De-mystifying the Jaguar V12

The Jaguar V12 engine is one of the greatest iconic powerplants ever made, powering the E Type, XJ12 and XJ-S models plus numerous successful race cars from Touring Cars to LeMans GTs. But for some the apparent complexity makes it a very scary option. Having raced these magnificent units I feel it’s time to set the record straight.

Looks simple enough....

The first time I opened the bonnet on my XJ-S V12 I just stared at it in disbelief for a few minuets, then gently shut the bonnet again and walked away. To say it was full would be an understatement, it looked like someone had emptied a very large bucket of automotive spaghetti into the engine bay until it was full, then smoothed it off with a very big oily trowel.
Which is a very great shame, because the engine itself is a fairly straight forward design, just with 12 of everything. Owning and driving one is a fantastic pleasure, round town the engine is silent from within the cabin and it is arguably more refined than a Rolls. On the open road it has a briskness that defies its size, and given enough space has a relentless thrust that just keeps on going.
So if you have a desire to own one then don’t let the tales of woe put you off. It is only that the parts bolted on to the engine, such as the fuel system, air control system and electrics that seem shockingly complex, and that is only until you get the hang of what does what.
The good news is that the engine itself is very reliable and can cope with a huge amount of abuse, the bad news is that because of this many older cars have many missed services, giving the new owner quite a lot to do. The base engine has gone through three main changes over the years; the original E Type and XJ engine had flat cylinder heads and is the one preferred by the racing fraternity, but it had an alarming thirst for fuel. The fuel crisis of the 70’s led to the High Efficiency HE engine, introduced in the early 80’s, with a very high compression ratio and very special combustion chambers with a heavily recessed intake valve for very high swirl rates, this limits tuning potential slightly but gives amazingly reasonable fuel consumption, I used to achieve about 25mpg on a run from my XJ-S HE. The HE stayed in production into the 90’s when it was replaced by the 6 litre bock which was largely the same but with a longer stroke.
All these engines are very robust, as they are derived from the XJ13 race engine the 5.3 revs to 6500rpm and the 6 litre goes to 6000rpm. Because they are designed to be quite happy running at these speeds, in an every day road car they are totally unstressed. Of course this pedigree means it is still great for classic racing today, many racers take engines straight out of scrap cars and merely change the oil before heading for the track.
Speaking of oil, it does take quite a lot of the slippery stuff, over 10 litres is usual making an oil change a substantial investment. The oil tends to last quite well however, an oil cooler is standard and the engine’s quick warm up system minimises oil contamination. When changing the oil it is best done with warm oil, as with most engines, but leave the exhaust for a while to cool down because the oil filter is right next to the down pipes and contact is inevitable.
The simplest incarnation was in the carburettor fed E Type and XJ12 models, but the engine was designed for fuel injection from the start, and as soon as a suitable system was available it was fitted to the XJ12, the XJ-S was injected from the start. The systems was very sophisticated with little extra features to enhance performance and emissions, all stacked on top of the engine, making it look so complicated. Breaking it down a bit, there are six main systems in that spaghetti; fuel, vacuum, engine management, ignition, cooling system and air con.
I will take a typical S3 XJ12 as an example, then go over differences on other models later. Opening the bonnet reveals a network of small bore tubing, some of this is the fuel system with the U shaped fuel rail feeding all 12 injectors, but most of the small tubing is the complex vacuum operated control system for the distributor. The front of the engine is dominated by the air con pump with its cylindrical silencer, yes that’s right the air con pump has a silencer, very refined.
You will also notice it has two cooling system pressure caps, one at the front of the engine and one on the expansion bottle on the wing. Nearer the rear of the engine is the throttle pedastle, this is where the throttle cable operates a circular device that in turn operates the two throttle links, more of that later.

With a gearbox on its over 7 foot long and weighs half a ton

Lets start with a potted history of the ignition system, it has gone through several major changes over the years, most models of the 70’s and 80’s use the 12 cylinder Lucas Opus distributor, similar to many other BL cars of the time. The HE engine’s high compression ratio required much more spark energy at high speed than the older engines, and feeding a spark to 12 cylinders at engine speeds up to 6500rpm require the coil to store a lot of energy, it was too big a job for just one coil back in those days so the cunning chaps at Jaguar doubled up the coils, one coil has the king lead to the dizzy and the other sharing only the low tension 12v side of things. This secondary coil looks a bit odd, as the king lead post is blocked off, the main coil is located next to the dizzy but the secondary coil is mounted right at the front of the car, in front of the radiator, if its faulty or missing then the engine will misfire at high rpm but may well run perfectly round town.
Later models managed to use just one, more modern, coil. But when computerized mapped ignition was installed the need to have the coil towers further apart required a novel system from Mirelli which effectively incorporated two 6 cylinder distributors in one, stacked one on top of the other in the same housing. This system has two coils next to the distributor and two king leads feeding a split level rotor arm.
The final iteration of the V12 ignition saga happened after the change to 6 litres when the distributor was deleted in the and replaced with individual coils for each cylinder.
Of these systems the most common is the Opus, and it is also the one with the most complicated vacuum advance system ever made. Its also very clever. To get the best from an engine the ignition advance must adapt to all engine operating conditions, a simple vacuum advance system is a big compromise but back in the 70’s full computer controlled mapped ignition was not an option for mass production. So the vacuum capsule is connected to several air solenoids, a vacuum regulator, a vacuum dump valve. The biggest problem with this comes from old rubber hoses perishing, the second biggest problem comes from people re-assembling the system incorrectly. One of the clever things the system does is warm the engine up quickly, and its huge amount of coolant. The ignition is retarded when cold and extra air is let in via an air solenoid, this is controlled by its own little electronic box of tricks which has been known to go wrong resulting in lost power and idle problems, but when it works it works very well. To compensate for lost power when running so retarded extra air is let into the manifolds by yet another solenoid. It is possible to remove this system completely, the only down side being longer warm up times.
One of the popular horror stories about this engine is that the spark plugs are impossible to change without a major engine strip down. Well, in fact most of them are no problem at all, but the front two are very close to the air con pump, a special tool is recommended but another option is to undo the pump belt and mountings and ease it over, without damaging the hoses, to get enough access.
Because of this difficulty it is quite common for the plugs to be left in far too long and start to corrode in place, so its worth blowing all the dirt out of the plug recess and allowing some penetrating oil to soak in before attempting removal. In fact it is quite important to blow any detritus out of the way first, the plugs are ate the top of the engine and it is easy for debris to accidentally fall down the hole during the change. Make sure you get the right plugs too, there was a change of design to taper seats when the HE engine came in.
The electrical system design also laughs in the face of convention. The fuel injection control really was cutting edge and in some ways daring. The early, pre-HE, ECU was relatively simple but very good at its job, the HE ECU is more sophisticated and has a manifold pressure sensor built in to the box. Unusually the ECU is mounted in the boot and the wiring for the injectors and sensors passes through the rear bulkhead and takes a tortuous route through the interior and finally emerges through the front bulkhead from whence it sprawls over the engine and wing edges to meet the control relays mounted on top of the radiator. The HE system also has a vacuum hose from the intake manifold going all the way back to the ECU. Obviously there is the potential for older cars wiring or vacuum hose to have expired in some way. Electrical connections are prone to corrosion which can usually be removed reasonably easily, but sometimes it works out easier to fit new connectors. The vacuum hose is worth replacing if its older than a decade.
The throttles, one on each intake manifold for injected engines and four on carb versions, are operated via a centrally mounted disc which is pulled round against a spring by the throttle cable, this disc also operates the load cable for the auto box and the cruse control, it also has a switch on some models for the auto box kick down and the throttle potentiometer for the ECU. So all in all its a complicated part, but all you usually need to do to it is check that the throttles all start to open at the same point, if they are a little out of balance the engine might only be using half its cylinders as you cruse round town, luckily its a simple operation involving undoing the lock nuts and winding the links in or out as described in the service manual.
The fuel system is quite remarkable too; on the XJ-S there is a fuel pump in the boot sitting in its own little tank, fed by gravity from the main tank. On XJ12 there are two main fuel tanks which both feed the fuel pump in the boot but with fuel solenoids to select which tank is used. The excess fuel returns from the engine to the tank, but because the fuel picks up so much heat in the massive engine bay it goes through a small cylindrical fuel cooler that is plumbed into the air con return pipe.
Early systems suffered from hot re-start problems due to having very small bore fuel rails which are prone to fuel vaporisation in the heat, the later larger bore system is a useful upgrade. When the returning fuel gets to the tank it goes into a pipe in the main tank which in turn goes back into the pump tank, that way returning fuel is mainly pumped straight back to the engine and the main fuel tank temperature doesn’t rise too much. This is all done to stop fuel evaporating, which became part of the emissions regulations in the 70’s, instead of the tank just venting to the atmosphere it vents into a can, tucked up into the right hand buttress on XJ-Ss and one on each rear pillar on XJ12s, which allows the vapour to condense and return back to the tank via yet another small bore pipe, determined gases are allowed to escape via a restricted pipe on the top of the canister which goes to the engine intake.
Needless to say its a very complicated system and is prone to problems, one of which is a strong smell of fuel in the cabin. Some owners rip the whole vent system out and replace it with conventional vent pipes.
Later models supplement this vent system with a carbon canister in the engine bay which absorbs fuel vapour and is emptied into the engine intake during part throttle running, ensuring the vapour is burnt and never vented to atmosphere. This is controlled by the engine ECU via a solenoid in the pipe from the canister to the intake.
Although all this pipework looks intimidating initially, all you really need to do is keep the hoses in good order, and if you are so inclined the system can be simplified and most of the plumbing removed.
The cooling system is another stunning work of art. Each cylinder head has an externally mounted coolant manifold with a thermostat and top hose at the end, in the E Type both top hoses go forward to the radiator, which was the traditional sort with a tank at the top and the bottom and the cores running vertically so the two top hoses went straight into the top tank, relatively simple compared to what happened next.
On XJ models it got a lot more complicated, a more modern radiator with horizontal flow and a separate expansion tank is used for greater efficiency and lower bonnet lines, and with a tank ate each side it made connecting the two top hoses a bit more tricky. The solution was to put a baffle plate one third of the way down the left hand tank, effectively splitting the radiator in two. The left top hose goes to the top of the left tank and the coolant then flows across the top third of the radiator into the right hand tank where it is joined by the right hand top hose. Then the mixed coolant from both heads goes back to the lower left hand tank via the lower two thirds of the radiator. Still keeping up? The bottom hose is attached slightly above the bottom of the lower left hand tank, and then feeds back into the water pump.
To make this set up work a small bore hose connects the top of the radiator to the expansion tank, mounted at the side of the engine bay. This tank feeds back to the radiator via a bigger hose at the bottom. It also supports one of the hoses for the interior heater, the other coming from the back of the right hand cylinder head coolant manifold. At the top of the tank is a pressure cap, but because this is not the lowest point in the system it should not be used to check the coolant level.
Amazingly it gets more complicated, between the two thermostat housings is a balancing tube which supports a second pressure cap, it is here that you should check the coolant level.
If you make the mistake of opening both pressure caps then coolant will drain from the top of the engine into the expansion tank and spill out. The highest point in the system is the interior heater matrix, so when refilling the coolant after a change it is best to have the front of the car raised a bit. You wont be able to get all the coolant in in one go, the trick is to run the engine with the heating on full and give it a few revs briefly then switch off and magically you can get the rest in.
Bizarrely the standard service schedule specifies dropping two pots of Barrs leaks with every coolant change, probably due the the huge number of joints in the system. This can lead to clogging in some of the coolant galleries and the interior heater matrix, so a good flushing can be helpful, and as ever old rubber hoses should be renewed every ten years or so.
Although this set up is genuinely complicated, all that is needed is normal maintenance such as coolant changes and checking for leaks, so don’t let it scare you off.
The front of the engine sports four belts on most models, and again although it looks complicated it really isn’t. at the back is the alternator belt, tensioned by moving the alternator, then there air con drive belt which is tensioned by a high mounted idler pulley, next we find the belt that drives the water pump and power steering pump tensioned by moving the PAS pump, lastly there is a fan belt with its own little tensioner pulley.

So there you have it, a glorious engine hidden under a complicated dressing. Although there are many neglected examples around, with some careful attention going through each system a stage at a time will ensure many happy years of sheer motoring joy.

About Ralph Hosier

I love exploring everything the world has to offer, the fabulous beauty and intricacies of nature, the stunning majesty and grandeur of the universe, and the fascinating range of chocolates available from the local sweety shop. I have led a charmed life, sure there has been extremes, but the highs far outweigh the lows. I get paid for arsing about in very fast cars, I get to write about them and amazingly get paid for this too. My days are usually filled by making prototype and concept cars for car companies, a dream job. I have lived many of my dreams, worked all over the world, raced cars built by my own hand (and hardly ever crashed really badly), seen things and done stuff. But nothing compares to the love of Diana and my son Peter, beyond my greatest hopes. I am a chartered engineer, a member of the Institute of the Motor Industry (IMI), and of the Institute of Engineering and Technology (IET) and I am a member of the Guild of Motoring Writers. A pleasing fact is that there are now more letters after my name than there are in it ;) R.Hosier B.Eng(Hons) C.Eng MIET MIMI MGoMW
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75 Responses to De-mystifying the Jaguar V12

  1. Ryan says:

    Excellent article! I have an XJS, and this really helped me understand things better. Is there a good resource for diagrams?

    • Ralph Hosier says:

      Thanks, much appreciated.
      There is lots of info on line, I found the AJ6 Engineering web site very informative, and the forums on the Jaguar Enthusiasts Club are great. Also look at the JagLovers web site which has downloadable books for free.

  2. Eli says:

    Nice article.
    Curious if anyone has adapted later fuel injection and coil on plug ignition on one of these beasts. Love the idea of a v12 project car but it seems like with todays tech there should be a better way.

    • Ralph Hosier says:

      The last run of V12s had distributor-less ignition and Zytek injection, these went in the facelift XJS and X300 XJ12 cars. There are also bolt on conversions, often using two ECUs with each one doing one bank of six cylinders. This works very well and is great for getting every last drop of performance out of that magnificent engine.

  3. Dan Sater says:

    Ralph thanks so much! Great information. Now I understand a little better why my Jag mechanic cringes when I come in with my XJS!

  4. Mark O'Baldwin says:

    The exhaust valve is the deeply recessed one in the H.E. heads, not the intake. It’s “Marelli,” not “Mirelli.” But aside from those minor details, a tidy & informative piece; thanks!

  5. keith Groves says:

    Ralph, I reckon this is the best written article on the V12 I have read, and I think I have read them all. I am building a replica Ferrari Daytona and putting a Jag Engine in it. I currently have an early Etype V12 but intend to put a 6.0 L in when I find one, my intention is scrap all the std injection and ignition and source modern equivalent …. any suggestion for a complete set up from scratch, cost is not a concern cos I am never going to sell the car.. I intend to make it the best it can be I am also looking for a good manual box to go on it thought of using a Tremec any thoughts…..
    Again great write up……… Regards Keith Groves

    • Ralph Hosier says:

      Most bolt on ecu systems only cater for us to 8 cylinders, so you may have to double up and run it as two straight sixes, which has been done many times in the past. There is a steady flow of new ecus turning up these days so it’s worth ringing round and finding the best one. The stock engine is good for over 6500rpm, race engines can go to 8000! Times that by twelve cylinders and you need a fairly meaty ecu to do it justice. Have a word with the guys at AJ6 Engineering first, but what ever system you use make sure there is local support. Sounds like a great project, all the very best of luck to you.

      • keith Groves says:

        I know the guys at AJ6, and have spoken to most of the systems manufactures I can find in UK and the US and offered to be a distributor for a couple in the US. I have found several examples of systems that have put together from various components (and as you say 2×6 in parallel) but not a fully integrated system when I complete mine I thought I would document it and maybe offer it as a complete system.
        I come from a similar background to you except I did a PhD in Physics at Brunel and then studied Metallurgy Charded Engineer and worked for ESA on the Hubble and few other interesting programmes then moved into Programme Management. When I finished Uni I was by pure accident offered a job at Mclaren by Ron Dennis but did not know who he was, nor that I was in the Mclaren Workshops because I was in the back of the workshop and there were no cars nor indication thereof.. so turned it down..
        c’est la gare
        I’m sort of retiring now and intend to play with my cars and bikes only had to wait 30 years LOL

      • Ralph Hosier says:

        Sounds great, you’ll have to keep us posted on developments!

    • Ian Giles says:

      Very interested to hear you are building a Ferrari Daytona replica. Have you contacted the Daytona Replica Club? We all have these cars and the guys who built their own have a wealth of experience they would be very willing to share with you.
      Ian Giles

  6. Michael Coffey says:

    Thanks for a very good article I have a 1984 XJSC it was running very well a few months ago but due to circumstances it was left idle for a couple of months I’ve got a new battery on it the engine turns over but will not fire any ideas.

    • Ralph Hosier says:

      Well, could be a number of things really! First do the usual of checking for spark and fuel. Usually wiring connections suffer when a car is laid up so check the ignition system is getting power, ground and a good trigger signal. Check the ECU connections and check that the injectors are firing. Check for fuel pressure, pumps can stick due to old fuel and can sometimes be jolted back to life with a gentle tap or briefly running them with the power reversed. Also check the distributor cap, sometimes moisture condenses in there causing problems.
      Best of luck.
      And thanks for reading.

      • lewis price says:

        can you help? I ave a lovely v12 etype roadster which although runs very well I can hear a loud tappet noise this is the 4th etype I have owned and cannot say I have heard this before what is the remedy? thank you Lewis

      • Ralph Hosier says:

        All I can relate is my own experience. I did have a V12 that made a tappety noise, that engine had been started briefly every month to keep it working but had not been driven any distance for about a year, turned out one of the cam followers was just sticking slightly due to lack of use. An oil change and a good long drive fixed that one.
        I don’t know if yours has the same issue, of course there is always the possibility of some small mechanical failure so it may be worth taking it to an expert locally just to be sure.

      • lewis price says:

        Thank you I will try the oil change and long drive and see what happens . The other question is I have found small amounts of oil on my garage floor and although it doesn’t appear to be from the engine but sort of from the centre of the jag . the whole of the engine was rebuilt some 8yrs ago and has only covered 5k miles since could this be the crankcase and is the only solution to cure this being a costly engine removal? What would be the consequences if it was not topped up with oil.Lewis

      • Ralph Hosier says:

        Could it be the gearbox sump gasket? All my old jags leaked a bit, old seals and gaskets harden and fluids seep. You could just keep checking and topping up the engine and gearbox oils. Might be worth changing the gearbox and engine sump gaskets which is easy and should be reasonably cheap. Might be worth checking the rear crank real too which hardens he the car is not used often. Also the cam cover gaskets can leak, the oil tracks down the gearbox and drips from the middle of the car, again reasonably easy to change.

      • lewis price says:

        Thanks I will check them all out and hope for the best. Lewis

        ======================================== Message Received: Jul 18 2013, 11:15 PM

  7. David Cox says:

    Liked the article… and am trying to figure out my 1986 XJSC V-12. It had been acting like there was a brake problem after driving it for about 5 minutes. If you turned off the car, walked away, and then came back in 10 you could drive it all day without problem. Took it to Meineke to see if there was a problem with the brakes. Brakes are about 50 % all around.

    When I got it to Meineke before it went in it lost some coolant, but they were unable to figure out the Jag and after checking the brakes didn’t want to mess with it. I drove it back home, but on the way after 2 miles I started to get a sound that reminded me of a lifter going out. Oil was up fine. I thought I might take it to a shop that works on older imports… but wonder if there is a coolant issue with one of the cylinders after reading your article. I was thinking about getting the vehicle new spark plugs and tuned… and have them check the coolant system if they think they can examine it…

    Am I at least thinking in terms of the right direction?

    • Ralph Hosier says:

      Those old motors have so many parts and systems it is notoriously difficult to diagnose remotely. If yours has the cold start ignition retard device, that speeds up warm up, that might be sticking which robs all the power. Chances are that it may be some of the small vacuum tubes that control the whole thing, they perish and leak after about ten years causing all sorts of problems. But as ever it could be something else.
      So I would look at all the small tubes, check they are all connected the right way and not damaged, then give it a full service including all the plugs and check the distributor cap and rotor for carbon build up.
      By the way, the only way I found to get all the air locks out of the cooling system was to jack the back of the car up about three feet so the engine is tilted forwards! If there is an air lock then it tends to blow a little coolant out of one of the pressure caps just before the thermostats open.
      If you’re loosing coolant but its not dripping on the floor then it might have a head gasket leak, although this is quite rare. Maybe you could get your local shop to run a compression check and test the ‘leak down’ rate to make sure.

  8. David Evans says:

    I have an XJS facelift 6 litre which has had a few improvements done (extractors/ K&N Air filters/ stiffer springs and sway bars) and it is great car to drive. I noted on an article on the Brandenburger Lister Jag that they changed the intake from 2 plate to 4 plate. Could you explain what that means? If it was with Carbs I could understand but this was with the 6 litre engine which I thought came with fuel injection as standard. What is the benefit of a “4 plate intake manifold” and would it be easy to retrofit? Many thanks. Your above explanation has been very informative.

    • Ralph Hosier says:

      The big Listers used four throttle bodies, instead of the normal two, to cope with the extra air flow from the other engine mods. They were available with longer stroke cranks to take them up to 7.5 litres as far as I can remember, and they had wild cams, massive valves, ported heads etc. In race tune they were good for over 600bhp and made a sound like cave giants screaming a battle cry!

  9. Michael E Halbrook says:

    Very much enjoyed your walk through of the systems on this great engine. I’ve owned two XJSs and a series 1.5 E type. I get to work on and around Merlin and Allison V-12 aircraft engines, both of these have gear driven overhead cams. I’ve always assumed the Jaguar V12 used chain driven cams for reasons of economy in the design, I was wondering if you knew if there were other design considerations that favored chain driven cams.

    • Ralph Hosier says:

      Gear driven cams are rarely used on car engines, the only one I am currently aware of is the old Rolls Royce / Bentley 6.75 V8. Cost is an issue but usually packaging the gear train in a tight space proves problematic without using a long train of cogs, which in turn would add weight. Also gears tend to be noisier, Rolls Royce went to great lengths to get theirs quiet, and it is a lot easier to make chains near silent.
      The Merlin is an inspiring engine, sounds like you have a great job there!

  10. Thanks for a great article. You manage to make a complicated subject almost understandable!
    Could you give me any ideas why my 89 XJ-s V12 coolant system pressurises so quickly on start up from cold? Within a couple of minutes the rad hoses are hard to the touch. Obvious diagnosis is leaking head gasket with that high compression. But there is no loss of coolant, the coolant level never drops, and when tested the coolant revealed no trace of exhaust gas. She runs with the needle well below the N of the temp gauge, and when cold there is no gas on top of the coolant in the filler pipe. Any ideas?
    Michael Harcourt

  11. Ade Vickers says:

    Nice article! I’m in the process of stripping a pre-HE XJS down, it’s been parked up for over 16 years so a large amount of the car has – naturally – dissolved… but I’m hoping to rescue her & make her into a racing car (too far gone to go back on the road, I fear). I’m looking forward to tuning that old 5.3 to give me some serious horsepower (500+ is the goal). I will be going with 12 ITBs (from 2 BMW M3s) with their injectors, I hope to retain the original Jag heads, while it looks like porting them to match the BMW throttle size will be impossible, I hope that the constriction will at least speed the air/fuel mix up & promote better “ramming” an swirl/tumble…

    Anyway, the thing I was going to say is, once you’ve got rid of that massive mess of tubes, and those awful inlet plenums, the whole engine suddenly becomes a lot less daunting… and a whole lot more tunable I think…

  12. Randall says:

    Outstanding article, enjoyed the information and will definitely take a lot of it out to the garage. I purchased a 1988 XJS Hess & Eisenhardt, last of the restore is figuring out the routing of the vacuum lines. She is running fantastic, and I was actually able to purchase a simi-new top for her, Now working. Thank you again for the knowledge transfer. RCB

  13. Steve says:

    Good evening Ralph.

    JAG V12 F5000

    I am a avid V12 fanatic of any car, I work on Jags & Ferrari.

    The Jag V12 has may issues before getting to a serious racer, TWR proved this went it went through its development for racing, but, once built correctly its a marvel. One needs to remember the V12 originally was built as a low stressed production unit, in racing its the opposite. Again I note TWRs book for newbies.

    I am constructing a scratch build of the first ever Jaguar F5000 from the base frame/chassis drawings contained in Peter Wilson’s book of the still-born Jag F1 in the 1960s. So far I have done the frame per specs and quite impressed with its inherent strength, I am now re-engineering the Jag V12 for an open wheeler F5000 style (more like a 5 litre BRM). I expect 90% of parts will be Jag and modified, full vent disc all round (XJ40) on S111 spindles/uprights, modified wet/dry sump, Lucas PI mechanical system, modified inlet/exhaust system with 3 x 80mm 4 into1 butterfly trumpet stacks, 11:1 comp ration from modified Jag pistons, Jag suspension/shocks, trans hmmm??? probably Hewland, weight target less than 600kg. Operating rpm range 5000 to 7500. Rims 15 x 8 front, 15 x 10 rear.

    So far I built 2 test frames to arrive at final.

    Periodically pics will be posted on website as development progresses.

    Steve Burrows

    • Ralph Hosier says:

      What a fantastic project! I look forward to seeing it develop on your web site.
      It’s going to be quite a challenge to meet your weight target, the basic engine weighs half of that!

      • Steve says:

        Answer to weight, my calculations for dry weight for a Jag F5000 V12 are: V12 stipped down is around 240-250kg (no aircon, alternator, lighter starter, no TC, no cast iron exhaust, dump the manifolds, air cleaners etc…, Frame about 50kg, gearbox 65kg, ancillaries, fit out, radiators etc say 100kg, unsprung weight 120kg being tyres brakes light rims, total dry weight 565kg. Wet weight with driver add 80kg for driver, 120kg fuel water etc.

        I have redesigned the wet sump to dry using XJ40 oil pump.

        I note you are a motoring writer, why don’t you do an article on this project, as I believe in the near future Formula Libre will emerge as a cost effective way to enter motor sports, particualy for open wheelers.


  14. Steve says:

    Hi again Ralp, you can view some progress by googling “Jagmania Australia” or

  15. Warren Jones says:

    Excellent article Ralph, it’s always good to read a positive perspective on Jaguars almighty V12. So many people bad mouth it, but how many V12 cars can you buy for under $10K. I live in Australia and Jaguar is the only one. I own a 1989 XJS V12 and drove it 7000km across Australia try doing that with a 1980’s Ferrari V12.

  16. Pingback: light reading about the Jaguar v12 - Jaguar Forums - Jaguar Enthusiasts Forum

  17. jurgen says:

    MBE Systems , England have a good ECU that can handle V12 engines !!!!

    • Ralph Hosier says:

      I have used MBE 941 units many times in the past, great people to work with. Not sure they are still selling them though.

      • David Evans says:

        The Motec M800 is also good but a little expensive. I have just purchased some AJ6 Engineering Intake manifolds which will (hopefully) significantly improve the responsiveness. A more lively Cam and a flexible ECU such as the MBE 941 or Motec M800 will make it much more interesting. MBE still exist. Cheers

      • jurgen says:

        one Point: as i have built about 250 V12 engine in my time with Jaguar, i learned it pays off if you take some time to get camtiming absolutely parralell and as well the throttle body’s and dont forget the Valve clearence, this engine reacts very sensitive on Valve shimming ! a friends XJ12 we got to the point of reaching 7000rpm on Germany’s Autobahn !!
        dont forget the Fuel pressure Regulators, as they are adjustable !
        with fine Tuning you can make that Engine running like a dream.
        have a nice weekend.

      • David Evans says:

        Many thanks. My car has been converted from auto to manual (it is a facelift ’94 V12 6.0 litre) using a Getrag 5 speed. I am gradually turning into the car I want it to be. I will post a picture when it is done. Have a great weekend.

  18. Warren Jones says:

    Fuel pressure regulators are not adjustable on the later models, not sure when Jaguar changed but my 89 has fixed regulators.

    MegaSquirt is a great low cost option ECU, and loads of Jaguar V12’s are now powered by MegaSquirt. Admittedly you do need to know what you are doing, they are NOT plug and play.

    • jurgen says:

      if of any interest, on the V12 E-types i used Golf IV Fans and the Golf IV fan switch, they have 3 speed stages, keeps Temperature better under Control, less noisy and save electric Power.

  19. Charles says:

    Hello Ralph

    Great article and you never stop learning when you own a Jag V12. I had an e-type for many years before the XJS HE. It was the first HE to be available in the little Island of Jersey where I live, so it is quite old.

    There are few people here that will do any work on it and it has just developed a cold start problem. There seems to have been so many small mods done to this model over the years that no single manual will really help. It had a mod shortly after I bought it in about 1983, which replaced the fuel rail (as far as I can remember) and left two cold start injector connectors taped up and not used. There were changes to bits of wiring here and there and an odd air filter appeared. It is a long time ago.

    It runs really great but has become difficult to start on cold mornings. Once the engine has run for a minute or so it’s fine. The cold start relay does not appear to work but is not faulty. I am not sure where it receives it supply voltage from but it is apparently only fed while the starter motor is actually turning over.

    None of the manuals say much about this problem and my engine looks different in several ways. It seems that every HE is one of a kind.

    Any help would be very much appreciated!

    Best wishes


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  21. inspace says:

    I think this is a great article and possibly I have missed the answer because I have spent so much time searching I am loosing the will to live. So I will ask! Is it possible to use the edis system on the latest v12 jaguar incarnation on an early e type? i mean it seams the most logical route to go instead of all the aftermarket suck it and see attempts I am reading about. People trying all sorts of stuff to get it to work when Ford already did it or am I seriously missing something. I want to convert my E type V12 to dizzyless efi system but I am really struggling to find someone who can help who doesn’t want 10k plus to do it. Can anyone shed some light here PLEASE

    • Ralph Hosier says:

      Well, it is possible, but not simple. The distributor less system is an integral part of the fuel injection system, so you would need the whole ECU, wiring loom, injectors, manifold, fuel pumps, regulator etc. Crucially it needs the flywheel and engine speed sensor too, and earlier engines didn’t have the locating boss in the block.
      Then there is the issue that fuelling and spark timing are tuned to a lower compression 6.0 engine.
      It’s a lot of work to convert a pre HE 5.3, it would be less work to fit a complete 6.0 engine with the system already on.

      • Inspace says:

        I can appreciate that its a whole lot of work and arguably do the benefits justify it. That said lots of owners, enthusiasts & seemingly jaguar itself admit to the fact that the. 12 E Type was always intended to have injection. There are articles out there in book format talking you through converting using a HE donor & remapped ecu to achieve this. This is also a lot of work but it is been done by companies such as etypeUk and Etypefabs ( now sold to or seemingly sold to Hudson’s sadly). In the book supporting this conversion written by AJ6 Engineering they also cover a late engine swop but suggest. Of using this engine because of the edis system and that does involve some engine machining too. I mean pulling a V12 out of an E Type is not a small job, residing to suit injection isn’t either. To do all this for a system that is on a 25 year old XJS known to have its faults and as you put hugely completely plumbed to overcome advance etc. The reason Aj6 champion the more conventional Efi conversion is to do with efficiency and reliability but I can’t help feeling the XJS system wasn’t heralded as that reliable or again am I reading the wrong articles. I am truly a junior in this field so please don’t think my ignorance is flippancy I just want to know more 😃

      • Ralph Hosier says:

        Yes, having owned and tuned the older xjs injection system I agree that it’s not as reliable and quite complex.
        You could machine your block to accept the late edis system, but again that involves taking the engine out and taking it apart.
        So there are several paths, none simple.
        Arguably it’s easier to fit an aftermarket system and combine efi and ignition. It would need mapping on a rolling road but you wouldn’t need to remove the engine etc.
        Also worth noting that it may devalue your car, E-Type s are valued for originality, sadly.

      • Inspace says:

        It’s a great subject Ralph, one I feel that would open another can of worms. Does improving a cars reliability devalue its originality. I do agree with you absolutely but anyone who dare I say puts aftermarket suspension, improved brakes and so on is moving from originality.
        My feeling are that although I realise the E Type iconic I am sure we’re the technology available the jag engineers would have used it so proven by the natural evolution of the XJS. Changing a cars phisical presence on the road or internally is another issue.
        The very very expensive E type copy now available that is around 600k made by Eagle sells an image but if you explained that it started badly & you had to use a lot of force to stop the thing it may effect there sales.
        I will forge forward in search of that information and let you know the day I find it.
        Thanks for the chat I’ve enjoyed it.

  22. Micah Rutschmann says:

    Amazing article! So much great information in here! I had a quick question for you if you’re still around. I’m currently building an MGB and have shoehorned a 1983 Jag V12 HE into it. The engine came out of a deteriorating XJ12 and I got a set of E Type carburetors with with the deal. We mounted the carbs on the engine and have had it running a couple of times, but is this combination of pre-HE carbs on an HE engine a good idea? Is it going to cause any problems in the future? Any info regarding this would be appreciated!
    Cheers from Canada!

    • Ralph Hosier says:

      The E Type was not as powerful so you may find the carbs a little restrictive at high rpm. They may need re-jetting to avoid it going lean and knocking.

      • David Cox says:

        Ralph, I am looking for a service book for my 1986 V-12… it is housed in a XJSC… and I am in need of the shop manual. Any suggestions?

      • David Evans says:

        Ralph – I have enjoyed reading your various reports and explanations over the years. I have a Facelift 6.0 Litre XJS and have undertaken the following to improve it:
        Manual conversion (Getrag 5 speed), mild race cams (prepared by Mike Roddy racing); AJ6 Engineering Ram Jet Intake system; Tig welded extractors, Autronic Computer system; the usual improvements (sway bars and springs); some AP Racing discs at the front; Jag ventilated ones at the rear; TWR suspension (shockers etc). Yes – it was all a bit expensive but the car is fabulous to drive and looks the part. If you have interest I will send some photos including the dyno results once it is all complete in the next few weeks. The car also has some small finishing touches with hand made wheel caps from aluminium billets engraved with the growler symbol. Regards David Evans – Melbourne – Australia

      • Ralph Hosier says:

        Sounds fabulous! Good luck on the dyno.

      • David Evans says:

        Ralph – the Dyno is showing 300 bhp at the wheels which is good however the car has such a lot of heat in the engine bay – I am losing a lot of power as a result. Clearly a revised cold air intake is necessary – however are there any other methods to reduce the hot air even at idle that you might suggest? Just to reiterate what has been done to the car: AJ6 Engineering Intake Manifolds (Ram jet), Extractors, mild race cams, Autronic Management system and conversion to 5 speed Getrag. Venting in the bonnet would probably assist but I am reluctant to do that just yet. Some sort of insulation maybe around the extractors? Look forward to your thoughts. The temp seems to be at 100 – 110 C most of the time. I could change the coolant to a totally different style I expect but I am not sure if that will make a big difference.

        David Evans – Melbourne Australia

      • Ralph Hosier says:

        When I raced the usual technique was to Jack the rear edge of the bonnet up so there was about half an inch gap to let the heat out. That was easy as we all used bonnet pins and not the standard bonnet release. Alternatively put louvers in the bonnet. Either way the problem with the xjs is getting hot air out of the engine bay, not getting cold air in. Exhaust wrap may help, but it’s fiddly and can fall apart.

      • David Evans says:

        Thanks Ralph.
        The Lister 7 Litre used bonnet vents from memory.

        I have often thought of adding a pair of super chargers or turbo chargers however there seems to be no room for them (and their coolers). Not sure how the Lister cars managed it.

  23. Bunnet says:

    I was unaware that Jaguar had used Marelli, for electrical.
    I know it been in Ferrari, Maserati and Fiat for years because that what I usually work on. But I be honest I’m not expert like you in this tuning business, as matter fact I venture to say I need full class

  24. Damian says:

    Hello, great forum.. Seemingly I have an intermittent brake issue on an 86 V12.. Brakes getting hot and pedal gives me nothing, cool down and then work.. Like the fluid is boiling up and the front calipers are binding as I am getting lots of brake dust on the front, new calipers and pads renewed on front and back recently. I had to use the handbrake to slow the car down recently when I had sudden loss.. Sent back to mechanic to Investigate, bled the system thinking maybe air build up, brakes failed again, used the handbrake again and expected that I had damaged the pads worst case the seals, mechanic seems to think the brake issue is due to the fact that I have been driving around with handbrake on which is just preposterous.. I have owned a few XJS’ and I am very familiar with the handbrake system and certainly know if my handbrake is on or not! Could this be a lazy master cylinder?

  25. DJR says:

    I wondered if any could point me toward info on manual gearbox conversion for the V12 HE? I want to build my ratty XJS into a low-cost endurance racer and enter it in the ChumpCar or Lemons series here in the States. I’ve seen a couple of XJS campaigned in these series but their performance and driving satisfaction has been ruined by the 3spd Auto slushbox.

    There are a number of outrageously expensive kits for a manual conversion out there. Alas, I am not blessed with generous finances but I am more than willing to rob good used parts from BMWs, Mustangs or Camaros from scrapyards and fabricate adapters and so on.

    Somebody somewhere must have done this on the cheap at some point…I’d be interested to learn what they did and how they did it if they do indeed exist.


    • Ralph Hosier says:

      The bigger Getrag boxes work well, they were on BMWs, later Jags etc. Or the old Borg Warner T5 or T6 is a nice option too, think it was on Mustangs. Either way it will need a modified bell housing or adapter plate. The new owner of mine has fitted the Getrag, google Rust 2 Rome Black Pearl and his build blog should come up.
      Sorry for late reply.

      • DJR says:

        Thanks Ralph. There were apparently only 24 Getrag 5spd XJSs shipped to the US, all 6cyl cars. These were sent over by BL in the mid 80s for the use of Jaguar employees/sales people and were not sold to the public as brand new vehicles. I only know this story as one of these cars recently turned up on Craiglist in New Jersey. The man selling it was the son of one of these such Jaguar salesmen, now retired.
        Seems the easiest thing to do to convert to a manual gearbox is to find a good 6 cylinder XJS donor and simply swap everything over that’s needed. these donors must be getting thin on the ground even back in England.
        It would be an easy and pretty cheap thing to do if not for that infernal Jaguar-specific transmission bolt pattern on the engine blocks.
        The Black Pearl is a great car and I love the videos, the owner seems a really good guy too organising the Rust 2 Rome rallies.

  26. David Green says:

    I used to work at West Yorkshire Foundries in Leeds,UK,part of British Leyland,where the cylinder blocks and heads were made,I started there in 1970,working on the various plant that they had,and I was walking down the yard one day,and saw a V12 block,with WYF,and Jaguar on the casting.I thought,Jaguar do not make a V!2,but,about 3 years later,Jaguar announced the V12.British Leyland had a publication called The Leyland Mirror,and had an article stating that the new V12 developed 500 bhp,and they also had a cut out version on display.The engine was too powerfull,and was de-rated to 360bhp,and this was still deemed too powerful.They de-rated it again to about 260 bhp.A few years later in the Mirror there was an article abut 2 Americans who used an XJ12 for racing,that had been “specially tuned”to get 500bhp,ha ha,they had just put it back to the original spec,and,I think it used carburettors,and not fuel injection,as it was still early days for that then. David Green,Leeds,UK

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  28. has anyone used the 12cyl fi engine for an aircraft build

    • Ralph Hosier says:

      Yes, a scale Spitfire. Using a alloy girdle plate to ofset the crank down for more stroke, with Siamese liners they got a displacement of 10.5 litres.

    • David Green says:

      In 1970 I started work at West Yorkshire Foundries in Leeds,UK,which was part of British Leyland ,making castings.I noticed a V12 cylinder block one day,and I thought,they do not make a V12,about 2 years later,they introduced it to the public.The block,cyl heads and I think,the sump were all made aT WYF.B/L had a magazine called the Leyland Mirror,and,one article was about the V12,stating it gave out 500bhp in standard trim,of course it was de-rated for road use.A couple of years later,another article about 2 Americans that were racing an XJ12,and it said it had been specially tuned to get 500 bhp,rubbish,they just put it back to original spec.They also had a cut away version there for a while

  29. rui says:

    Well done thank you for sharing it sure lays a good attitude and eliminates the mith of a nightmare

  30. Pingback: The Jaguar V-12 engine – Finish Finale UK

  31. Pingback: The Jaguar V-12 engine

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