Paul Mullen bought his ideal XJ-S - a rare pristine black Convertible
- then he up-graded it.

 WE PROBABLY TAKE IT FOR GRANTED NOW THAT Jaguar built its exotic V12 engine in larger numbers than any other manufacturer in automotive history and that it was created by some of the best engineering brains ever. I purchased a gorgeous 1989 XJ-S Convertible V12 in 2009 from Tony Dockerty in Melbourne. Tony was a true gentleman and known to many in Jaguar circles, but unfortunately he unexpectedly passed away late in 2013.

The XJ-S presented well, and it came with a full Jaguar service record and no modifications other than a non-genuine radiator and twin electric fans. After driving around Sydney during the Summer months, I noticed the coolant temperature would rise to about 110°C, so had it checked out at Cremorne Prestige where my good friend Greg advised that my after-after market cooling fans just weren’t up to the job. Greg maintains that the factory set-up works well provided it’s properly maintained. However, in my case, all original parts were now history so I needed to investigate an up-grade.

I set about researching the internet regarding cooling issues with the Jaguar V12 engine, and found plenty of material to read! This became the start of my journey towards a series of modifications to make my wonderful XJ-S more reliable, responsive and practical.
Any modification needed to enhance the car, and not destroy in any way the wonderful Jaguar refinement. The entire project started with the cooling system by sourcing a high performance single-pass aluminium radiator from Race Radiators in Melbourne.
The original system uses a dual-pass radiator design which I believe is not as efficient as a single pass one, so ‘while I was there’ I decided to remove the water pump with the intent of refurbishing it.

I then read an article about substituting the mechanical pump with an electric one identical to those used in many modern cars.
John Benson of Davies Craig in Melbourne has been supplying electric water pumps for years to a variety of vehicles, so I purchased the EWP 150 with the latest electronic controller. Fitting was a little challenging as I needed to make a new cover plate to replace the original mechanical pump and re-plumb it with new hoses. I mounted the EWP under the power steering pump connecting to the lower hose from the radiator, and then up to the input spigot that I fabricated on the original mechanical water pump cover.
I next fabricated a by-pass pipe between the thermostat housing. Input to the radiator is made via a new cross pipe with integrated filler neck. Davies Craig recommends removing the mechanical thermostats because the electronic controller is designed to manage the engine temperature by controlling the flow of coolant.

Because the Jaguar V12 engine needs to operate at 90°C for optimum performance, and the mechanical thermostats do a good job, I decided to retain them. With the combination of the Davies Craig EWP smart controller, and the mechanical thermostats, the engine temperature is now always at 90°C regardless of ambient temperature. Other features include fan run-on after switch off which helps reduce heat soak – which is very important and useful.
To manage the airflow through the radiator in slow traffic conditions, I installed a SPAL high performance twin 12” electric fan system which fits onto the radiator perfectly. The cooling up-grade makes for a very effective and reliable modification, and I now have no issues driving around Sydney on 30°C plus days. Never under estimate the importance of running the V12 at the correct temperature. If it gets too hot you will cook the engine, while too cold could result in over fuelling.

The next modification was aimed to improve the responsiveness and flexibility of the engine without destroying the original Jaguar refinement. I started by replacing the ECU with a re-mapped unit purchased from AJ6 Engineering in the UK. I also installed their larger throttle bodies and high torque manifolds, achieving better air flow to the cylinders. Cool air is directed to the intakes from the front of the radiator.
In order to install the new ducting, I replaced the bonnet from a six cylinder 3.6 XJ-S which has the higher bulge. It is the same type of bonnet fitted to the later cars with the factory installed 6.0 litre engine. I complimented the induction system with AJ6 Engineering’s high performance exhaust kit. Roger Bywater from AJ6 Engineering says: “Many people think that the exhaust system on a modern Jaguar is a little too quiet for a car with high performance pretention, and it is quite possible to obtain a reasonable increase in performance allied to a pleasing exhaust note without becoming an antisocial monster”. While this all generates more bhp, I wanted and achieved a more responsive engine with a hint of that enjoyable high performance sound.
I read a lot of articles about V12 engine under-bonnet fires, and really didn’t want to experience one! I therefore had a set of aluminium fuel rails fabricated by Ed Ward in Melbourne. It seems most of the Jaguar expertise resides in Melbourne!
These fuel rails are manufactured from extruded aluminium, and eliminate the horrible clip-on rubber hose design of the factory unit. I replaced the injectors with a set from the XJ-S 3.6 which has a similar flow rate. The end result is a much tidier engine valley.
The second stage of the modification was to install a Wolf Engine Management System to provide sequential ignition and fuel injection. This will involve replacing the ignition system with a distributorless ignition and more modern high flow injectors, a complex up-grade and will require considerable planning and patience. The nett result should deliver more simplified engine control. Ian Hissey has carried out this up-grade, and many other clever modifications to his well known XJ-S Cabriolet and has valuable information on his website www.ichi-intl.com.au.

All XJ-S V12s manufactured before 1992 had the GM T400 three speed auto transmission, but I really wanted an extra ratio to help with fuel economy and improved responsiveness. To that end I installed the GM T-700 transmission, with a conversion kit from John’s Cars in the USA. The job was relatively straight forward provided you follow John’s instructions to the letter!
I sourced a T-700 from a 1990 Holden Commodore, and had it rebuilt by a local transmission shop. I also installed a dedicated low-profile transmission cooler in front of the air-conditioner condenser. The original prop-shaft needed shortening, so John’s Cars supplied on exchange. In order to get the best out of the T-700, I changed the diff ratio from 2.88:1 to 2.54:1. The combined modification made a real difference to the car, and I don’t understand why Jaguar didn’t do it earlier.

The XJ-S steering and suspension has to be one of the best designs ever, coupled with the amazing independent rear suspension set up. Nothing here needed changing other than an up-grade to poly bushes and adjustable Monroe shock absorbers. However, when setting up the wheel alignment I opted for more positive caster due to the wider tyres and wheels I fitted. I installed 16 X 8 XJR-S Sport wheels which set the car apart from the standard model. Brakes are all stock and seem more than adequate for the job.
The electrics in the XJ-S after twenty years of use had become somewhat unreliable, so I set about replacing most of the wiring, particularly in and around the engine bay. I purchased a four headlamp kit from SNG Barrett in the UK which I modified for projector lenses sourced from a BMW 5-Series. I then installed HID lights which dramatically improved the overall lighting. Other electrical changes included wiring and relays for the cooling fans, horn, lights, air-conditioning and others.

The air-conditioning was up-graded to include a modern new lighter-weight compressor from SC Parts in the UK. I also replaced the condenser with a parallel flow unit, and the result is ice cold air-conditioning in the summer.

Internally, I had it re-trimmed and carpeted. The wood veneer was replaced with new Burr Walnut from Myrtle Productions in the UK who also manufactured a custom dash surround which is similar to the dash on the Facelift XJ-S. This dash surround uses the original speedometer and tachometer, but smaller gauges from the Series 3 XJ saloon. I changed all the gauge lights to LED which provide a more modern look at night. The result is a smart looking centre dash console which blends well with the rest of the interior. A new Alpine stereo system finishes it off with Bluetooth phone interface.

My XJ-S is now a real pleasure to drive, and I never think twice about making the long trip from the Southern Highlands to Sydney.

Article Courtesy of: EDITION 178 JAGUAR MAGAZINE