Im probably going to get thrown out of this forum but im looking for people who have done a ls engine swap in there XJS. I love the classy lines of the car and love the hp and ease of the Chevy ls engines. I think its the perfect combo of two great nations. I would like toask some questions on the topic. Sorry hard core jag fans.

 

Not me but this was on Craigslist a while ago.
https://rochester.craigslist.org/cto...016211703.html

 

Ask away... Not getting thrown out. Lots of converts here. but here's some info for you.

What years XJS? Auto or Manual?

Very early or Late (post 93+) are the best to convert becasue of rear end gears.

You drop so much weight from a V12 car that you will need to lower or replace the front springs.

Any thing more than an LS1 (360HP) will require many other upgrade if you want control and the ability to use that power. As you approach 400HP the rear cage control become an issue IF you have the traction modern tires can offer.

It's economical to have a doner car, lots of LS1 / LS2 GTO's around for sale to use for a great price.

Do you weld / fabricate? If so make your own mounts so you can push the engine far back in the chassis for amazing handling, if not then you'll have to buy pre-made motor mount adapter setup.

 

I was thinking one of the newer models and convertible. I was reading the Jag kits available and they make it sound so easy but im sure its not. You would think that because they had a 6.0L v12 that it could handle some hp. I was thinking of a LQ4 400 whp. Will I have to change anything major with the suspension? I dont weld or fabricate but I have friends and I didnt rebuild engines either but i did one. Always willing to learn. Should I conciser the xj8?

 

I meant XK8

 

What are you building? A cruiser? I assume it's just a quick cruiser because old converts dont lend themselves to high performance levels.

How do you plan on getting an LQ4 to 400 HP?. It's a low compression truck motor with a very small cam. 340 would be easier with cam upgrade if you've got the 317 heads... that's a great power level for a "bolt on"s" XJS.

Late converts have front and rear X braces which helps much. With 400 HP....IF you have traction the rear cage will want to rotate up and cause wheel hop and make quick work of the bushings. Many, including myself have successfully managed this issue with by bracing.the lower cage.to the body with a strut rod or 2.

I have a 1994 XJS V12 convert. It's in a good state of tune and handles it's 300 HP just fine in most situations. You can tell it's a-bit stressed though, V12 converts are heavy, cruisers, and dont like to be pushed too hard. They get jiggly with a V12 but that might improve with a lighter LS engine. . Once you go down the performance spiral with any car you need better wheels, tires, performance shocks, brakes, springs etc. Everyone starts with the engine but it's really just once piece of the puzzle so plan accordingly.

I also have, in my possession, the only 6 speed v12 6.0L I know of in the USA and it's got all the upgrades. ... shocks, sway bars, EBC pads, it's lowered, rebushed, 17' wheels with UHP tires and some chassis bracing. On occasion I drive both XJS's back to back... I cant believe it's basically the same car.

XK8 is a diffrent platform I know little about but generally speaking converting later cars can be a bit more involved with all the electronic interfaces and possible emmisions regualtions with 1996+ cars. Still doable but the price starts to get irrational fast considering there are many many high performance cars that can be bought in the 5 to 10k range these days. Possible many more soon as electrics become all the rage. For example I just bought a LS2 2005 GTO with a six speed. I couldn't buy the engine and trans alone on EBAY for what I paid for the whole car. Tidy except for some ripped seats, missing shifter boot and dodgy power windows, All easily sorted or unimportant for me becasue it's becoming a track car. Point is...unless you are building something unique or very specific it can be economically irrational but many things are so do what makes you want to jump in the seat again and again.

 

Hello jpeery

This is my opinion only - but I totally agree regarding "what is your plan?" It really needs to be defined before you start - other wise you will get what I call scope creep which equals budget blow out.

Also - have you considered purchasing a vehicle that has already been converted - here in Oz, there seems to be quite a few that are on the market just lately, of course you then fall into trap of is it a good convert or not,
On this forum, there are stories of successful and unsuccessful converts.

What ever you choose, the advice is here, and you are right, the lines of the XJS is what attracted me when I entered my mid life crisis

Cheers
Steve .

 

This seems like a good deal. It's a "late late" XJs with the better brakes. Seats are a bit worm but looks like a well done conversion. If this is what someone wants...it's a buy becasue it would be hard to duplicate it for that price. Lots of Bolt on's to get that LT1 performance up if desired.

This is why I make my own mounts... there's lots of room to set the engine back and as it goes back it can also go lower as oil pan clearance imporves. This allows for a better center of gravity if that's important to you. I can tell you that an XJ with an SBC set back and low handles great.

 

Sorta like the LT1 in my 83 XJ6. Iron engine. Donor was a 94 Cadillac Fleetwood Brougham.
The tune is a great fit to my heavy Jaguar. Torque at relatively low RPM. .

Not a Hot Rod. Sounds great, drives great. Easy 70 in OD but, with punch not needing a shift down..

The frot mounts on my engine have two posssible bolt combinations. The Johnscars kt mounts use the front ones. Engine is set back in that manner.

Done in a long stretch. began 2001 Got final smog OK in 2006.

Carl

 

The lq4 engine is the perfect block to start with.new cam ls6 heads with the truck manifold(if it fits under the hood) proper tune and supporting parts, I think i can achieve near that level of hp. Im now wondering if I should use a jag now. I kind of figured since it had a v12 i didnt have to beef up anything. With the engine and electrical issues that they had, i thought i could solve all that and have a fast convertible. Cant believe that the frame and chassis cant handle another 100 hp.

 

What did you mean by ,What is your plan?, I said i was looking at maybe a 90s XJS with a ls engine at around 400 hp. Jag specialties sells a pretty good kit for around $900,and they say no welding or fab work. Anyone use them?

 

What did you mean by ,What is your plan?, I said i was looking at maybe a 90s XJS with a ls engine at around 400 hp. Jag specialties sells a pretty good kit for around $900,and they say no welding or fab work. Anyone use them? BTW a 6.0L truck engine starts with 300 hp ,stock.

 

XKR Convertible can handle 400HP. They already have nearly that from the factory. It's a newer design and you can buy a lower mileage one for less than the price of building you own 400HP XJS and it'll be a better car in the end. The XK's have a few KEY changes made to the rear suspension that are critical for performance but they're not the sedate cruiser that the XJS is.

Lot's of people make that assumption and think the V12 is some sort if power house... It's more smooth and refined than anything else. In every OE configuration the 3 or 4 speed trans really puts a lid on the V12's power delivery. Like I said before at 400 HP you'll need lots of upgrade to the rear suspension and wheels, tires and brakes to control it. Plan and budget accordingly. It' can be lots of fun though.

Which LQ4?. The alu headed LQ4 has good heads, the early LQ4 has a puny cam and iron heads. If it's the 317 Alu headed LQ4, I'd run that just like it is or pehaps with just a Z06 cam, that will approach your crank HP goals It's really gonna cost alot of money to get the early LQ4 to 400HP ($4000) and that power you really cant use on an XJS unless you have many other upgrades. At this point even the last and best XJS is still 25 years old so all the bushes, springs, shocks, etc will need doing in any case,

Over the summer I drove a 1994 convert with a 2015 5.3 from a silverado. (355 HP) It was fine but at the limit, On a warm day on sticky pavement it had a lot of wheel hop and got squirly out back under power. It was brought to me to fix some of these issues. It was a great drive and nice as long as you didnt push it .. those square port headed 5.3 really likes to rev so it was great fun winding it out... and the 6 speed auto shifts real quick and smooth. Most refined convert I ever drove at modest speeds. Once pushed it was clear everything needed upgrading. Bushes, springs, shocks etc... All great fun and rewarding i you like doing that stuff as many here do.

I was asking about the plan...as in how do you plan to use it? If it's just a cruiser...any LS will do... 340+ HP with good fuel economy in a covert will be tons of fun and wont break the bank.

 

yes. Andrew at Jaguar Specialties is the real deal

 

Thank you for the advice.I think im going to go the XK8 route and maybe a 6 speed standard shift for fun.

 

so much for that!

 

perhaps an early xk8 the later ones are a PIA. You cant even change a bulb without it throwing a fit. I got rid of mine and bought an older XJS>

 

Consider a Late 6.0 XJS with a 6 speed manual. That would be unique... I have in my possession what I think is the only one in the USA. There is NOTHING else like it. I have a few 1 of 1 cars and 4 have 6 speeds but the XJS is by far my favorite. It's not the fastest car I have but there's something special about row'in a T56 Magnum behind a V12. I can't put it in to words, it just something you have to experience.

 

jperry223-

I would be happy to fill you in on the details of any of these cars with an LS- 6speed manual. Agree to disagree, but there is really nothing like the tractable, reliable, smooth, and seamless power of an LS engine, particularly in a Jag chassis. If an XJS is your bag, the absolute icing on the cake is that an aluminum LS drivetrain gives you almost perfect weight distribution vs the nose heavy V12 option (as well as a 350+ lb weight loss over the V12 automatic cars based on an actual car on an actual scale). And in an XK8, the car with an LS/manual trans is simply transformed, making it really the sporting car Jaguar should have built.

Conversions on these models are not difficult with the proper parts. The finished experience is well worth the effort, and that is coming from someone who has touched/driven all of the different variants at one time or another, V12 or otherwise. Not many out there can offer an opinion from that vantage point.

Friendly advice- in the area of conversions on these great cars, by all means talk to everyone and anyone you can about the options. But be sure to be aware that pointed/negative opinions sometimes come out of a lack of firsthand knowledge rather than in-person, in the seat experiences.

For more info, get in touch with me offline at your convenience

Thanks
Andrew
Jaguar Specialties

 

No doubt an LS with a 6 speed in any car is special but kind of common these days... I have one of those too in the form of a GTO... It's great too... BUT... A 6.0L V12 with a 6 speed now that's something really special. Like nothing else, except... perhaps a Ferrari, Lamborghini and the like.... I don't think Andrew ever drove an 6.0 XJS with T56 Magnum... becasue I have one of the few that exist on the planet. Andrew correct me if I'm wrong and perhaps share a video... As for the special-ness...I'm being very specific...the 6.0... not the 5.3. The 6.0 is in another league as far as refinement and durability and when paired with a T56 Magnum it comes alive and offers a fantastic drive.

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