XJ6 or XJ12 for performance-minded first time owner?

(Tony Higgins) #1

Greetings Jag lovers,

As I approach retirement I’m seeking a project car -which from what I’ve read in the forums so far, describes any Jaguar up to and including the Series III XJ6! Therefore, I have tentatively decided on that car as a target for my search. My novice-to-Jags self has come under the impression that they are not horrific rust buckets, and underappreciated due to a perception that they are unreliable -and therefore relatively cheap. I am wary of this impression because it has mostly come from on-line research. One of the reasons I joined the group is to get honest information from mechanics and owners. So feel free to correct my impressions! I have always thought the cars themselves are beautiful, so to have a clean, good running one would be a joy (or so it seems!)

After driving small, reliable commuter cars for the past 30 years (and I’m keeping the current one) I’m ready to turn the corner and have the full-on, engine apart, seized nuts, grease-stained manual experience! Speaking of manuals, one of the first projects I would like to tackle is to swap in a 5-speed transmission. (Why should the ROW have all the fun?) Another project I would equally enjoy is increasing the horsepower. With 4.2 liters it seems SOMETHING can be done to surprise a 5-series or Mercedes driver.

On that last topic, if the six is an impractical place to start, (because of scarcity of performance parts, for example) there’s the XJ12. It probably has the HP I’m looking for out right of the box but one look under the hood is not inspiring. Are there any opinions in the group as to which choice -XJ6 or XJ12 – can bring better satisfaction? Is one or the other a better candidate for a 5-speed conversion?

(tony) #2

I converted a S2 V12 to 5 speed manual (Supra W57)

The V12 has significant HP advantage over the 6

depends on budget

either can be converted, have a good look on the archives

An already completed conversion is one thought

The XJ6 also came with factory MOD version

see other engine/trans conversions in “lumps” category

Lots to think about !

(Robert Wilkinson) #3

Welcome, Tony. From folks I know who own both, the XJ12 is the way to go.

BTW, I suspect that in a dream tonight I will envision you and fellow XJ lister RustfreeMike having a beer together whilst making fun of my car. :slight_smile:

(Pete55Tbird) #4

Sorry to rain on your parade. All unit body cars in the wrong environment are subject to rust issues.
If the cars are not treated to prevent rust during manufacture rust issues are much worse.
Jaguar was able to sell at lower price point by saving on thing like corrosion prevention and depending on
who owned and ran Jaguar at the time of manufacture sometimes shoddy manufacturing practices occurred.
If you can find a RUST FREE car ( think California ) you will be miles ahead.
This list promotes Jaguars but if you read between the lines the warning are LOUD and CLEAR. Pete

(Rob Reilly) #5

Here are some idle thoughts from an idle fellow.
I ran my 74 XJ12 S2 (carbs and manual choke) for about 8 years as my daily driver. It is a wonderful car to drive, which is why it is still here in quiet retirement waiting its turn in the restoration bay. I would say it is too heavy a car for a stick shift, especially in suburban traffic. I prefer the automatic. In good tune the engine is incredibly smooth. Be aware that I got about 12 miles per US gallon when it was in good tune. Smog testing gave me headaches in the 80s but no longer applies to it here so I can now remove the air pump. It towed a trailer easily. It was usually great in snow, but difficult creeping slowly on ice just barely touching the brake, the front wheels locking up while the back wheels wanted to keep driving forward. And one January when the temperature was -28F (-33C) it started and got me to work and back. The only thing I might change is the 74 only USA only rubber bumpers which I think are unfortunate, so I might look for some ROW chrome bumpers.

(Frank Andersen) #6

What are you actually going to use the car for, Tony…?

With great care, attention and expense; you can get some 300+ hp from an xk engine - without compromising engine and driving too much. I would not try to develop the V12 along the same lines. It is not that it is frail, but it is a much newer construction, having already benefitted from general engine development - and some ‘performance’ elements is already included…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

(Carl Hutchins, Jr. ) #7

Dare I ???

My car is now quite pleasing as to “suds”…

The DOHC gas always fascinated me. but, trimmed in far more conventional manner.


(Tony Higgins) #8

Frank, I want to satisfy my yen to get waist deep (mechanically) in a car and drive it occasionally for pleasure. I’ll keep my DD for utility driving. My first car was a Morris Minor that I got free with a spun rod bearing at 17. I pulled the engine, took the block and crankshaft to a machine shop, Got new pistons and bearings, had a valve job done and reassembled it. It was challenging but I really enjoyed the hands on learning. It felt empowering. After that, I worked at some dealers and garages, got ASE certified and then quit after a few years to go to college and get a “real” job. I had to abandon the Morris when there was so much else left to do for it. I really needed a place to work on it but couldn’t manage it. So, now I will have the time and space to get into something nicer and faster (just about anything’s faster than a 948cc Minor!) Not trying to build a hot rod, just do more than make a car run -I want to make it run the way I want it to. I think 300hp would be plenty if I could coax that out by standard methods like raising compression, porting the intakes, cam upgrade, etc. Reliability is important, I don’t want to build something fragile that needs constant attention! Seems like a V-12 would be just the ticket for instant power and I might go that route. However it seems a bit less accessible and probably not as malleable for change. In the end, I think the right car will find me.

(Tony Higgins) #9

Hi Rob, thanks for your thoughts. I did drive a XJ once -early 1980’s -when I worked at an independent shop. I don’t remember if it was a 6 or 12 but I do remember it was silky smooth and I loved the cabin. It seemed very luxurious and I was impressed that it also handled well.
I have heard that the HE V12s with their L-jettronic FI can achieve mileage in the low 20’s on the highway. If I do get a V12 that’s what I would aim for. I really need to drive some of these cars to feel how they accelerate and handle. I would definitely go for ROW bumpers if you can find them, 1974 was a curse to all cars sold in America!

(Tony Higgins) #10

Tony, I think I’m hellbent on having a manual because I have always driven them except for my current DD and I wish it was a manual! Why did I buy an automatic? It’s a long story I won’t bore you with. So, If I want a Jag with a manual, I have to find an early one like a MK2 and those are scarce. I don’t want anything newer than 1992 which I believe is the first year for OBD and I want to be free of that. I think a manual XJ would be really interesting. Might even make it attractive if I ever try to sell it. 6 or 12? I think I’ll have to plan for both and jump at which ever one appears on the horizon first.

(tony) #11

Several Sedans had manuals, including XJ6, and all preceeding sedans

XJ12 never came with a factory manual

XJS came with a manual, but they are very rare

4 speed, or the preferred manual + overdrive

imo, an XJ6 is not a performance car, even a manual will not make it so, as it is too heavy, and the engine lacks power.

An XJ12 with a 5speed is nice, but still a heavy car, and will not outrun a modern V8 from the lights

The fastest XJ ever been in had a well setup 350 Chev in it

(Michael Rogers) #12

I’ve had older jags for decades, thrashed them and never had a problem–they’re made to race, the early C jag engines were essentially the same as that in the jags for decades, The tranny is STRONG but only if meticulously assembled is a smooth shifter, typical move is to swop in a 5 speed or the later all syncro + OD tranny. The small saloons: Mk-1 especially weigh less and a bigger engine will screw right in There aren’t any weak points unless you’re really thrashing the cars then few! The 12 is a totally different project which with enough money will blow lots of stuff away research the factory race cars.

(Frank Andersen) #13

It’s the right line of thought, Tony - I would also suggest carbs, which are more tuneable than the standard EFI. To utilise high compression you need high octane and an upgraded ignition system - the present ignition system is too primitive…

But the secret of horsepower is rpms; the more air the engine can digest the more fuel it can burn - and petrol is what gives the power. But rpms requires very careful balancing of the engine, among other things - and one way of increasing air ingress is more cubic inches. But 6 carbs will help with both breathing and fuel distribution - and heaps of gears will keep the revs up…:slight_smile:

The xk is no sow’s ear, but making it a silk purse still requires several stitches. A V12 has the instant power, but less potential for improving it…

xj6 85 Sov Europe (UK?NZ)

(Mark Lee (Pay Pal Patron)) #14

I love the V12 and it’s silky smooth power delivery. However, I really don’t care much for working on it. Space is tight to say the least, and so much has to be removed or displaced to perform simple tasks like changing plugs.

Then there’s the XK6, I adore this engine. It’s a beautiful piece of hardware. The performance of a properly tuned XK6 is impressive. Depending on how deep your pockets are, it’s very doable to squeeze 300bhp out of a XK6 with the simple mods. Porting and polishing the head, freeing up back pressure, and 9.5 or 10.5 to 1 pistons. Best of all it’s easy to work on.

At one time I was searching high and low for an XJ12 because I was certain I wanted one. Now that I’ve been tinkering with my XJ’s; I’m not so certain that I do.

My two cents.

(Doug Dwyer) #15

I drove a Series III XJ6 4.2 for many years. Then a V12 XJS. I now drive a V12 Series III.

The V12 in USA trim delivers about 90 more horsepower than the 4.2 so, very obviously, it offers a lot more performance. Right off the bat, you’re ahead of the game, performance-wise, versus a 4.2 car…just as you say. A bit rare to find a Series III V12 in the USA…but they’re out there.

IMO, extracting significant power increases from either engine is not an inexpensive thing. Unlike many more common engines/platforms there really isn’t much out there in terms of high-performance equipment.

Performance increases are made more difficult, too, by the Series III cars’ weight. A Series III 4.2 has a curb weight of about 4100 pounds; the V12 about 4300 pounds…well out of the lightweight category. Further, most were built with 2.88 final drives which, in combination with the weight, tends to blunt the net result of any horsepower increases.

Personally i’d suggest seeking out a V12 car…but at the same time will admit that a V12 isn’t for everyone. Many of the V12 horror stories are overblown (and offered up by those who have never actually owned one!) but they do have more quirks and do typically require more owner dedication and enthusiasm, particularly during the ‘sorting out’ process… which the owner of any old Jag must inevitably slog through. But, greater effort yields greater rewards.

The ease-of-repair aspect with a V12…or, rather, lack of it…is very easily addressed. You must work slowly and deliberately, and simply resign yourself to the fact that you’ll often have to remove 2-3-4 or more ‘things’ to reach the widget your aiming for. Don’t fight it. Embrace it. Learn to savor every turn of the wrench. Remaining philosophic is everything :slight_smile:


(Robert Wilkinson) #16

Amazon.Com: Zen and the Art of Jaguar XJ12 Maintenance, Dwyer, Doug, 2018, Hardcover. Also recommended for Audi owners. :slight_smile:

(Tony Higgins) #17

In the past three weeks, I have been searching for cars and reading everything I can find related to Series III cars and rust. I also ordered Dave Pollard’s Series 123 Buying Spec/Restoration book from Books 4 Cars. I have learned a lot of good information from the archives, so joining this group has already paid off! A key thing I have learned is that these cars will rust anywhere. Even California cars can have rust at the lower corners of the front and rear windscreens. I read this then saw it in pictures of a car in Nevada that was claimed to have lived all its life in LA. I also found Doug Ingram’s pictures of his XJ6 before and after windscreen removal which showed massive rust under the weather strip that looked deceptively minor before he removed it! So, now I am wary of pictures of prospective cars showing no rust in these areas. Better to accept that it may be present to some degree in any car I choose and plan accordingly.
To that point, I am considering a 1984 V12 VDP-HE in Pittsburgh; a Canadian car with 45k miles. At 300 miles away, it’s the closest prospect. The dealer to his credit has posted many pictures. They indicate to me a car that has spent most of its life outside but not necessarily driven on salty roads. Here’s why I think so: There is rust under the lower left rear of the rear windscreen and paint is starting to bubble in the lower part of the fender behind the rear door on that same side. I remember reading that rain/snow-melt can leak in around the rear window, run down the inside of the fender and collect there. Also, in close-up pictures, you can see the paint is “crazed” -the color coat has fine cracks. But this is only seen on the horizontal surfaces, the sides look fine. So, with this damage happening over 35 years in a rust-belt city, you’d expect the undercarriage to look awful. Not so, because other pictures do not show much evidence of salt exposure. The undercarriage shows a nominal amount of surface rust; the engine bay has no rusty parts and the inside bottom door edges are clean. Inside, he driver’s floor carpets look a bit worn but pretty clean with no salt stains.
This car might be in this state no matter where it lived. Please take a look and post your opinions. The dealer is International Motors of Pittsburgh. It’s the only Jag they have. (I tried cutting and pasting their URL but it wouldn’t work for some reason)

(ronbros) #18

if you are looking for XJS ,V12 Hi-performance engine ,4 speed auto, HD rear LSD.etc.



(Frank Andersen) #19

That’s an XJS, of course, Ron - but no worse for that…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

(Aristides Balanos) #20


My two cents:
You are correct with your assumptions.
Car looks quite good from the photos, interior and exterior, and the engine is clean and looks original.
Besides oil leeks and overheating issues you should check, the yellow cooling fan will need to be changed with the updated black fan before it explodes.

ItHasNoRust ?
It’s a Quebec car (therefore the French stickers on the fuel caps), and has indeed seen salt in his life, the rusty suspension parts testify that.
As you say, hopefully it’s just surface rust…

The rear wind screen has to be removed and the rust repaired, common problem with water leaking inside the channels.
Same with the front screen if you want total piece of mind.
The rust on the wheel arch looks minor.
The paint is crazed, same as mine, therefore repaint necessitates sanding it to bear metal.
Sunroof needs adjusting.
Chrome is good and panels look straight.

Interior is decent and repairable
VDP seats, door covers and dashboard is a big plus.
What surprised me is that the lower center console is not wood.
The varnish is peeling and this is quite a big job but you can do it, or part of it, yourself.

If it drives straight, brakes are good, no major leaks and noises, A/C and everything electric works it seems to me that it’s a very decent car.