output, but the output is tied into the rear ring gear. I can't remember if it is possible, but even if it is, you lose some of the strength of the 90 by converting to the 80 output planetary set. At that point, it didn't seem worth the hassle.
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I'm jealous. TDI was one option I would have loved, but not worth the hassle with the emissions nannies. Just easier to keep gas to gas swap. That will be awesome though!

I'm happy to share any part of my build. I kept the LR ECU to use as my "black box". The LR crank sensor is a two wire AC signal. The tooth count on the LR reluctor is 58x(58 teeth with a space). The Gen 4 GM LS uses a 58x reluctor as well. It is a digital signal. I tapped the one wire from the GM signal and attached it to the pink wire on the LR crank wiring. The rest was unused. I believe this is how the ACE kit was doing it. They used the factory sensor and a 58x reluctor on the crank balancer. I do could not find any info for the VW. If it utilizes the same reluctor count, you could potentially do the same. There are other ways to accomplish it, but they are obviously more complicated.

The speedometer runs on the ABS sensors. You are correct and that is a non issue. The coolant temp sensor threads straight into a plug on the LS cylinder head. I'm sure you could rig something up with the VW as well. I believe that is the extent of the factory dash. Of course you need to tap the check engine light wire as well.

 

We do have the advantage of an inspection free state.

​​​​​​Thank you for the information.

The only part that is worrisome for me is the power reduction in the factory tune of these transmissions, at least in the 6l80.

It reduced engine power between shifts which prevents the transmission from harming itself. While I'll rarely ever get the TDI over 3000 rpms she does make 300 ft lbs of torque at 2000 rpms.

I'm not able to reproduce this split second power reduction between shifts as the only communication between the engine and transmission via a stand alone TCU is TPS and RPM.

This is about the only hold back I've come across before buying parts...other than the TDI engine

 

Hmm, I have even thought about that. Using all GM allows me to use HPTuners to make any of those adjustments I need. I am seeing Zero Gravity Performance may offer something that allows for some control. Holley's offering looks like it also needs their Terminator X ECU to operate properly.
I really trust these guys as far as transmission stuff is concerned https://www.sonnax.com/parts/3505-zip-kit. I think if you installed this zip kit, the 1-2-3-4 piston, and a torque converter with a billet lid, you should be set. I would check with Zero Gravity and see what adjustments are possible with their kit. They say it can't be utilized with the Cummins 4bt and some others. Might be worth reaching out.

 

I have spoken to zero gravity, he said the power reduction is a non issue. A local tuner who makes his bread and butter off of the LS platform disagrees.

 

I wonder if you could utilize the GM computer, supply as much as is necessary to run the transmission, and then tune it that way. It would sort of be the same scenario as the LR ECU. Just a passthrough device. If you can feed it rpm, TPS, MAF, and MAP, that may be all that is required to run the trans, and you can tune it for the specifics of the TDI. I know that's some additional wiring and fab work, but it may ensure you are able to make the necessary adjustments .

 

I have looked into this as well. I tend to agree more with your local tuner. The 6L80 / 6L90 and these modern transmissions are clutch-to-clutch designs, and they require more precise control to shift properly. I don't think the modern designs shift as well without the power reduction. Many of the 3rd party controllers (like the PCS that Zero Gravity sells) do not appear to be able to interface with engine ECUs to cause the power reduction.

On the older transmissions, like the 4L80, and the 4HP series that don't have a clutch-to-clutch design, I don't think the power reduction matters.