[Editor's Note: We originally ran this article a few years ago. Some information may be different.]
Out of the thousands upon thousands of Readers’ Rides on our webpage, a Jaguar XJS is the sixth-highest-rated car. Okay, so it’s a full-race example prepared and campa…
I've bought Jaguar XJ-S's for as little as $300. In fact I was once given a very early (1975) XJ-S because the junk yard had almost no call for parts. That complex looking V12 intimidates most but it's amazingly strong and durable. Minor little things tend to let it down. The distributor for example gets it's lubrication when the cap and rotor are removed, a screw removed and a few drops of oil are dropped in every other oil change.. Except almost no-one is aware of that requirement. As a result a lot of mechanics get their first look inside a V12 in a vane attempt to restore the performance or prevent overheating.. I hate to tell you how many really good engines I've picked up for as little as $50 (normal junkyard price tends to be between $500-$1500) for simple issues like a seized up distributor.
Yes the rubber hoses in the vacuum/fuel systems tend to harden and crack. However they are easy enough for a D.I.Y to replace. Doing so every 5 years or so prevents a lot of issues like rough running or fires.
On the other hand everything on a Jaguar is extremely stout.. The rear ends constantly find their way into hotrods and Cobra replicas making over 500 horsepower.. The GM turbo 400 transmission has the heavy duty parts found in Ambulances and tow trucks.. and the whole engine looks like one of those 8000 horsepower top fuel engines. The Mains are over 3 inches and the rod journals are 2.3 inches (compared to a small block chevy's 2.00 or later 2.10) The iron sleeves just press out if anyone could ever actually wear one out..
From 1975-to about 1978-79 the transmission was a cast Iron Borg Warner (yep! a version of the Studebaker transmission from the 1950's) the less said about it the better! But the early (up to 1980) fuel injection is the easiest to fool and has the biggest injectors.. However it's analog not digital, not a single microchip. Only the last years with Ford had any IC networks.
In 1981 they introduced the H.E. It was designed to improve fuel mileage and meet California's smog regulations. They achieved that with a combustion chamber similar to GM's fireball six of the 40's and 50's . The sad thing is the performance potential of the early (1971-1980) flathead was lost.. Those heads flowed like an inverted Hemi with the combustion chamber in the piston. In fact all race cars used that early flathead because of vastly superior flow potential.. However the H.E. went from a compression ratio of 7.8-1 to 11.5-1 while still using pump (92 octane) grade fuel. The good news was because of a more efficient transmission, taller final drive ratio, and higher compression fuel mileage went from 8-10 to 12-17 MPG.. Not bad for a 4200 pound car..
Be aware that at best the XJ-S is a low production car.. Early on annual production seldom reached 3000 and one year was under 1000. In fact total production of all V12 engines (including XJ-12) didn't begin to achieve break-even. That changed with the advent of the H.E. engine and it's better fuel mileage and transmission..
With the introduction of the 4 valve all aluminum six cylinder reliability took a dramatic upswing. In fact GM was considering buying Jaguar and in doing their due diligence discovered what a great engine the 4 valve all aluminum engine was. They then bought it (and tooling etc.) modified it to use in their new Mid range SUV's Trailblazer, Envoy, etc.
Once Ford bought Jaguar quality went up dramatically and so did sales.. From 1992 until end of production in 1996 the engine was stroked to 6.0 litres from it's original 5.3 increasing power 23 horsepower while still increasing slightly fuel mileage (Better fuel injection and crank fired ignition)
My dad had one for a few years the only car I knew that the fire extinguisher got good use in. Apparently if my memory is correct they can leak oil into the catalytic converter.
Beatiful car yes, near an e type in beauty no in my opinion. Expensive if you don't do your own work.
tripp wrote: My dad had one for a few years the only car I knew that the fire extinguisher got good use in. Apparently if my memory is correct they can leak oil into the catalytic converter. Beatiful car yes, near an e type in beauty no in my opinion. Expensive if you don't do your own work.
Fire extinguisher? Well it probably wasn't oil leaking rather one whole bank of the engine shut down and pumped raw gas into the converter due to the distributor issues I mentioned..
As for expense of working on? Due to the complex appearance of the engine it's extremely easy for a less than honest (or perhaps ignorant) mechanic to run up a sizeable tab. I've seen water pumps, headgaskets, radiators, fans rebuilt/replaced etc. all in a vane attempt to fix the frozen distributor issue..
A few drops of oil in the proper place every other oil change would have solved that!!
Highly plausible on it being raw fuel I just know there was not than 1 engine fire before it eventually had an issue that was too expensive to fix from my dad's perspective. Trying to remember back 10+ years ago for the details.
frenchyd, thanks for the additional input. (And once you say that a transmission is ambulance-tough, you kind of have me; I have the same TH400 in my Pontiac wagon, in fact.)
My buddy has an rs, it's kinda cool.
Just be aware that a rusty Jaguar is a money pit second to none.
A friend' father owns an XJS he bought new - a very rare fawn sort of gold colour. It has less than 5,000 miles on it as it was used for sunny weekends only. It has been sitting under a carport for many years. It is rusted to ratE36 M3 just sitting there, having never seen winter or even wet driving conditions, nor salt on the road.
In reply to wspohn:
Just sitting is tough on any car. Surface rust isn't a real issue except it will require a repaint to make look decent again but you are lucky in that Old Jaguars have a lacquered based paint which is easy to spot in by a skilled painter. Matching a rare paint isn't as hard as it once was with the new digital matching equipment. However good luck finding a skilled painter, with access to the new equipment and someplace to blend up a small amount of paint..
As far as a money pit, a combination of a lack of knowledge and imagined complexity has caused many a trusting owner to allow an unscrupulous mechanic to "rebuild" a V12 simply in an attempt to get it to run properly or not overheat. A properly trained mechanic would check to see if the distributor is frozen due to lack of lubrication before going off on expensive rebuilding or modifications of the cooling system.
However if there are holes in the body etc.. don't waste time and a lot of money trying to rebuild rust. Go buy a car without those issues.. if the mechanical bits are that good do a swap into the good body.
David S. Wallens wrote: frenchyd, thanks for the additional input. (And once you say that a transmission is ambulance-tough, you kind of have me; I have the same TH400 in my Pontiac wagon, in fact.)
That V12 has a shocking amount of torque for such a small little engine.. hence the heavy duty big block internals. I have taken apart a transmission where the internals were swapped out at the transmission shop in a vane attempt to fix the hesitation caused by the common TH400 dropped seal issue. (caused by someone changing the fluid and not knowing what they are doing).. It's happened to lots of GM cars too!
That's the first I've heard a Jag V12 referred to as a "small little engine"...Yeah, all 700lbs of it. 
A guy I know has a hobby of building V12 motors. Any V12. He says the stock Jag V12 bottom end was good for 1,000 HP.
Driven5 wrote: That's the first I've heard a Jag V12 referred to as a "small little engine"...Yeah, all 700lbs of it.
It starts out at 326 cu.in. so yes it's small. It's also very narrow, 22 inches,24 with exhaust manifolds. Most in-line sixes are as wide or wider. Only 24 inches high to the top of the manifold. It is also at least 32 inches long
As to weight, while the block and heads are aluminum. The crankshaft alone is 100 pounds made of a high quality forged steel. Boring the thick iron sleeves out, offset grinding the crank and using aftermarket connecting rods, using modern small alternators, gear reduction starters, replacing the cast iron pulleys with modern multirib pulleys, it can approach 550 pounds.. Considering that is within 40 pounds of what a Small block Chevy weighs, it's not bad for an engine that can easily go over 500cu.in.
I did it,I feel great about it and FULLY intend on it Being a Daily Driver, a Jet Black 1989 (2/89) convertable.Fuel pump went out and it was parked 10 years ago. I looked for an Hour and cannot find any rust, the interior is trashed from Sitting in the Sun and every thing else that needs replacing from Time and just sitting. I am so Stoked!!! also Has the Lace pattern wheels and very dry rotted Tyres (I will have to learn the Queens English)
Need pics of said purchase! I am looking myself for an XJS convertible... Different than the miatas or bmws I'm familiar with.
Y'all need to come to our Brits in the Ozarks car show in September in NW Arkansas.
Dr. Hess wrote: A guy I know has a hobby of building V12 motors. Any V12. He says the stock Jag V12 bottom end was good for 1,000 HP.
I would say that he's being conservative, 4 bolt mains of over 3 inches, Forged steel crankshaft, Rod journals of 2.3 inches , a block that looks similar to those 8000 horsepower top fuel engines except for 12 cylinders instead of 8, The heads are held on by high quality studs 52 per engine 26 per head. Plus the oil pump is massive compared to a typical engine.. The connecting rods look as if designed to rev over 8000 rpm and in fact were tested to 8300 RPM without issue..
The later V12 from 1992 until the end of production (1996) has a much better crankshaft seals and even bigger oil pump. However only the first 2 years had the Forged steel crankshaft. The last years were made of sintered Iron.
Frenchy, Thanks for looking in, this one isn't without some issues but NO FEAR it is what it is and it's A Beauty. My Vette Is the Hot Rod and I promised my Wife that I wouldn't Start Modifying it before It's Running.
I am a little supprised the rims are only 6 " wide and well it needs Tyres so I will look for some a tiny bit Wider. 90% of the inside will need replacing, all good behind the seats. his son backed the Boat trailer into the D.S. Tail Light but other than a deep scratch on the driver door it's great! Must keep saying NO Mods.
GTXVette wrote: Frenchy, Thanks for looking in, this one isn't without some issues but NO FEAR it is what it is and it's A Beauty. My Vette Is the Hot Rod and I promised my Wife that I wouldn't Start Modifying it before It's Running. I am a little supprised the rims are only 6 " wide and well it needs Tyres so I will look for some a tiny bit Wider. 90% of the inside will need replacing, all good behind the seats. his son backed the Boat trailer into the D.S. Tail Light but other than a deep scratch on the driver door it's great! Must keep saying NO Mods.
I agree with the No-Mods idea.. The XJ-S I picked up had been sitting for 10 years while the previous owner had tried to sort out the differences between the later fuel injection and the original. Had he asked I would have told him there was no power or mileage difference. Marginal reliability improvement maybe and yes cosmetic.(assuming you feel the 6.0 litre looks nicer than the earlier 5.3 in that regard)
Interior parts in a lot of cases are no longer available. Your best option may be another car!!!Find a project or a collision car someone has given up on but the interior bits are still in good shape.. You can budget about $3-500. You may be able to recover all of that by selling off pieces and parts not used. Don't worry that the leather may feel like cardboard there are products out there (my favorite is called leatherique (sp)) that solve that issue and I hate to say this for fear of starting a war but all leather is painted!!! Natural leather is too spotchy to be used raw so it get's painted.. I re-sprayed my MGTD interior back in 1973 and it still looks good today. If the leather isn't badly worn/torn try sanding it down with 400 or 600 grit sandpaper to remove the ridges etc.. I've seen super glue used successfully to rejoin small tears (but it's strictly a one shot approach do not use to excess!!!) If the seam has given up bring it into an upholstery shop to be re-sewn.
Wider tires only increase the turn radius TO UNACCEPTABLE numbers. Unless you are willing to go to fender flares (and then it's resale value will take a really intense trip south).. Accept it as a cruiser without any racing pretensions..
It's weight is the main issue you need to overcome, 4200 pounds. While I've taken one down to 2700 pounds it was completely stripped to race car status.. Yes it would be possible to get it down to around 2300 pounds with Carbon Fibre replacing steel.
French is there a "cheap" way to convert these engines to carburation? It sounds like the fuel injection is not terrible but I like the look of carbs.
My guess is webbers are the only ones and they aren't cheap.
As I Am Making Payments to get this car, no Hurry's, but will take me 'till the end of the summer to pay out . so looking for parts and or repairs I can Plan ahead and be ready for them. I'm excited and will go by tommorow to get some Pics. this takes me out of the Challenge for Financial reasons but not to worry as someone has offered me a seat in their car, Old Dog's stick togeather, aka "Pack Mentality"
Pattyo wrote: French is there a "cheap" way to convert these engines to carburation? It sounds like the fuel injection is not terrible but I like the look of carbs.
Carbs vs Fuel rejection, The early V12's all had carbs. from 1971-1974 California carbs were 242 horsepower while European carbs were something like 271 horsepower. Then they switched to fuel rejection, it kicked it up to 292 horsepower so roughly carbs cost about 50 horsepower over fuel rejection.. (OK I know it's supposed to be injection
) But wait that's not all folks!!! the problem with carbs is the stupid dog leg in the manifold to get the carb to fit under the bonnet of an XK-E. When that is cut off there is a 50 horsepower gain.. (Done by the guy with the MGB GT V12 )
Here's the issue with fuel injection.. Most Jaguars don't have any real way to adjust them. Oh there is a slight adjustment built in for slightly richening or leaning out the mixture but nowhere near modern systems.. There isn't an IC network to be found.. Believe it or not, it's analog not digital!!
An outfit in England (AJ6 Engineering) can adjust things for you depending on what you do to the engine but it's very much a case of you shipping your "computer" to them, telling them what you need and they "adjusting" it to what they hope solves your requirements and shipping it back..
There are ways to trick the system. When I turbo'd a V12 I used a simple FMU (fuel modification unit) that took the boost pressure and as the signal increased it sent a lean mixture signal to the computer so it fattened up the mixture.. It was only $85 back then. Dealing with the timing I took a H.E. distributor and switched it for the Carb distributor basically trading advance for retard. It very much was a kludge system done just to give me a shot at Lemons racing until talking with some official's I found out that basically they wouldn't allow it.
The real power gains that cost next to nothing are to switch to E85 gas. On the V12 there is 100 horsepower waiting for you without having to open the engine up!!** But you need to really fatten up the mixture.. (by about 65%) If you use the earliest injectors in the latest engine you can't get there! So you are forced to resort to something like a Megasquirt computer and while it might exist for a V12 I'm sure no one has mapped the requirements of E85 in a V12 Jaguar..
My solution is to cut the end off the fuel injection manifold and with the aide of a piece of aluminum angle weld on a plate to take 3 (three) Stromberg carbs per side.. (six total) There are a lot of 1&3/4 inch Stromberg carbs around basically the go-to carb of the early pollution control solution.. Jaguar, (6&12) Volvo, Triumph, MGC, etc. etc..
Six carbs instead of 4 gives you 50% more flow and it's merely a needle and jet away from the required enrichment.. Burlen (sp?) carbs is still in business..
Now here's where things get really good! The early flathead engines had only a 7.8-1 compression ratio. while the later engines called the H.E. had not only the needed fuel injection manifold but also 11.5-1 compression ratio.. perfect to take advantage of one of the real benefits of all that alcohol!!!
The flaw will be the distributor! Grab a distributor off the early one and the advance curve in it will work a lot better than the retard curve in the H.E. If you can find one from a European car for the best curve.. (pretty much hens teeth since most early V12's came here to American)
** while fuel mileage in a H.E. will go down to about 7-9 (compared to maybe 14-17) the lower cost of E85 will get you a similar cost per mile..
sergio wrote: My guess is webbers are the only ones and they aren't cheap.
No they aren't cheap, but a set of Webers is only the start.. you can easily spend that cost again trying to get the right set of jet's so the carbs work properly.. That and dyno time.. No they aren't simply bolt on and mess with the screws a bit. Too lean and they will backfire maybe causing leaking fuel to ignite.. Yep there will be leaking fuel.. Too often fuel bowls won't be properly tightened or fuel lines will work loose with all the switching jets etc.. Or the fuel lines will crack from old age/ the wrong line selected/etc. Only a complete compulsive can eventually get a set of Webers running properly..
And here is the main issue with Webers.. The hood!(bonnet to the British) the little stub manifolds required to clear the hood offer no possibility of proper intake runner length. (unless you give up on the less expensive IDF's and use the DOE's with long horizontal runners).. So you spend thousands of dollars and can't make significantly more horsepower because of the short stub manifolds! Not to mention the fact that you may be working with only 3/4 of an inch for air-cleaner!!!
You'll need to log in to post.
