Hi!

Does anyone have any experience doing that?

thanks!
-aa

 

I have lots of experience personally and many others here do too. There are many advantages to doing a Chevy conversion. Less weight and more power in most cases, lower fuel consumption, and greater serviceability and reliability. The reduction in weight over the nose significantly improves handling, braking and acceleration. The torque of the chevy motor plays well with the tall gearing of the pre-facelift V12's.

There are many pitfalls with doing a conversion. The person doing the conversion must have good mechanical and electrical skills to get all the fine details like gauges and A/C working properly. If done well the conversion has the potential to increase the value of the vehicle significantly. If done poorly or incompletely the vehicle will be worth almost nothing.

At this point you have little chance of selling a conversion for more than the cost to do the conversion unless you got some of the parts and labor for free. The market for XJS' converts just isnt there...yet. Converts are most appreciated by someone who already has one so they have a somewhat muted appeal broadly speaking.

Currently, there is still a lingering stigma associated with converts among the purists. Some here have cowed those that have broached the subject like you have. Dont be deterred, the tide is turning. As time goes on the converted XJS' are becoming more tolerated as more of the die hard purists experience catastrophic engine failures. XJS converts are not yet as embraced as the converted XJ coups and sedans. The reason for this is rigid idealism combined with the fact that many converts are incomplete or very poorly done. There is something to be appreciated when it comes to originality and a conversion certainly destroys "originality" significantly. But, if your V12 is a spent bomb and the ability or willingness to fix isn't there, then conversions can keep these cars on the road and out of the crusher. That said... there are some people so rigid they sleep standing up and would rather see an XJS get crushed than converted. Wont be long till they make themselves "prone" in subsequent posts.

A Chevy conversion is a GREAT way to turn the XJS into the sporting GT it could and should have been. A LT1 with a 6 speed is an awesome and low cost way to create a very refined and unique GT experience that offers a very high level of performance. The LT1 or LS with a 4l60e is great for those who dont want to row. The TPI /700R4 package offers a vintage performance feel which still performs well and is still appreciated by many and a good low low cost approach if you already have one. The 350/350 conversion or SBC with carburetor and 3 speed TH350 transmission is passe at this point.

So... if you're going to do one... do the car justice and do it as right as you can. Unless you're an accomplished fabricator, it would really help to speak to Andrew from Jaguar Specialties. If you follow his program and kit you will have a greater chance of completing a well sorted convert that is reliable and a joy to drive.

Dont get carried away...unless you really want too. You could easily spend 7 to 15 grand on an LS engine alone... This type of conversion can overwhelm a stock suspension and chassis and put a big dent in your wallet. This type of engine can also offer a high level of over all performance if you are willing to spend the additional monies necessary on larger wheels and tires, suspension, brakes and so on. An LT1 conversion can cost as little as $3500 and is a great match for the capabilities of the stock suspension. The Lt1 offers a few more horsepower than the V12 but far less weight, therefore over all performance is much higher. LT1's can be massaged to make almost the same HP as entry level early LS1's. The LS and LT1's with their sequential fuel injection offer levels of refinement very close to the v12. Basically if your conversion is an exercise in frugality the LT1 is the way to go. If not the any LS is a great performer and would have more refinement and a higher resale becasue, these days, almost anything with an LS is sexy.

 

There are many thoughts on such conversions, and part of it will depend on what your goals are for the car. If you ever want to show it at a JCNA show it must have a Jaguar engine for example.

I would never do a conversion if saving money is your goal. The cost to do a conversion properly and have everything working with almost always exceed the cost of fixing the original engine. The V12 is a very durable engine mechanically, the most failure prone part is the GM ignition module. I had a sedan with the V12 and everything GM on it failed - the transmission, ignition, AC and power steering pump, while the engine kept on going. So don't buy into the myth that you'll never have any trouble if you go an all GM route.

So much depends on the quality of the conversion. I've seen some that were done in a single colour of wire for everything and crimp connections that made intermittent contact and corroded. The owner never could get it to run right. If very detailed notes of the wiring modifications are not kept with the car you're totally in the dark when it comes to troubleshooting too, as nobody can help you figure out what was wired to what.

There are pros and cons, but proceed with caution. If you want more power, then go for an alternative engine. If greater reliability is your goal, you might or might not achieve that. Unless you spend a great deal or are meticulous in doing it yourself, probably less reliability.

 

I myself am a halfpurist... I love the V12 engine and in a finely restored XJ-S the V12 looks perfect. It can be a daily driver but the V12 still needs it's care... Actually lots of care. And fuel

If I had two XJ-S', I'd probably lump one. Either with an LS or with an AJ26SC. But only if the V12 wasn't rescuable or it would cost more to do up...

A great looking senseful conversion, is of course to be favored. If you take say a small V8, example a Ford Windsor or so, which barely turns the crank (haha) it wouldn't be as clever.

Very important though then: Remove the V12 badge. You can count the brake caliper pistons of you want (as there would be 12 then) but that isn't the point of the V12 on the rear

 

Hi Daim

Yeah! the V12 is quite partial to a drop of Petrol now and again and again and again!....................

 

A good place to recite a manta, "to each his own".
I faced a decision in 2001. My very nice DOHC powered S3, conked out, big time. Came home from Stockton, Ca. on a flat bed. Ironicaly, Jaguar Heaven, a noted Jaguar recycler was within sight!!1


A limited knowledge diagnostic effort began with a compression test. "0" Never saw that before in any critter. Really bad news.


I did a lot of research and pricing. Fix or lump and if the latter, how.


Twasn't til 2006, that I got it to pass CA's stringent SMOG special referee test.


Back then, I wrote a "White Paper" on my adventure. Where is it now???


But, the LT1/ 4L60 E worked out exceedingly well. My install imperfect, and not asd pretty as some, but, better than a lot and it works. The Engine formerly resided ina big Cadillac Fleetwood Brougham. So, the tune status matches nicely. Torque vs HP needed. It's Lt2 pulls the .70 Of and the 2.88 Jag rear effortlessly.


I list this car among the top as my overall favorites of all eh cars I've owned or driven...


Carl

 

Hey! Thank you for this! I am in LA, can you recommend a good mechanic here? thanks a lot again!

-a

 

You don't say your reason for lumping an XJS. So here is my experience.

I have owned both my first Jag sported a 350 SBC and T350 it was a great car. I currently have a V12 XJS which I originally purchased to lump with LS1, but after driving it for a year decided to keep the V12 and that was 10 years ago. After a renovation (mostly body and suspension) it was my daily driver for 7 years. I still drive it as regularly as I can mostly long trips, it has never let me down.

So if your reason to lump is to save money then converting an XJS is not the way to go, it will almost certainly cost you more than bringing the V12 up to snuff. As said before the V12 engine is very robust and most of the issues are due to age / lack of maintenance these days.

If you are after the performance of a 500hp V8 then the best way forward would be to purchase an XJS that already is converted.

 

MY Jags need to have 12 cylinders - not diminishing any other models or preferences.

That said, I would entertain MY idea of an interesting swap, and that would include zero chance of a Chevrolet power plant. Some deserving (by my completely arbitrary standards) candidates have been floated here:

Audi V12 turbo diesel
'03+ Mercedes twin turbo V12
Toyota Century V12
BMW V12s
Ferrari V12s (sometimes they pop up cheap)

Seriously, go to eBaymotors.com and search "V12 engine" - the prices are really silly enough to try one of these. You would be a pioneer, as there's no prefab kit or support as for the Chevy. Meaning? A good conversion won't be cheap. A good way to recoup your costs would be to document everything and market your own conversion kit! In that case I'd go with the Mercedes twin turbo V12 setup

 

If I was going to do a conversion I'd love Jaguars 3.0 V6 diesel. I had one in a rental XF and it was lovely. 300hp, 516 ft-lbs at 2000 rpm and I averaged 47 mpg not driving it for economy.

It was interesting to have it on cruise at 70 mph and see the instant fuel economy in the 85-95 mpg range - it just sipped fuel!

 

I'd ditch it all and go 13B twin turbo... Or try and get a 20B, though sourcing one would be really hard... Buf then again, I'd turbo it as mich as possible...

 

there is an AUDI V12 diesel for sale in Seattle area, NEW never run except for testing.

this has been my dream since 2007!

factory stock makes 500HP, BUT makes 750 lb.ft.torque.

with a simple reflash of ECU ,can go to 700HP,, 1000lb.ft torque.

and in an XJS coupe, would easily get 40/50MPG because engine would loaf along without any load on it!

and like any good diesel the faster you go the better the fuel consumption ,for the miles travelled.

pro built 4L85E would be trans of choice ,5 pinion planetarys.

now all i need is money and time??

 

Had to look that up - rotary! OK why? I'm completely ignorant here - haven't been in an RX-7 (the one before they ripped off the 944) since the 80s.

 

OK gotcha covered , i was big into Mazda rotaries for 15yrs. 13b two rotor.

20B is three rotor,, 26B is four rotor

couple pix

 

The rotary is super light weight (everyone complains about how heavy the V12 is, so why replace it with another heavy V12?) very compact, hasn't got the torque in NA configuration but add a turbo or two or three and it is more powerful in torque than many other cars. It can takes loads of boost. It is abery flat engine and doesn't have any issues with timing difficulties.

A friend's RX7 NA 20B is putting 300 hp to the rear wheels... Ported and running on Mikuni carbs... So it has 300 hp at the wheels out of an engine running as smooth as a V12 with about a 10th of the weight!

 

Hmmm... obviously need to experience a proper rotary. Couldn't see myself doing it for such modest power gains though, even with the weight reduction (assuming you're exaggerating the weight difference).

If working with the V12, I think 400HP is a reasonable goal. If I'm lumping however, don't think I'd settle for anything less than 500HP coupled to a modern transmission.

ageyev, why are you considering the swap? This info will help us help you.

[edit] looked up rotary engine weights - they are light!

 

Nope. No exaggeration. The 13B weighs around 40 kg without alternator and AC compressor according to my friend. The V12 weighs without PAS pump, alternator and co something like 390 kg.

You can lift a 13B by hand into the engine bay on your own.

And the 13B is mildly tweaked at 300 whp. Stuff some turbos on it and you'll be seeing 800-1200 hp. The 20B will do somewhere around 1600 hp... And it only has a displacement of around 2l

 

My 86 XJS has a 350 V8 and I love it. More power and more reliable and easy to modify

 

.

you may be a little optimistic on your info!

a 13B two rotor bare engine ***., weighs in at 185lbs, with oil pan and front pully ,(i have weighed them), NO flywheel or balance weight!

a complete 13B with starter ,alternator, 2 manifolds, big turbo, and proper balance weight, flyw.clutch ***, intercooler ,piping , water pump, around 290lbs.

so quick numbers it is lighter than a Jag V12 by about 500lbs, thats a lot.

so power? my car dynod 420HP RWHP, 375 torque, 7500rpm. on 93 oct. street gas/petrol.

my 1987 RX7 weighed in at 2700bs, 1/2 tank fuel,no driver!

it ran 1/4 mile best 10.90s, 127mph, slicks. average 11.20s.

BUT? turbo rotaries are very fragile, break APEX seals ,blow coolant, overheat,ETC. with NO warning! contrary to what people think,THEY ARE NOT CHEAP TO FIX.
non turbo cant get out of its own way, 13B 120hp., altho you cant break them easily, tough litle suckers, and torqueLESS.

putting one in a tank like an XJS, 4100lbs,MINUS 500lbs, is a heavy 3600lbs of lead sled. fuel consumption would be BAD. rotories love fuel.

moving 3600 quickly needs at least 500+ torque, for both moving away from standstill, or passing at speed!

finding good three rotor, or unobtainium 4 rotor, is almost impossible, they have mostly blown up ,and destroyed beyond repair.

and finally,the money it would cost? YES i'll stick to my plan for an AUDI V12 Diesel , 750HP, and 1000lb.ft. at 4500RPM, torque comin in below 1500rpm!

engine weight just about even with the overweight JAG V12s.

i can just imagine at a car show ,lifting the hood and people seein a big Diesel! makes it all worth the effort, like Cadjag says " different strokes for different folks"

Ron

 

As said, the weight info was from a friend. I have yet to lift a 13B. But it would still be a really interesting conversion.