one problem. im in the U.S. and even though the L67 is a U.S. engine, they were never offered in RWD in the U.S.
running an L67, which i would like to do, in a RWD car requires different oil pan, different flywheel, etc. The L36 was offered in RWD with MANY differences, but im not sure if i could just swap out the oil pan, and the flywheel to make it work. the bellhouse pattern is probably different too.

my built T400 will bolt up to my pontiac 307, and my buick 455. im pretty sure it BOP bellhouse pattern.

 

Not trying to derail, but I'd like to see a clearly delineated path (in stages) to upgrade a V12 XJS to modern HP levels.

I also follow the Porsche 928 forum at Rennlist. These guys have it down to a science:

- make sure your car is in fine fettle
- rear muffler bypass
- cross pipe
- headers
- tune (sharktuner)
- complete SUPERCHARGER or Twin Turbo kit (have you SEEN Fran Kuhn's kit????)

My own thoughts on the XJS progression go like so:

- make sure your car is in fine fettle
- get a modern transmission in there!
- intake & exhaust
- ECU & ignition
- twin turbo kit

Links to some of the 928 stuff:

Kuhn Performance Technologies :: Twin Garrett GT2871R turbochargers

928 Porsche® Superchargers and Supercharger Kits

The ONLY source for 21st century power for your Porsche 928

928 Specialists - 928 Supercharger Kits

With the exception of that beautiful twin turbo kit (~ $15k), the supercharger options all run <$6k (labor not included), and will put down 400+ RWHP.

I can't be the only person here who would be willing to drop $6k + mechanic's labor into a well-sorted XJS kit to get some serious ****-eating grin power. Can I????

 

drfinately not the only one.

 

We got both the L67 and L36 here in RWD only and through considerable research ( I was originally looking at this engine as one option for my XJS- another story) the block, crank, cam, rods and heads are the same part number, the L67 heads have injector bosses machined into them. The pistons are different.

I understand you are researching I do the same - I think you need to decide what you want the car to do and how much you want to spend - the XJS is not cheap to modify. I know I have dropped $4k of PARTS only into my rear suspension, including front shocks and rear end powder coating.

Changing the rear ratio has taken 3 months and is still under way. The hemisphere is almost impossible to get so I have had a spacer made 3 times when they fix the last one. Going GM for the drive train would be far cheaper than retaining the V12.

cheers
Warren

 

i dont want to change the rear ratio. im rocking 2.93's in my L67 powered car and im loving it.

also, the valves are bigger in the L67 heads as opposed to the L36. the L67 has 1.8:1 ratio rockers while the L36 has 1.7:1 ratio. everything from the top end up is totally different, heads intake manifold, throttle body, etc. only thing different in the bottom end is the pistons. L67 is 8.5:1 and L36 is 9.4:1 compression. L67 has 32 pound injectors while the L26 has 20 pound injectors.
the L67 is ideal for large boost applications, while the L36 is better for an all rounder with modest boost.
weve been debating on my Grand prix forum (L67 based) as to whether or not you can run aftermarket heads for a buick grand national on our engines. it hasnt yet been decided.

 

I know we are bit off topic here, the L67 we got here had 1.67 rockers from the factory not 1.8 so as Aus is such a small market I bet GM here used the L36 and just added a SC and US L67 pistons. The guys that had the turbo L67 ran a set of alloy heads from the US and they did not work well, don't know what the final outcome was though.

The ratio change has set me back about $800 for crown wheel and pinion and spacer, the rest of the parts are bearings some of which are unique to the Jag.

My XJS had 2.88 and quite a healthy engine but with the weight it was quite lethargic off the mark. Almost anyone you talk to who has one will testify that the 2.88 is woeful for spirited getaways unless you have 600+hp.

 

like i said, ive got 2.93 in my grand prix, with a 4 speed. i spin the tires if i go WOT in first gear, even if i just ease onto it. of course, im sure it has a lot to do with my first gear ratio as well.
i would rather change transmissions then change final drive ratios. my grand prix runs 1700RPM at 70 miles per hour, and i get a little over 40 miles per gallon. im running 232 WHP with my 3.4" pulley, my split ratio rocker arms, my DIY ported and polished blower and LIM, and a colder set of plugs.

the XJS is only 500 pounds heavier than my Grand Prix.

 

Another route if an XJ-S is imperative but a V12 is not is to go down the XJR route. XJ-S (V12 or 3.6) as a starter, a rusty XJR donor and you are well on your way. I have been thinking along that route for a while but have another project to do first.

 

Per, I do not see how swapping an XJR drivetrain could possibly be any more economical than the well established lumping procedures (small or big block chevy, LS1, etc).

Am I missing something? Genuinely asking.

 

i dont understand either. i mean, it would be fun, but it would be just as expensive.

 

You would retain the Jag link using another Jag engine. All simple things like engine and gearbox mounts etc etc would fit with ease (mostly staright bolt in). And at least in Europe getting a rusty XJR X300 and fitting that would be way cheaper than any V12 tweaks, and probably cheaper and a lot simpler than lumping. Finally it would retain its value better, lumps are a big loss compared to what you put into them. Shipping an XJR UK -> US west coast would be (guesstimate) USD 1500,-

 

It would be much cheaper to swap in a lsi twin turbo it or sc over anything else for that kind of power. Even na it will easily beat the jag engine for way less money. There is tons of eaftermarket support for chevy and sb,bb,or ls1 with stand alone engine management. Just trying to swap in a later xjr engine and drive trian would be anight mare, youll need abs, tcm, ecm, acm, i pack, everything comunicates on the can network and they will all be looking for needed messages and signals for operation. I can guarantee youll long run out of money and patience before you ever get this rolling, and that would be if you aquired a donor car for all harnesses and modules. You can my a stand alone wiring harness for ls1's style engine or many other popular fuel injected combos from painless wiring, street and performance etc....
Hands down youde be money and fewer grey hairs ahead. I wouldnt mind doing a v12 build, but if it was money and simplicity issues. Ide be doing the gm or even ford route all day long

 

BRUTAL,

From what I've read, the two major players in the engine swap kit business are John's Cars and Suncoast Conversions. John's appears to be more comprehensive and thus more expensive. Based on their website, they cover all XJS models.

Jaguar conversions, swaps, parts, service and advice - from John's Cars in Dallas.

SunCoast Conversions website:

JAQUAR V-8 CONVERSIONS

 

all good advice, BUT seems to miss a very important thing, a V12 powered car is very smooth runnin, and nothing can make the exhuast SOUND of twelve cylinders.

part of the reason i like cars is the sensation of driving and subtle show off rights.

a V12 with a manual transmission is an encredible thing to drive, you can actually stop with engine off,put the trans in 4th , turn the key and accelerate smoothly away.

try that with a V6 or V8!

now if you are gonna make a race car, you gotta go V8,USA style.
and another thing, today, if it aint forced induction, it aint cool!

i'm a street car guy, serious racing is to expensive!

 

V12?? count the power impulses each engine revolution, one fires and the next pulse is right behind it= SMOOTH as silk, V12 is naturally balanced in all vibrational harmonics,.

long endurance race drivers say they always feel better after a long time race.

and torque impulses dont tear the car up as easy!

kot to be said for 12s,, but to each his own.

 

On your shores how much would a lsi twin turbo be complete with all the bells and whistles? Here in Europe I could source a rusty / tatty XJR with good mechanicals for about USD 3000 and just about move everything over as one going concern. Personally I stay with the twelves.

 

YES BUT I BELIEVE THEYRE STILL OLD SCHOOL , FOR LS CONVERSIONS IN JAGS GO TO THIS WEBSITE
Jaguar Specialties

 

THIS. thats the single, solitary reason i havent put more thought into swapping in my 455. i want a V12 because i want one. shame its so much more expensive.

 

The clips of XJS exhausts I've heard have all been underwhelming. If you have something outstanding to share, by all means, post a link.

That said, I will be removing the forward set of mufflers & replacing the rearward set with some Borlas or Magnaflows. Will make a professional recording and share.

 

A cursory search of ebay shows plenty of complete LS1 engines less than $2k. I don't know how much it would cost to twin turbo.