I would humbly suggest reading the recommended procedure for changing the starter on v-12 jag. I worked on 1 once, with a NASA electrician no less. I saw more WTF factory "engineering" than on any other project. It basically looks like they did 1 design pass, made it fit and said "well that's good enough". My absolute favorite "feature" was the AC being used to cool the fuel lines. Never in my life has fixing the air conditioning been a viable solution to preventing vapor lock. Now I am positive there were other ways to do it, but florida heat, a v-12 and a factory design that ran the fuel through the AC made it the "easiest" choice.
We did stick through with it, got it running and the engine was an amazingly quiet and smooth monster. Would I ever work on one again, NFW!
FYI this one was a part of the fire sale depreciation option jaguar included as a standard feature with their fuel injected models. LOTS of tiny rubber fuel lines pointing at hot sparky things. The electronics were never an issue for the NASA dude, but the mechanicals, FML.
BMW uses the fuel cooled by AC lines on the 750il. I wonder if it's a v12 thing - too much heat for regular stuff to deal with?
To Adrian's question: I think it's just a "familiarity" thing. And like people have said, the v8 offers lower weight, more power, and better fuel economy. I think it doesn't solve anywhere near the number of issues that people think it does (ie, power windows? climate control? Failing switches? inboard rear brakes?) but it's a theoretical win/win even if in reality it often ends up not quite as "bulletproof" as people picture.
Adrian_Thompson wrote:
Klayfish wrote:
Well, if a 350 powered Jag bugs you,
Aaggh, I never said they bugged me, I just didn't understand the need.
Very cool car BTW
So, am I to understand that you are bothered by V8 Jags then?
At the time that the swap kits were developed, you could probably find a very good Chevy engine transmission combo for less that $200. Once the kits got out there, it became a thing to do.
dculberson wrote:
BMW uses the fuel cooled by AC lines on the 750il. I wonder if it's a v12 thing - too much heat for regular stuff to deal with?
Some e28 5 series cars had this feature as well, it was more common in BMWs sold in warm climates.
One of the guys I shared a building with could pick up anon running Jag for almost nothing and a 350/350 for about the same. He'd put them together and let the wife drive it around a bit then sell it. It was a bit less than a weekend of labor and he would do two or three a year.
Giant Purple Snorklewacker wrote:
Adrian_Thompson wrote:
Klayfish wrote:
Well, if a 350 powered Jag bugs you,
Aaggh, I never said they bugged me, I just didn't understand the need.
Very cool car BTW
So, am I to understand that you are bothered by V8 Jags then?
They are Ford V8's afterall... 
Adrian_Thompson wrote:
OK, the cool XJS advertised on CL in another thread got me thinking. Honestly why are there so many Chevy powered Jags out there?
'Cause someone made a book about it.
Remember: a Chevy 350 will run like crap longer than most Jags will at all.
spitfirebill wrote:
Any boob can work on a chivvy.
Well, any boob can work on them, but from what I have seen, a lot of 'em are really bad at it...
Having owned a Jag XJS V12, I can tell you the "eclectics" going wrong isn't something that just affects the hoses and wiring. For example, the factory greased the distributor with something that got hard, freezing the advance mechanism and causing the car to overheat. Warped heads meant repairs that were about 3x the cost of a LBC swap. Also, the fuel injector hoses would bake hard and split, spewing fuel onto the sparking distributor causing an engine fire. The 12 was unbelievably smooth and powerful, but the Rube Goldberg vacuum and ignition systems made it tough to keep it that way. And on and on.
I've found that most of us Americans don't understand the way the Brits did things and instead of learning just swapped to something they knew. Personally, I find the Jag I6 is one of the purtiest engines made. Have a friend with a Jag with a SBC swap. When it runs it runs well. But he constantly has issues with it, mainly the fuel system. Twin tanks on the XJ6.
Same goes for SU type carbs. Us 'mericans only know downdraft so that's what we swap to.
Caveat: above doesn't apply to us.
wlkelley3 wrote:
I've found that most of us Americans don't understand the way the Brits did things and instead of learning just swapped to something they knew.
I'm combining the observation above with the history of tuners of British motorcycles having trouble with how many places after the decimal Japanese motorcycles had their tolerances specified to, and wondering how we here in the states ever came to develop industry more sophisticated than the production of baby food...
I heart the Jag V12's and the earlier 4.2 six shooters. Wonderful engines. Make all the right noises, plenty of power (at least for their era) and in gorgeous cars. Now, having said that: my dad had 3 XJS's and all 3 spent a LOT of time under the knife. When you have to depend on something daily, that's not good. I keep threatening to find a non running XJS and V8 ify it, of course I'd do the 2.88 rear axle swap too, keep the RPMs down at highway speed. I would damn sure do fuel injection, I am sick of carbs on daily transport.
As far as the engine itself, forget the usual SBC/SBF. Being the contrary bastard I am I'd do a Lexus V8. Might leave the slushbox behind it, but a R154 5 speed is a strong possibility as well.
wlkelley3 wrote:
I've found that most of us Americans don't understand the way the Brits did things and instead of learning just swapped to something they knew.
I see this attitude in the rotary world as well.
The idea that you only dislike something because you don't understand it is nothing more than the corollary to the Stockholm Syndrome. As has been pointed out upthread, while Jag engines may have thrived very well where it doesn't get hot and "pollution control" means you try not to spill more than half of the petrol before it gets into the tank, they didn't fare so well here. I do seem to recall that American automakers also ran into thermal issues head-on in the 70s when trying to clean up emissions. Jaguar was also certainly not the only non-US automaker to have heat related issues in the US. Porsche had issues too, for one example off of the top of my head. (So did VW, but ACVWs always had issues even before emissions controls get factored in)
And, Jaguar has had a history of not thinking their cunning plans all the way through. My favorite example: Jag engines test-fired on natural gas after assembly but before shipment. Natural gas cleans the valve guides of lubrication. Valve guides get sticky in storage, leading to bent valves upon first crank after installation.
There's also questions of availability. Americans aren't "afraid" of SU carbs, they are just hard as hell to find parts for around here. It's not much different than, say, people putting Volvo strut suspensions under American cars in certain countries. Go with what you can source.
Yeah, local availability is a big thing. There's a bunch more SBC's than Jag V12's laying around. But that in itself is not a good reason to do such a swap.
Honestly, the garden variety SBC (the pre-LS) is not even faintly exciting to me . Ho hum. Yeah, I know they are everywhere and there's a metric E36 M3 ton of aftermarket for them yada yada but damn they are just so... pedestrian. The LS is an improvement (a BIG one!) but still doesn't fire my imagination like a DOHC V8. Or a rotary.
In reply to Curmudgeon:
Most of the swaps I've seen were done in the late 80s early90s. It was seen more as a way to get a nice running luxury car than a sporty performance car.
Wally's right, a lot of them were done for that exact reason. At the time you could buy a low mileage Jag with problems cheap, do the swap and drive a nice set of wheels for 10 years with minimal work. Well, other than the remaining Prince of Darkness stuff. 
It was pretty widespread; I can think of at least 4 or 5 down here in the Armpit of America.
FWIW, there is an '83 XJS on the local CL that keeps dropping. Last I checked (this morning) it was at $1200.00. NMNA...
http://columbia.craigslist.org/cto/4599745537.html
I bet if I waved $900 at him... naw, I got another iron in the fire right now.
Why chevvy V8 when 2JZ-GTE...
Putting a 2JZ-GTE in an XJS...
The question isn't "Why would someone want to put a 350 in a Jag?"
The question is "Why would someone want a Jag?"
RoughandReady wrote:
The question isn't "Why would someone want to put a 350 in a Jag?"
The question is "Why would someone want a Jag?"
You drive a diesel Benz, all your arguments are invalid
I wouldn't do it to a straight 6 Jag but a V12 Jag I can understand. Impossible to work on is being too kind.
How reliable are the AJ16-powered Jags ('94-'96 XJS, '94-'97 XJ6)? I keep hearing that they're way better than the earlier ones, and also better than the later V8 (Nikasil) Jags, but the people I hear this from are Jaguar apologists.
They're so beautiful...and I'm so bad at troubleshooting electrical issues. That's a bad combination.
Here are some good uses for the swap leftovers:
http://www.v12designs.co.uk/products/
'Course, that's the block under the table on Top Gear, as well.
Some time ago I saw some on the web that included a lot of the ancilliaries painted in different colors-- beautiful! Unfortunately, SWMBO, while being appreciative of much auto art on the walls, draws the line at car part-based furniture.
Adrian_Thompson wrote:
RoughandReady wrote:
The question isn't "Why would someone want to put a 350 in a Jag?"
The question is "Why would someone want a Jag?"
You drive a diesel Benz, all your arguments are invalid
I have a buddy who is in love with English rides. I'm in love with never fixing things.
