This is what I found out about the XJ-S V12 whilst looking for a good basis for my race car, unfortunately I didn’t know all of this before I bought one! I am only looking at the UK market V12 Coupe, not cabrio or the 6 pot models.

Before going out and buying the first XJS I could find I restrained myself and did some research, which proved vital. Starting with magazines and the club web site/forum, I quickly found reams of data on everything from methods of improving the axle breathers to which model had the TWR special upgrade kit and indeed what that kit actually did.

I found the best prices for old cars can usually be found in local and free papers, fish4 trawls through all these and it is worth looking at. Ebay gives you good descriptions and is sometimes cheaper than Autotrader, though for MGBs Autotrader is the cheaper of the two, so it depends on the model. The cheapest place for cars varies depending on what type of car you are after, for example Land Rovers are cheapest in Devon, Rovers in the Midlands etc. It seems worth shopping around. But I remembered the golden rule ‘Never ever buy a car without test-driving it first’.

'To finish first, first you have to finish', never has a truer cliché been coined. Some cars are born with problems and will never be reliable; some are so sweet they are practically blueprinted. When selecting my car I looked for a sound engine that had been cared for but well used. If a car does not get used much the seals dry out and other parts seize up or corrode, a 10,000 miler that’s only ever gone to Asda may not be a good basis for a race car. I looked at more than ten cars before eventually going for the best mix of quality vs price.
A trawl on the net gave me a feel for the sorts of prices they go for, scrap for £500, useful at £2000, very nice at £6000.

The XJ-S (the hyphen was dropped in 1991) was launched in 1976 as a V12 (the 6 pot was launched in 1982 and produced in so many bewildering variations that it is beyond me to list them all, but here are the edited high lights.

Engines:

For the 5.3litre engine, the power ranged at various points in its life from 265BHP to 299 BHP. It seems most UK variants were 299bhp.
In 1980 there was a short run of engines with a slightly higher power due to the compression upping from 9:1 to 10:1, but I cant find out how much more power!
In 1981 there was a significant change in the engine with the introduction of the HE (high efficiency) engine, this had a recessed exhaust valve for massively increased swirl and a remarkably high compression ratio of 12.5:1, however power remained the same 299bhp.
In 1994 the 6.0 litre arrived with 318 bhp and more mid range torque. It also had its air filters right at the front of the engine bay where the fresh air is, the parts for this can make a useful tweak to older engines.

The flat head pre HE engines have more tuning potential because the exhaust is less shrouded and you can fit bigger valves than you can on a HE, but changing valves and cams is expensive and not allowed in the race class I have gone for.
Both HE and pre-HE engines can be tuned to give another 10% on a tight budget, so there is no real difference to me for this project. This is done with intake and exhaust mods.

Suspension:
When it came out in 76 it had a rear anti-roll bar, this was deleted when the HE came out, I have no idea why unless it was to make it under steer more for ‘safety’.
The front anti roll bar remained the same during this change.
Then, in the late 80’s, the Sports Pack came out as an option, then later as standard.
The rear spring rates were upped and the front spring lowered to drop the nose by 2 inches.
It also had a rear anti roll bar and a stiffer front anti-roll bar.
Now, if you look at the pictures from Croft circuit, you can see how much my car is rolling on standard HE springs and only a front anti-roll bar!

Differentials:
Originally it came out with either a 3.07:1 or 3.11:1 ratio diff but when the HE came out it fell to 2.88:1 so the cruising fuel economy would improve (and I have to say I get 25mpg out of mine). In so doing they ruined its acceleration.
However, the 6 pot cars had an even better 3.54:1 diff. Which is why I bought one to swap the axle over.
All of these had the PowrLok limited slip device in. Some had speedo drives on.
Most variants were made by Salisbury but the 2.88 was made by Dana, all of which ended up being owned by GKN.

Brakes:
They stayed the same other than ABS being introduced in about ’87 which necessitated wheel speed sensors being fitted to the hubs.
The most interesting change was the latest (’96?) cars having outboard rear discs a bit like the XJ40.
I am told that it is possible to fit XJ40 outboard set up to my car, but the XJ40 was metric so the hub bolt requires a bit of sleeving to make it work. So far I think I need the XJ40 hub and drive shaft to make it work.

Common problem areas:

I found out that I needed to check a few critical areas
? Rust at the rear and front end of the sills (it may be a lot worse than it looks)
? Rust on inner wing at the damper mount area (will be worse than it looks, double skinned nightmare)
? Rust where the trailing arms bolt on to the body (rust trap),
? Oil leak from crank rear seal (due to lack of use and drying out, may fail badly in a race)
? Water pump leaks and bearing looseness
? Rattles on cold start up (engine worn, expensive and time consuming to repair)
? Smoke on start up
? Smoke on overrun with hot engine
? Overheating, ask if there have been any cooling issues.
? Rusty front cross member under the radiator
? Rusty front suspension subframe
? Clonks or whines from gearbox, or burnt smelling gearbox oil.
? Check coolant, engine oil, transmission and PAS oil levels and note quality (has it been changed recently?)
? Electrical faults with ignition, fuel system or lights.
? Smell of fuel in boot (may indicate rusted vapour separator or worse, rusted tank)

I decided that if the car has any of these problems then I would walk away and look for another one.

Other common problems are less important because they will be dealt with during the conversion, these include
? Head lining sagging (its coming out!)
? Front wheel bearings (replace and use up-rated grease)
? Brake pads, flexi hoses and disks (all getting up-rated or replaced)
? Exhaust centre section blowing (it will be replaced with a piece of bent tube)
? Electrical faults with the cruise control, trip computer, clock, radio etc (all coming out)
? Belts (replace as needed)
? Tyres (race tyres go on)
? Carpets, trim damage, cosmetic blemishes.
? Slight pull on steering (if major then it’s a different story)

I decided that if the car has any of the above faults then I will talk the price down but it won’t put me off the car.

So there you have it, that’s what I learned. Not a lot really but there is oodles on the Jag lovers web site, just look at the links on my Jag home page.