XJ6 Series 3 LS3 upgrade

Hi all,

I’ve been reading lots of posts on the forum for a while and learning a lot (great information here), however this is my first post.

I recently bought a 1984 XJ6 Series 3 Vanden Plas to upgrade with an LS3. This is my 2nd Jag, the 1st was an XJ40 that I owned for a few years and sold in 1999 (traded in on a Porsche 928, that I still have). I loved the ride, comfort and style of the XJ40, but always wondered about better performance.

This current car needs some TLC. The paint is good in places and poor in others and there is a little bit of rust around the rear window (and possibly in other places I haven’t discovered yet) and there are a couple of small spots of panel damage. The engine runs, but is not 100%.

No rust in the floor or inside the boot. The interior is so-so and could do with a refresh of the seat leather.

The purchase price was reasonable compared to some of the others I saw.

xj6 1

I am excited and anxious at the same time and look forward to sharing the experience, as well learning from you all.



Welcome to the forum Elias.
Looking forward to seeing your progress.
Keep us posted.


Thank you Aristides,

This is the donor car, an Australian-made “Commodore VF Series II SSV Redline 2014”. It was classified as unrepairable by the insurer.

I am having the Chev 6.2L LS3 engine and 6L80e auto trans + computers / wiring removed at the moment.

com 1


the 4l60e clears the floor pan without much persuasion, i suspect with the bigger 6l80e, you’ll need to enlarge the trans tunnel quite a bit.
has the 6l80 been used in a lump before?

I did see another post where one was fitted into an XJ-S.

The advice I have from someone that has done it before is that it will fit without modification to the trans tunnel. Hope to confirm that here shortly.

Donor car has now been stripped out. This is the LS3 and gearbox that will be going into the Jag.

Unfortunately the workshop is pretty busy and I will have to wait a little while for them to start tackling the next stage.

1 Like

Welcome from a fellow LS swapper!

I can’t speak to the 6L80E, but I was able to install a 4L80E behind an iron block 6.0 with no major modification to the tunnel sheetmetal in my '84 XJ6. I did have to trim some of the original brackets for the trans crossmember, and hammer in the tunnel to clear the electrical plug.

Some info for you…

I would also recommend going to ls1tech.com as that is the authority for all things LS swap.

i recently discovered the 6L80e is smaller and lighter than the 4l80e.
i believe the 6l80 will hold 650hp in stock form. Also you can get paddle shifters to work with it, should you choose to go that route

Thanks Norbert,
How far along are you with your swap? I would be keen to follow a thread if you have one going.

I managed to get a 3:31 LSD from an XJS V12 that I will be installing. The engine donor car had a 3:27 with the 6L80E, so a 3:31 should work well.

I’ll have a look at ls1tech as well.

Jay-Coole that is good to know.

My mechanic suggested installing the floor shifter setup that came with the 6L80E to see if I can use sports mode and tap shifting, which I won’t be able to do with the XJ shifter.

The 3.31 LSD out of the V12 is a great ratio

I am uncertain what GB ratios are in the 6L

If you had plenty of OD ratio, I would go as low as you can on the diff, I have a 3.54 LSD

One of my previous SUV had 4.55 D44 (almost identical to Jags)

Once or twice I would bore up some LS owning Commodore, I thought they had 3.09

In any case, the diff ratio and low end torque made up for the lesser engine power

You are no doubt aware of all this :smiley:

some older models, and 2.8 XJ had 4.09

I sold a 4.09 to a V12 racer

It is finished (are they ever really finished?) and I’ve been driving it for a bit over a year.

1 Like

The rations on the 6L80e are:
1st: 4.02, 2nd: 2.36, 3rd: 1.53, 4th: 1.15, 5th: 0.85, 6th: 0.67, so 2 o/drive gears.

I thought I had found a 3:54, but it turned out to be non-LSD.
I’ve driven SS commodores with the 6L80e and 3.27 diff and it seemed ok so fingers crossed.

Turbos LS? Wow… Thanks for the link, I’ll be reading through your journey in detail.

I keep telling myself a Stage 1 / Stage 2 setup of CAI (maybe a mild cam / new valve springs), exhaust and a tune, which should get me up close to 500hp, will be plenty of power. And then I drift off into what if I had a turbo… or an LSA supercharger… :slight_smile:

But I’ve decided to wait till I drive it and I suspect Stage 1 / Stage 2 will be more than enough. I’m not a young lad anymore…

i did an LS1 in my '71 XJ6 with custom cam, 92mm intake, headwork, headers, and am just under 400hp at the wheels. it’s fun, for sure. traction is very limited and can go sideways at 45mph when you stab the loud pedal.
i think it’s a bit too much for the car, or am i too old? lol
with that said, my next project is a supercharged LS3 in my '68 AMC Rebel and 800hp goal. i have a sickness…

1 Like

I know exactly what you mean… I’ve had the sickness or “bug” as I call it since I was 18 and that was a looong time ago.

Luckily, we have lots of country highways and long roads with hills and bends that you can enjoy driving on without doing anything too dangerous or illegal.