XJC.COM.AU - Ian Duncan's Coupe Story

  The Website dedicated to the XJC -
  Jaguar and Daimler XJ Coupes


Ian Duncan - My Coupe  - 1977 Jaguar 4.2C

Modernising an XJC.

“Hope springs eternal in the human breast: Man never is, but always to be Blest”.

Alexander Pope probably wasn’t thinking of car restoration when he coined this phrase in the early 18th century, however it does seem to fit remarkably well –  particularly when you want to modify as well.

Click on pictures below for a larger view.


 

After 4 years of effort, I felt the urge to let other people know about this project, however was keen to avoid writing yet another restoration chronicle – there are many others out there more comprehensive and interesting than anything I might write. It did cross my mind however, that others might be interested to read about the rationale behind the restoration, and some of the details of modifications made along the way.

People have varying attitudes to living with an old car. Some will buy a good original car and do their best to keep it that way, while others will buy a cheaper car and deal with problems as they arise. I don’t enjoy having a car with obvious blemishes, and so a complete strip down, bare-metal body restoration, all mechanicals, interior and trim was always part of the plan. One of the benefits of this policy, as I found out previously by restoring and then using a S1 XJ6 over 14 years, is you end up with a car that is very reliable in the long term.  And the downside ? - $$$. In addition to restoration, some modifications were planned, mainly with a view to making the car more useable.

The car is a 1977 XJC 4.2. Original colours were Squadron Blue and Cinnamon interior – surely one of the better combinations in the late 70s? I am the 4th owner, and bought it in a sorry state as a restoration project. It was fitted with a 350 Chev that ran like a pig (don’t they all?), and a T400 auto. Body and interior were reasonably original, and there were a few bonuses - the seats had recently been recovered, and a few spares were included such as a set of new body rubbers.

 

Before...

After...


 


Perhaps the 1st question is why choose an XJC ? Firstly, while quite a complex car to restore, they share 95% of their components with conventional S2 XJs, and so most parts availability is not a problem. Secondly, an XJC is quite a practical and ‘liveable’ car - you can fit adults in the back seat; they came standard with a reasonably effective climate control system and power steering; and they offer levels of quiet and smoothness that compares well with modern cars. Finally, XJCs have that combination of rarity, aesthetics, and performance that make them a very appealing car by most standards.

One of the objectives of this exercise was to end up with a car that could serve as the 2nd family car. As such the potential maintenance and running costs of a V12 were a big factor in favour of looking for a 6.

 

One of the worst things about Jaguars is that most of them have old-man’s gearboxes. My previous S1 was a manual overdrive, and it was only the temperamental and fragile overdrive – particularly behind a warmed up 4.2 XK - that decided me to go for a 5 speed conversion instead.

The engine was another item to receive attention. The V8 was installed into the S1, and with a bit of detailed tuning it still ran like a pig, albeit quite a smooth, grunty and very thirsty pig. The 4.2 originally from the S1 had been comprehensively re-built in the mid 1990s, and had done 50,000 careful kms since, running on $12/litre synthetic oil.


XK is huge compared to a small block Chev

 

More due to personal interest and the ‘why not’ factor than due to cold reasoning, conversion to fuel injection and electronic ignition was another part of the plan. This is opening a big drawer in Pandora’s box, however, as there are many ways you can go about doing this, and fitting a system from a S3 while simplest, is certainly not the only option.

The option chosen was to fit modern sensors and a digital engine management system. Doing a modified system required some effort. Aside from the research and assessment of various options, a number of adaptor and cover plates had to be designed and manufactured for the inlet manifold, a S3 distributor had to be modified to suit externally controlled ignition advance, an amplifier that suited the inductive pickup in the distributor had to be sourced, however probably the most difficult job was making up a wiring loom and grafting all the new electrics into the existing electrics. The result is essentially a Jaguar manifold and injectors, with a GM digital engine management system, throttle body, ignition and sensors. In this later regard it most resembles a VN - VT 5.0L Commodore.

 

Standard S3 XK engine with Bosch L-Jetronic EFI
1. Water-heated throttle body.
2. Over-run valve and air idle assembly.
3. Cold start injector.
4. B-metal cold-start air valve.
5. Coolant rail with thermo-time and coolant temp sensors.
6. Ignition amplifier (front of manifold).
Missing: flap/spring type air flow meter.
Modified XK with Digital EFI
1. 65mm throttle body with air idle sensor (IAC) motor/valve and throttle pos sensor (TPS) - (VN to VT 5.0L Commodore).
2. Manifold air temp (MAT) sensor. 
3. Coolant temp sensor.
4. Ignition amplifier/interface unit. 1.8/2.0l Camira, Pulsar, Astra etc (front of manifold).
Missing: Manifold Air Pressure (MAP) sensor, fixed timing distributor (vacuum and centrifugal advance mechanisms disabled) and exhaust (oxygen) sensor.
 

Two other changes were made to the engine, both sourced from AJ6 Engineering in the UK. The first is a modified inlet manifold, designed to provide ram-forced induction. Most modern engines make use of this, whereby having sufficient length in the inlet ram tubes allows pressure pulsations as the inlet valves actuate to assist with drawing in the inlet charge over a limited rev range. Many modern engines have variable length intakes to spread the effective range. It can be considered the inlet equivalent of exhaust extractors 

The 2nd modification was a 304 grade stainless steel exhaust, with 2 key differences from a standard system. Firstly, no mufflers are used prior to the axle overpipes, and secondly the engine pipes are considerably extended before joining. Pipe diameter is standard 1.75” 

AJ6 engineering claim that the use of this exhaust system and inlet manifold considerably enhances mid-range torque. And they should know – Roger Bywater worked with Trevor Crisp at Jaguar in the mid to late 70’s developing the EFI version of the XK engine, as well as doing development work on the V12 and AJ6 engines. AJ6’s website is definitely worth a visit.

It is all very well to research and go to this trouble, however was it worth the effort? As the biased owner, I am probably the last person who should comment, however, for what its worth, my assessment is as follows:-


View through throttle body hole of extended ram tubes.


Stainless steel exhaust system.


Ease of use – The engine is definitely much smoother, with none of the idiosyncrasies when cold that the SUs had. Starting, cold hill-starts, throttle response and cold exhaust smell are all on par with a modern car.

Go – Peak power levels tell only a small part of the story, however I am advised that an everyday carb’d 4.2 will produce 80-90 rear wheel hp on a rolling road, and a triple SU, manual car might deliver 110-120hp. I have seen a good V12 HE XJS plot showing 168 hp. As such the 140 we achieved is pretty good. When you look at the plot however, it can be seen torque drops away from 3700 rev/min, and the power plot is pretty well flat from 4000 rev/min. Possibly the cold-air intake is causing a higher speed restriction that is robbing maybe 20hp. On the road the car feels responsive with loads of mid-range torque. Higher speed performance is impressive – 2500 rev/min in 5th equates to 115 km/hr, and acceleration at these speeds in 5th feels stronger than the 350 Chev, which is doing more like 2800 rev/min.

Fuel consumption – Each of the tanks hold ~ 42 litres when filled with the gauge showing empty. The car will do ~ 375km of freeway driving from a tank, and I’ve not seen < 300km for local running around. 

Mechanical work and modifications were only part of the story with restoring this car. Other modifications included re-bushing the front suspension and steering rack with polyurethane, and fitting Koni shock absorbers all round. Fairly substantial changes were made to the air-conditioning system, by scrapping all the original electronic controls and servo mechanism, and replacing them with pneumatic valves and actuators, a microcontroller, and a little LCD screen that sits just below the centre air-outlet.



Chassis Dyno Report


At the 2007 JDCA concours (Greg Jones ex multi-award winning coupe in the background)

 

The final act to the story was I kidded myself into thinking the restored car might be good enough to enter into a concours. So I took some time off and spent a solid week or so cleaning, polishing, touching up underbody parts (the car had done ~ 5000km since restoration), and had the paint polished. I was quite surprised, and very gratified to pick up a Gold award at the 2007 JDCA concours for my efforts – clearly a few others had been kidded as well!