When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I just pulled the V12 out of my XJ-S.
Why? because I bought the car 6 years ago with new head gaskets fitted. The guy I bought it off had not finished plumbing or wiring it up.
Looking at all the perished bits of rubber and disconnected stuff that I have no idea where it should go the decision was made. I'd rather drive the car than look at it with an inactive V12. For ease of being worked on I'd put it as being as enjoyable as a Renault or Fiat ie a lot of "What were they f%$ing thinking when they designed that".
What's going in? A 4 litre DOHC Ford Barra engine. At 195Kw it's 25Kw shy of the original V12's 220Kw but it's 200 odd Kg lighter. Barra engines also came factory turbocharged. The most mild Barra Turbo is 240Kw and they went up from there. Even the 190Kw can be improved a decent amount by improving inlet and exhaust flow
If the 4.0 proves too tall then plan B is a 3V 5.4 Ford V8. If that won't work plan C is an LS1 however I don't like their crackly farty exhaust note.
Just for the sake of debate people have been putting small block Chevs in other cars for years due to obvious benefits.
"I'm going to put a V12 Jag engine into my (insert make and model here) due to reliability, fuel economy, power and ease of maintenance gains" said no one ever.
Last edited by Jim5_0; 10-13-2020 at 04:51 AM.
Reason: typo
Yes, I'm a purist. Still can't understand why someone would want to go through all the trouble of swapping someone else's engine into an XJS when he could buy a perfectly good Camaro (or a Mustang, but nobody talks about putting 4.6-4Vs into XJSs), save himself the shop time and the headaches and go driving.
Top Fuel Hemis have a life expectancy of...what? And that after 60+ years of no-expense-spared development? Any BBCs (or LSs) running in Top Fuel these days? If not, why not? Bruce McLaren had 650+HP aluminum-block 494 BBCs that would last a whole Can-Am race before the block warped to the point that they couldn't be rebuilt around 1970. For that matter why not use a V12 aircraft engine like an Allison (unlimited hydroplanes did)?
Think one of those 10,000 HP Hemis could run the Le Mans 24, or would it detonate after the first lap? The horribly unreliable Jag V12 somehow got one or two overall wins at that event. I don't think an LS motor has done that yet. SBF's done that, BBF too, but not many of those going into XJSs for some reason or another.
Hemi cylinder head is a copy of the P&W cylinder heads from the engines Chrysler built for Ford's B-24s.
IIRC, Bob Tullius won two Trans-Am titles with Jag V12s, once in the XKE and once in the XJS. Might he have beaten a Detroit V-8 or two in the process? Naaaaah, couldn't be, eh? He then won a race or two in IMSA GTP with the V12, and when he lost, generally he lost to Porsches rather than to pushrod engines of any sort.
Bigger Merlin was called a Griffon. Went into Spitfires late in WWII, Avro Lincolns and Shackletons afterward.
P-38s didn't work out in ETO because RAF controlled the fuel supply and saved all the good stuff for themselves. Turbo Allisons needed reliably 100 octane fuel, not "we say it's 100 octane, and pump it through a rag to knock the big chunks out before you fly" 100 octane. P-47s with their turbocharged R-2800s were more tolerant of junk fuel. Now, wait a minute, did that mean that the Allisons were unreliable, like a Jag V12? In the Pacific, USAAF controlled the fuel supply, so the P-38s got the good stuff, ran fine and destroyed the enemy. How could that have been? Didn't we just prove them unreliable, like a Jag V12? Oh, wait a minute, maybe they weren't unreliable, just mistreated. Kinda like a Jag V12?
Canadian Mosquitoes got Packard Merlins from Detroit. Didn't think AUS went through with building Mosquitos because the wooden construction wouldn't stand up to the climate in the South Pacific - USN had the same trouble with PT boats. Had they done so, I'm sure they would've used Packards from Detroit - shorter trip than from Ford UK in Dagenham. Oh, you didn't know that, though they said "Rolls-Royce" on the valve covers, they were built by Ford in Dagenham, home of the Cortina and Formula Ford engines? I think AUS-built P-51s got Packards, but post-war.
Here are some nice high res photos on Bob's machine.
/
I'm not sure what your point is in the context of the present day. No-one here is racing in Trans-Am or fighting WW2 at this point.
Everyone is free to do what they want with their car as they see fit so long as it's legal. Criticize them on the details to execution if you want to... but that criticism should be fair and somewhat germane.
It's kind of trope at this point to suggest the Jag V12 was mis-understood and only fails because they were not maintained or misunderstood. I might suggest the measure of good design rests in is resilience against abuse. To borrow your WW2 reference, Pilots loved the B17's becasue they could take abuse above and beyond what was reasonable for foreseeable and you'd get back to base... god willing. Machines and by extension their designers are appreciated for their what their designs can do beyond what they were designed for and what would have been foreseen.
You certainly are free to put whatever engine you want on n whatever car tickles your fancy. Cost be darned. Pros want $20,000+ to do a complete job putting a Chevy V8 in a Jaguar including sorting out the resulting car. ( I hope)
For that same $20,000 plus whatever your Jaguar is worth there are a whole lot of choices. ( including newer Jaguars). And for what it’s worth Chevy’s often need work too!! Otherwise they’d get rid of that service department.
I’ll continue to race Jaguar V12’s and Jaguars in general because they are much more durable engines on the race track than Chevies. While Chevy makes a good car, ( I’ve bought 19 New Chevy’s in my lifetime) But for racing they don’t hold up unless you replace everything in the engine. Everything!
I’ve raced Jaguars where I had less than I spent for my first new Chevy ( 1972 Vega GT ) in the whole car. I also tried to race cheap Corvettes etc and never actually finished a race except on the tow rope.
What Chevy has is a well established group of Monkey see Monkey do mechanics. The fact that a Jaguar is a mystery to most people should tell you about most people rather than anything negative about Jaguars.
,Pawns,, some interesting knowledge about WW2 and the GREAT ALLISON engines, shame how a country we were helping would not agree
with original designers, and actually took the turbochargers OFF the engines and run them NA , saying they had not enough power!
and some place i read that the pilots in the country , would argue over who got the Packard-Merlin built in there planes!
The fact that a Jaguar is a mystery to most people should tell you about most people rather than anything negative about Jaguars.
That fact is exactly what is wrong with the V12. The engine itself is great. All the ridiculous and complicated add ons fitted to a road going V12 are what makes it bad. Break down in the desert and what are your chances of the local roadside assistance guy getting you going again?
Fuel rails? Who needs those when we can just put a spaghetti nest of rubber hoses all over the engine ready to split and burn the car to the ground.
Why have one top radiator hose to blow and leave you stranded when we can have two instead of a metal coolant manifold connecting the heads to the radiator via one hose?
I agree that to make a Chev small block strong, reliable and fast you first have to empty the engine into a garbage bin and buy all new internals. Those internals are readily avaialable.
Outside of the Americas a Corvette, Camaro, Firebird, Mustang etc is a rare and quite expensive car but their engines are neither rare or expensive.
"I'm going to put a V12 Jag engine into my (insert make and model here) due to reliability, fuel economy, power and ease of maintenance gains" said no one ever.
Not quite true
A few years ago I converted an XJ6 into an XJ12 and use it as my daily driver. It has 100hp more than the 6-cylinder, uses the same amount of fuel, and has been quite reliable. It was a fun and easy project. I'm 100% satisfied with my decision.
Mind you, I have nothing against V8s. In fact, most of my life is centered around repairing old muscle cars,Corvettes, and the like. I love 'em.
That fact is exactly what is wrong with the V12. The engine itself is great. All the ridiculous and complicated add ons fitted to a road going V12 are what makes it bad. Break down in the desert and what are your chances of the local roadside assistance guy getting you going again?
Virtually nil.
If you have an old Jag V12 you have to be self-sufficient. Or be prepared for a huge towing bill to a (few and far between) specialist, if you can find one who knows V12s....which isn't always easy.
As for the spaghetti of add-ons, soon enough it becomes nothing. Once you understand what it does and why it's there, 'tis no big deal. But, you gotta enjoy the learning part. If not, you're sunk.
A Jag V12 isn't the right choice for everyone, that's for sure. But it's exactly the right choice for some.
For others, a SBC or other swap is the right (or most enjoyable) decision.
If you have a hobby/project car and it makes you smile, you've hit the right combination no matter what engine you choose.
That fact is exactly what is wrong with the V12. The engine itself is great. All the ridiculous and complicated add ons fitted to a road going V12 are what makes it bad.
It's a fair point. Jag V12 was not designed to be practical for road use. The block, metallurgy and oiling system is right from the race track From the heads up it was built to a price and compromised. The early V12 had 4 carbs.... Early SBC and Cadillac V8's had 1. Their-in lies the root of problem, complexity and for the Jag V12 it was somewhat un-necessary. 4 times as many chances to have a problem that renders the car in need of repair and 4x the touch point when that need for repair turns into diagnostics and replacement. When Fuel injection came along that number when to 12,, early GM fuel injection systems had 2 injectors. Due to the constraints of time and knowledge, when a mechanic touches something the chances are greater than Zero that its compromised in some way, That adds up over time. Cadillac V8's of the day were nearly as smooth, and many of the virtues of a V12 can not be experienced with an automatic transmission.
Personally speaking, I'm fascinated with the tenants of reliability, my career depends on it becasue I install and sometimes build servers and PC's for businesses. The one thing I learned long ago... simple is better, less is more. I've walked into many companies with reliability issues over the years and replaced their bank of servers with a single but carefully selected or built server. Fewer problems and easier to diagnose where the issue lies when a problem occurs. Usually I find a small mis-configuration or reliability issues with one of the servers that ends up effecting the others leading to frustrating outcomes. Same scenario with cars often occurs, one item effects the others, the more items you have the more potential problems.
Same thing happened in WW2, German planes had complex port fuel injection systems, the Allied planes by the mid 40's mostly used a simple and early form of throttle body injection, a single fueling point. As a result Allied planes were easier to repair and spent more time in the air.
Complexity personal or mechanical may be intriguing but over time becomes unhealthy and inconvenient. Rube Goldberg understood this fascination with complexity. Same holds true today so the future is clearly simple and full electric.
Last edited by icsamerica; 10-13-2020 at 10:11 AM.
It's a fair point. Jag V12 was not designed to be practical for road use. The block, metallurgy and oiling system is right from the race track From the heads up it was built to a price and compromised.
If Jaguar had put as much thought into heads and cooling system as they did the reciprocating assembly....well, we probably wouldn't be having this conversation
The early V12 had 4 carbs.... Early SBC and Cadillac V8's had 1. Their-in lies the root of problem, complexity and for the Jag V12 it was somewhat un-necessary. 4 times as many chances to have a problem that renders the car in need of repair and 4x the touch point when that need for repair turns into diagnostics and replacement.
Jaguar motto: "Never use 6 parts when 10 will do the job perfectly well"
Personally speaking, I'm fascinated with the tenants of reliability, my career depends on it becasue I install and sometimes build servers and PC's for businesses. The one thing I learned long ago... simple is better, less is more. I've walked into many companies with reliability issues over the years and replaced their bank of servers with a single but carefully selected or built server. Fewer problems and easier to diagnose where the issue lies when a problem occurs. Usually I find a small mis-configuration or reliability issues with one of the servers that ends up effecting the others leading to frustrating outcomes. Same scenario with cars often occurs, one item effects the others, the more items you have the more potential problems.
Naturally.
So much depends on what you want out of a hobby car and what your expectations are. I have zero expectation that my 35 year old hobby car, which is also my daily driver, will go months on end without needing attention of some sort. That doesn't bother me. If it did, I'd buy a late model drive-it-and-forget-it car.
The V12 experience is very satisfying to me but I can see where it wouldn't be for the next guy. And, to be honest, I'm contemplating my next project car and it'll probably be something without climate control, power accessories, and so forth. After owning several Jags over the last 23 years I've spent much more time fussing with the cars than I have with the engines. That is, taken on the whole, I've spent a lot more time and money on non-engine-related issues than I have on engine-related issues. An engine swap alone doesn't ensure a trouble-free relationship with an old Jag.
I think another MG might be in my future. Or maybe a TR6. Or....an old Corvair !
Complexity personal or mechanical may be intriguing but over time becomes unhealthy and inconvenient.
That comes down to the person. Life can be complicated, and I'm a worrier. When I need to clear my head I turn to my Jaguar for some meditative and peaceful tinkering
JIM5 fuel rails and the jag setup, didnt set well with me!
so just a simple redesign using cheap honda injectors, made up a set extruded aluminm rails, with Neoprene O-rings top and bottom and Aeroquip fittings/lines!
i pressure tested to 300 PSI air , no leaks at all, nothing in 26yrs !
also a GOOD fuel pressure regulator! adjustable fuel regulator. custom fuel rails and lines.
also the rail was from a scrape metal yard , 10ft long cost me 10 dollars!
ron
It's a fair point. Jag V12 was not designed to be practical for road use. The block, metallurgy and oiling system is right from the race track From the heads up it was built to a price and compromised. The early V12 had 4 carbs.... Early SBC and Cadillac V8's had 1. Their-in lies the root of problem, complexity and for the Jag V12 it was somewhat un-necessary. 4 times as many chances to have a problem that renders the car in need of repair and 4x the touch point when that need for repair turns into diagnostics and replacement. When Fuel injection came along that number when to 12,, early GM fuel injection systems had 2 injectors. Due to the constraints of time and knowledge, when a mechanic touches something the chances are greater than Zero that its compromised in some way, That adds up over time. Cadillac V8's of the day were nearly as smooth, and many of the virtues of a V12 can not be experienced with an automatic transmission.
Personally speaking, I'm fascinated with the tenants of reliability, my career depends on it becasue I install and sometimes build servers and PC's for businesses. The one thing I learned long ago... simple is better, less is more. I've walked into many companies with reliability issues over the years and replaced their bank of servers with a single but carefully selected or built server. Fewer problems and easier to diagnose where the issue lies when a problem occurs. Usually I find a small mis-configuration or reliability issues with one of the servers that ends up effecting the others leading to frustrating outcomes. Same scenario with cars often occurs, one item effects the others, the more items you have the more potential problems.
Same thing happened in WW2, German planes had complex port fuel injection systems, the Allied planes by the mid 40's mostly used a simple and early form of throttle body injection, a single fueling point. As a result Allied planes were easier to repair and spent more time in the air.
Complexity personal or mechanical may be intriguing but over time becomes unhealthy and inconvenient. Rube Goldberg understood this fascination with complexity. Same holds true today so the future is clearly simple and full electric.
Those 4 carbs are as simple as a lawn mower carb and very seldom the problem. Plus those 4 carbs flow as much as a Holley dominator without the complexity of the Holley dominator
As far as complexity those German engines with their fuel injection didn’t have the flaw the Rolls Royce engine did with their carbs. In a negative G situation( frequent in combat) the carbs would stall out, not something you want your engine to do when fighting to the death.
HI Doug, you mention Jaguar engineering of the V12 cooling system, ( I saw a few Jag V12s at the Daytona 24 races few yrs back) , as i remember a least 90% went down DNF, because of overheat/blown head gaskets!
i made some personal tests to see how much coolant the heads would hold, a stripped bare V12 head(left the guides in place), was very little coolant liquid!
so me being me DUH!
i set my two heads up bare on outside wood saw horses, flat side up, slowly poured raw undeluted Muriatic acid into coolant jackets, they boiled and fumed/and gurgled, for at least 1/2 hr!
the crud that boiled came out ,chunks of aluminum debris. ugly casting crap , and unidentfied junk, even pieces of jacket walls!
i dont recomend this for many guys, but when finished(about an hour each), i flushed heads with a 50/50 mix of Sodium bicarbanete, flushed them bare next day,!
tested internal jacket volume again and 1 1/2 cups more water than factory stock ,, i have no idea if it helps cooling but cant hurt holding more liquid coolant!
i'm outta the box again sorry, i'm from a different generation and seems a i think differently!
ron
"I'm going to put a V12 Jag engine into my (insert make and model here) due to reliability, fuel economy, power and ease of maintenance gains" said no one ever.
And yet I have seen photos of a Jag V12 put into a Corvette. Naturally it horrified the Corvette guys that someone would "contaminate" a Corvette with anything other than a Chev engine, yet they seemed to think nothing of ripping a Jaguar engine out of a Jaguar. Most odd.
Apparently this Corvette was from the height of the emissions era and the owner wanted more power than whatever gutless SBC was in the car, and something different. LS swaps are a dime a dozen, V12 swap not so much.
OK, SBC guys, what did this guy do wrong? Doesn't sound like an LS...https://www.facebook.com/1276914270/...88983/?__cft__[0]=AZV76H4CqqEoLzEGh8pAlwwwxmwbK0-QVhEQWR4qTrpXw59Pzfi4Pg6aQaO-yI5f-d4a6uNUS5SeOdNfl9qHhfHTatnRY8veEEk7oKUPwgFFn7QUUO0 Cp5933wIBGcJETV4KTTgrMummoZFrcm_qehb5t8px5rb1sBMGC 9j5Y9F80Epag7Fw6i7FbXx1ErWKcn_Ktp6NkkOuPqQZ8dZJokd g&__tn__=*bH-R
HI Doug, you mention Jaguar engineering of the V12 cooling system, ( I saw a few Jag V12s at the Daytona 24 races few yrs back) , as i remember a least 90% went down DNF, because of overheat/blown head gaskets!
i made some personal tests to see how much coolant the heads would hold, a stripped bare V12 head(left the guides in place), was very little coolant liquid!
so me being me DUH!
i set my two heads up bare on outside wood saw horses, flat side up, slowly poured raw undeluted Muriatic acid into coolant jackets, they boiled and fumed/and gurgled, for at least 1/2 hr!
the crud that boiled came out ,chunks of aluminum debris. ugly casting crap , and unidentfied junk, even pieces of jacket walls!
i dont recomend this for many guys, but when finished(about an hour each), i flushed heads with a 50/50 mix of Sodium bicarbanete, flushed them bare next day,!
tested internal jacket volume again and 1 1/2 cups more water than factory stock ,, i have no idea if it helps cooling but cant hurt holding more liquid coolant!
i'm outta the box again sorry, i'm from a different generation and seems a i think differently!
ron
Ron that’s brilliant. An easy way to ensure the heads are clear of junk. Without a deck it’s very easy to check if all the crud is out of the block once the heads are off, but that method will definitely at least make me feel better. ( even if I don’t get the results you did )
One thing I’ve also learned is that often water short circuits. It’s pumped in at the front of the engine and allows coolant to exit anyplace along the water rail.
what I did on my race cars is basically reverse the water rails. Allowing water exit at the back of the motor. Then I restricted water flow towards the front. Yes I made custom rails and they were lighter and much neater looking.
My thoughts after reading the whole thread. You buy a V12 XJS because:
A. You want an XJS. One or more things about the car does something for you. It may be the styling. It may be the interior. It may be the V12 engine. It may be the overall driving experience.
B. You want a Jaguar, and an XJS may be the one that fits your price point. It is one of the cheaper Jaguars you can buy.
C. You want a V12, and an XJS fits your price point. A V12 XJS is the cheapest V12 sports car you can buy. You might also find a BMW 7-Series or Mercedes S-Class luxo-barge in the same price range. The M70 BMW engine is roughly similar in terms of performance to a Jag V12. The M120 Mercedes starts with about 100 more horsepower, but you get it in a car that weighs only slightly less than the Titanic, unless you get an R129 SL600.
I happen to fall into C. If I had loads of money, I would have bought a V12 Ferrari. I don't have loads of money, so I got a cheap Jag. To me, stuffing a V8 in it would be missing the point.
If I simply wanted a nice V8 car, I could have bought a Corvette. Or a Camaro. Or a Mustang.
If I just want to go as fast as possible for as little money as possible, I can go on Craigslist with $4000 and get a decade old literbike and go 186 mph on the way home. I already have a good used Triumph Street Triple that will beat nearly any race-prepped XJS from 0-100.
I can understand why some people might do a V8 in an XJS, but I would never do it. M120 swap, unlikely as hell, but just a bit possible.
10-11-2020 | 11:27 PM
