Gents,

The much unloved XJ40 body style prices are in the toilets. I've seen some complete XJ12s with relatively low miles going for lunch money. Has anyone transplanted the V12 and 4 speed transmission into an earlier XJS? Is it a massive undertaking? How much Jaguar mechanic time and custom fabrication are we looking at?

I'm thinking the HP bump from 262 to 318? plus the 4 speed transmission would be nice. Any thoughts?

Thanks

 

I am in the process of exactly that at the moment. Car is in for paint in a couple of weeks and then engine/ trans will go in.
Trans has been trial fitted after slight modification to the oil pan to allow it to fit rather than modify the tunnel of the car. It is my intention to return the car to original matching numbers and I did not want to permanently alter anything body wise.
Trans controlled by EZ-TCU aftermarket computer.

 

Flint Ironstag,

I'm sure it can be done with enough effort. There are some things that you need to consider. Although roughly the same, the XJ40 6 litre has some differences to the XJS 6 litre. It uses a different ecu and I think that either the aircon compressor or alternator are in different places. You may need a lot of bits from a scrapped 6 litre XJS to make it fit properly. I might know where is one of these, so drop me a line if you need to know.

Good luck

Paul

 

If you are going to do it why not stick a manual box in then you can fully use the potential of the engine?

 

Cost?

 

Fair enough.

 

I am also in the middle of the same swap. Putting a 94 xj12 6.0 into my 90 xjs convert, check out my Flickr page. At this point I have the 90 engine out and completely rebuilt the entire front suspension. I am a few weeks out from taking out the 6.0. My plan is to put the xj12 engine and trans into the car and I am upgrading the rear end to 3.54 gears so I don't mess us the transmission shift points. My observations so far is that I will be swapping some of the 90 xjs engine parts onto the 6.0.

The list of parts I know I need to swap are as follows:
Coolant crossover pipe
The power steering pump and Air pump are on opposite sides between the two cars
A/c compressor
Harmonic balancer due to 4 ribbed pully vs 1 rib pulley on ac compressor
Water pump and fan pulley. Although I am going to go to electric fans.

The list probably has a few more I haven't come across yet

 

I have an XJ40 6.0L now in bits, it will bolt in directly.

There are some differences but these are minor, mine is from a LHD car so the throttle capstan cable is on the wrong side. AC, alternator PS pump all the same position. The AC compressor mount is different and the old A6 compressor will not fit, so good excuse to upgrade that.

The XJ40 also does not have the radiator cap on the Xover pipe but your XJS pipe will fit.

 

@baxtor

What did you use to mount the transmission to the car. The original 5.3 trans mount or did you have to get a 6.0 xjs trans mount assembly. Where you able to reuse the 5.3 driveshaft as well. These are my only two concerns at this point, that I haven't figured out the answer

My xjs has the speedo pickup in the diff so my speedo will work with the 4l80e trans attached to the 6.0.

I know the engine oil pan on the 6.0 xj12 and the xjs is different so I will be swapping those as well. What does the trans oil pan interfere with to cause you to have to modify either the pan or trans tunnel? Do you have any pictures?

Thanks!

Scott

 

I am using the 6.0 litre XJS rear mount, straight swap uses existing bolt holes and position is correct. Drive shaft needs shortening by 78mm from memory.
the oil pans are different but I am sure it makes no difference.
Have attached a couple of pics which show the trans.case mods and fit issues. I am sure you could modify the tunnel without much effort but in my own case running the 6.0/4L80E is only while I rebuild the 5.3/T400 and it allows me to take my time while still driving the Jag.

 

I have confirmed that the 4l80e is 3" longer than the turbo 400. I am waiting to get my modified driveshaft back. I could have used any facelift driveshaft as they are the correct length as well.

I purchased a new XJS 6.0 trans mount CCC4507 as my xj12 mount is completly different. However I was able to reuse the spring and purchased a new bushing MMC 7553AA. It is pretty awesome that the car has the boltholes already in the body for the 6.0 mount. Mine were sitting there completely unused. Thanks Baxter that info saved me a ton of fab time.

I am going to massage out the trans hump if needed instead of modding the trans. I am just waiting on my swaintech coated exhaust manifolds and then I will be putting the motor in the car.

 

Update: I completely removed the 5.3 T400 trans mount and was able to mount the 6.0 and 4l80e without modification to the trans tunnel or transmission.

 

After getting some miles up on mine I found the gearbox did on occasion make light but annoying contact with the tunnel on the rebound of the rear mount spring on uneven sections of road. (that was a mouthful) I slipped an 8mm aluminium spacer between the rear mount and body rail each side and that has refined the whole setup.
Same result could be had just playing with the rear mount spring options.
The end result of the swap is chalk and cheese, particularly the gearbox change, I am sure you will love it.

 

Baxter: Can you share how you hooked up the electrical side of your 6.0 swapped car: which wire harness was used, which ecu, which tcu, any custom work necessary. My understanding so far is you are using the TCI EZ-TCU. Any advice is welcome and I hope you are enjoying your car.

Thanks!

-Scott

 

Scott,
All wiring and ecu's remained stock '89 marelli. Entire fuel system is the original 5.3 set-up with a Bywater re-chip and slight fuel pressure increase to his instruction.
Gearbox ecu is TCI ez-tcu which I am very happy with. It seems to be very user friendly and adjustable to personal taste. TCI actually states that the V12 is not supported but so long as you are running the Marelli ignition the set-up is essentially a 6 cylinder anyway.
Mounting of TCU shown, RH drive car. Only engine bay wires are main earth and live to firewall posts, one wire to piggyback throttle pot and one engine speed wire to diagnostic plug coil feed via supplied sender unit.
Very happy with the outcome. I ran a series Ixj12 with manual box for many years and I actually prefer the 4L80E.

 

Hi 86jag,

Were You able to finsih the procect? Did it work? I am working actually on the same conversion. Could You give me an idea where I could get a rear gearbox mounting bracket CCC4507?

Thanks, Johann