Hello all! I am new here and have always loved the XJS' lines. I would like to know what people have done to "hot rod" their XJS.... I am considering something street legal, lowered, sharpen up the steering and build a canyon carver out of an XJS.

I don't have one...yet, but want to know if people have done this..... And what they have done. I did a search and little came up. That may be a sign!

John

 

Here is lower, and sharper.

The limit is your wallet and skill, guys have made 9 liter engines out of the V12, race car replicas that would give any modern car a beating, twin superchargers. One shop in Portland took a XJ6 sedan and turbo charged it with cantilever suspension going on to win drift race competitions cranking out 400hp/420torque on an otherwise stock car.

I replaced all my suspension with racing-spec polyurethane and with the 30+ bushings and bits that is alot of play you can eliminate making it handle very very sharply with uprated shocks, you can go further with ultra stiff springs to.

Squeezing power out of the car is a matter of small cumulative upgrades - and this is where you can spend tens of thousands. I deleted all mufflers, added high flow intake etc it makes for a noticable difference but your better off going manual trans or a more-than-3-speed gear box as the car (with 3spd auto) isn't the best configuration for power...or fuel mpg.

Here is a V12 coupe (same basics same engine as XJS) with alot of mods youll notice its stiff and breaths deep.

 

There are lots of 'hotrodded' XJS' out there. The haters seem to dominate though. How far do you want to go? Hot rodding an XJ or XJS isnt a bolt-on affair. Its more traditional in the sense that you need to make or re-purpose many things to fit and work right. Doing so well, quickly and on the cheap is a American thing popularized by Adrenalin junkie GI's who returned home after WW2 with the skills but little resources. The Australians seem to have ran with it too!

There's a series on amazon with Kevin Tetz. Well done, uses a LS and 4L80e. Its a great trans but a bit heavy, lazy and slushy and just not ideal for performance hotrod. XJS isnt a truck... It needs a more dynamic trans like a well built 4l60e or proper T56.
There's lots on FB. Many a project get started but doesnt finish. Often these projects get off to a brisk start and stall. It's a good idea to keep the spend and performance expectations reasonable, in most cases you wont be able to out run or out handle a new Honda Civic sport unless you spend what a new honda civic sport cost or have some serious performance car building cred. Ideal to start with a running donor car so you have most of the little stuff you'll need.

Sticking with V12,
The only upgrade that is worth doing is 5 or 6 speed conversion with a diff change. No meaningful HP upgrades possible for the V12 unless you spend mega bucks and mega time and thats not what hotrodding is all about. It's been a long time since anyone has proven and published any HP increases for the V12 as a DIY endeavor.

Converting to a V8
90's Chevy LT1 is a good match and costs are reasonable. If done right with alu heads...It drops at least 400Lbs off the nose and with typical mods like headers and roller rockers its at the limit of what the chassis can handle so only basic chassis upgrades are necessary. The weight drop helps everything, especially handling and breaking. Any LS conversion other than a 4.8 will overwhelm the chassis IF you have traction. No traction...no problem. If you want to get the power to the ground you'll need to brace the IRS. In the pict below you can see a propper V8 exhaust and IRS bracing.

Handling...
Addco makes a front sway bar, available on Summit, Small rear bar from early XJS works well in conjunction. Sticky UHP tires and Lowering helps handling a lot. You can lower the car with Aftermarket springs, or front pan spacers and rear spaced and welded lower shock collars. Bilstein and /or KYB shocks are fine for anything but technical tracks or drifting. I've done it all, track tested too, look up my posts. These cars a a lot of fun to hotrod. If done properly you can retain lots of the refinement, increase handling dramatically and the ride doesn't get unreasonably harsh.

Braking
Adding rear outboard brakes for a later XJS or XJ40 offers up a big improvement, EBC Red pads are good for the Street on stock brakes and good rotors. That's the only bolts on out there. Bigger requires fabrication or using late DB7 stuff that is hard to find. I'm working using XJ300 front spindles on an XJS with bigger rotors and pads but also needs a fabricated front upper control arm to keep the geometry right.


Proper exhaust, IRS, Front and rear X and ladder bracing shown.

 

Thank you, gentlemen! That's what I was looking for! Something fun to drive around and tinker on. I will look at FB and the other links and ideas that were posted!

 

The suspension and steering are surprisingly good stock. You might want to drive one before you think about suspension mods. The stock exhaust system is restrictive and quiet. The intake airboxes can be easily modified for more power and more sound. The stock transmission is abysmally awful. It can be re-tuned for some improvement. I'm saving up for a five speed swap. The 2.88 diff is a bit tall as well. Some people have swapped to 3.54 or 3.73s along with overdrive transmission and generally seem to be happy with them.

There are big bore throttle kits, ECU retuning, exhaust systems, and other go fast goodies available from companies like Simply Performance and AJ6 Engineering.

The car is also criminally heavy. The book says curb weight on mine was 4040 pounds new. I weighed it not long ago and found it about 180 pounds lighter than that with a couple of mufflers and some of the interior deleted. There's a guy on here who says he's gotten them down to 2700 pounds, but it's not a quick or fun process. Remember, if you add power, it makes you faster in the straights. If you subtract weight, it makes you faster everywhere.

 

Power to weight ratio, is the key. Everything is a balance. The better the balance, the faster you will go. Now all you have to figure out is how. LOL!

Jack

 

Just some tech comments regarding the XJS and conversions- these are fabulous cars with a modest V8 under the hood. What isn't always so obvious is that the process of converting to the GM engine trims a large amount of weight off the car, mostly from the front end (~ 300 lbs for most small block Chevy and LT1 engines to as much as 400lbs for the LS engines). The cars handle and drive very differently, now being evenly balanced (I've had several of them on the scales over the years and they come in very very near 50-50 weight distribution a major plus everyone can agree on. And that weight savings makes even moderate output replacement engines in these cars seem like much more than that middle 300's- 400 hp range they are. We have more than a few customers running the 6.0L LS2 engines in their XJS' and find the cars do everything pretty well. My own 88 XJSC with (a mere) 325hp LS1, 6 speed manual, and 3.54 diff is quick, linear, perfectly predictable on acceleration and in the turns- no surprises.

By all means look into further, ask questions, drive them all (and if possible try out a converted car in person). Then you can have a good understanding of what's involved.

I hope that helps

Andrew
Jaguar Specialties

 

To those advocating Small block or even big block Chevies.
Stock they start out up to 102 horsepower less or even greater loss if you wind up with a 305.

Weight wise You start out with a V12 that weighs 730 with 16 pounds of cast iron exhaust manifolds. That is minus A/C alternator air pump and power steering pump. But with starter. You can lose some weight by going to a gear reduction starter.

Chevy Small block with similar equipment is not 300 pounds closer to 450 pounds. Unless aluminum heads are purchased, aluminum intake, aluminum water pump, etc. are added with the increased cost they represent.

The big block weighs 680 pounds in similar configuration. Again you can reduce that weight by buying ( at extra expense) Aluminum heads, intake, water pump.
Power wise the 454 put out 230 horsepower. SAE net. Compared to 262 DIN net 299 Euro spec. 314 for the 6.0 ( multiply times 1.00139 for SAE numbers).

Yes a newer LS starts out at 330 SAE net and can be 100 pounds lighter.
But about the same time Jaguar stopped
making the V12 and started making their own V8
and that V8 stock can have up to 560 horsepower.

I do happen to absolutely agree that a manual gear box transforms a XJS. The 5 or 6 speed manual From a Chevy can either be installed in any XJS with a GM Turbo 400 transmission or later using a kit or just making your own adaptor plate from a plate of aluminum. A mornings work with a drill press and a band saw.

 

this has been around close to 26yrs now!
it is a great Hotrod car , many mods, custom built V12 , 700R4 overdrive trans, 3.73 rear gears, with Positraction!
weighs 3450 lbs, lot of suspension mods!
it is a great STREET driver , and pretty good MPG!

side pipes

355 Wheel HP, 400 at flywheel!

single piece ALUMINUM drive shaft

 

Thank you Andrew. I have also looked at Miatas...... They don't do much for me save being a good place to learn more about cars.

This XJS community seems to be more my speed of tinkering. Having been an aircraft mechanic and comfortable doing some work on my Volvo V70R, with help from the forums and youtube, I would like to wade into something that doesn't have to be put back together by Monday morning for the drive to work!

 

Thanks Mguar,
I do like the idea of the V-12...... As I said I have looked at MIatas as a place to start tinkering on cars and move on to an XJS....An LS in a Miata is a $10K+ effort.

 

Thanks! Thats kinda what I had in mind. Not joining the throngs of Miatas, 911s etc. Something rare! Something....mine!

 

mine is probably what some might consider a hot rod jaguar its got a roots blown small block Chevy in it making around 600hp currently. 700r4 trans 3.54 gears 245/40/18 front tires 265/35/18 in the rear chassis is currently mostly stock, other than ebc brakes, going to be adding a rear sway bar and bigger front sway bar hopefully next week. drive it quite a bit auto cross it. haven't had it on a drag strip yet as i don't really want to put a roll bar in it and nhra rules won't let me run faster than a 13.50 without a roll bar and the car should be able to run deep in the 11's mostly its just a fun overpowered street car.

 

As offensive as ezrider's car is to Jaguar purests I have to say the image of a full on burnout with that huge hood supercharger thing is quite good. Did you ever redo the suspension and ditch the sloppy spongey OEM rubber bushings?

Side note: rear swaybar actually causes more tire lift off and badly effects cornering. Theres an interview with one of the original engineers who said as much, they only had them because the order was already placed.

 

I don't think it will be a problem as I'm am going larger on the front sway bar at the same time as adding the rear. The car is pretty well balanced stock with the grip level of the stock tires for a luxury GT car. The stock tires feel like around on greased food trays compared to modern performance tires.

With the extra grip of a modern performance tire the car has a crazy amount of body roll witch in turn makes it impossible to maintain a good contact patch with the tire to the road under a heavy cornering load.

I'm still rubber mounted everywhere iv really done very little to the car over the last year other than drive it and change oil and put lots of gas in it...lol well actually e85 have to change the trailing arm bushings every year I do need to do some bracing to the rear cage to get rid of that issue

I just now started working on actually trying to dial in the chassis a bit better for cornering last autocross I got beat by a diesel VW golf by 2 tenths of a second and that is just unacceptable...lol

So far the changes iv made sense then has been to basically give the alignment a tune up. With some negative camber and some toe in. Still pretty mild as I do street drive the car quite a bit but definitely feels a lot better and steering is much more responsive. I moved my 245's from the rear to the front and went to a 265 semi slick in the rear. If my sway bars come in before this weekend I'll get them on before the next event.

I think I am probably pushing my chassis quite a bit harder than most so things might take a bit of experimenting if I do find that I am lifting the rear tire with the sway bars I may need to go to a stiffer spring rate in the front. I am trying to maintain a certain level of comfort street diving the car so I'm hoping the sway bars by themselves will make a substantial difference in getting the car to track flatter under heavy cornering. As the car is now I'm only really using the outer half of my tread width when cornering.

 

Nobody swaps in anemic smog era small/big block Chevy engines into vehicles without doing the simple cheap mods to get the power up to acceptable standards.

And what does the time frame in which the LS hit the streets (1997) have anything to do with it not being an ideal swap into the XJS? The modern Jag v8 is a great engine but not as swap friendly as LS based engines.

If you're simply against "lumping" then say that. There's nothing wrong with being a purist, but don't use incomplete data and subjective reasoning to debate against swapping.

 

I’m not a purist. ( I’m a racer and on a tiny budget) so if I thought a small block was the answer I’d be all in favor. But it’s not.
It’s too expensive. It’s not just the engine you’ll also need the transmission as well because the Jaguar transmission while a GM Has a Jaguar bell housing. you either need an adaptor kit or be able to fabricate your own. Then the whole HVAC will need reworking, plus the instruments( tach especially will be a problem. Driveshaft. And adapt the brake booster, the big one is wiring.

Either you or your mechanic will have to figure all that out. And if it’s the later you have to pay for it.

You mention updating the Chevy in a vain hope to make it as powerful. Building engines isn’t about making it fit, it’s got to be co-ordinated with all the other parts. A more powerful camshaft trades power ( at high revs ) for smoothness at low revs and durability etc. It also needs a bigger carburetor different intake and exhaust etc.

On the rare occasion where the Jaguar V12 has been let down By poor maintenance or neglect and actually fails. A replacement engine is a junkyard away. The sedan and the XJS share the same engine. I’ve never paid very much for them. They’ve always been cheaper than Chevies. Chances are you just need a relatively simple and cheap part to get the fuel injection working again. U Tube explains it all.

Yes the V12 is heavy. It was designed to go out to 8 liters. But it’s all aluminum and even if the block has holes out the sides it can be welded up and reused.

 

Tach is easy you can just use a Dakota digital tach interface. To convert the tach signal

There's a lot more to cam shafts than just moving the rpm range total valve lift and ramp rates play a big part in horsepower gains duration moves the rpm range. Cyl head flow and compression ratio plays a big part as well. When your chasing a big peek hp number your generally adding duration because hp is a function of tq/rpm. But you can biuld a pretty stout engine that doesn't need to spin to the moon to do it but at a certain point your limited by displacement and rpm unless you go forced induction.

Tons of aftermarket support as well as competition between aftermarket suppliers makes it stupid simple and cheap to make power with a Chevy engine of any variety.

A jag power train may be fairly simple and affordable to maintain but when you start talking modifying things the cost difference at 400hp would pay for the entire swap.

The engine in my jag the long block costs me under $1200 to biuld granted I already had the block and the heads. But they could have been bought as cores from a junkyard for $500 all day everyday. Made 400hp before the blower. Probably talking 4-5k in the car running and driving tops if you had to buy every little piece and didn't have any fabrication skills and have some basic mechanical/electrical skills and that's with rebuilding the engine and enough speed parts that will have substantial gains over stock

best engines to use if you don't want to go ls based is the later one pc rear seal factory roller cam blocks. Truck engines made 240-260 stock heads on those engines can support 425hp or so with some minor modifications. The. Corvette lt1s were around 300 stock.

But bottom line is horsepower costs money. Maintaining what the factory made is always the cheapest option

 

Having built my share of Chevy engines over the decades. I know what it takes to build a durable engine for racing. Most Chevy small blocks need a good crank and aftermarket rods.

Jaguar starts with a forged EN 40 steel crankshaft that is hardened. Stock Jaguar rods are good to 600 horsepower.

Flow through Early stock Jaguar heads is capable Of making 450 horsepower. Plus the stock valve springs are solid to 7800 rpm before floating.

Chevy stock valve springs start floating at 5400 rpm. and above 6000 Rpm the stock rocker studs must be replaced with screw in studs. Jaguar doesn't use rocker arms.
Head studs to hold a gasket in place are required under high compression or boost for a Chevy and are stock on Jaguar.

The Zenth Stromberg carburation on Jaguar’s is over 1200 CFM stock and can be upgraded to 4 HD8 SU’s giving 1400 cfm. Yes on a little 326 cu in engine! Stock fuel injection is 1200 CFM and can easily be increased to 1700 CFM.

Making 450 horsepower In a Jaguar V12 requires little more than the correct pistons and camshaft. On the pre HE. Head. At that level the engine is a durable piece with normal maintenance lasting decades of racing.

 

Really not trying to start a pissing match so hope it doesn't come off that way.

What rpm stock valve springs can do doesn't mean anything if you're changing a camshaft your changing the valve springs to match the cam or your going to have a poor preforming engine. Valve springs are a nominal cost.

Late stock cast crank and rods on a sbc are fine for 500hp under 7k rpm. But if you want to go beyond that off the shelf parts are cheaply available and can be had same or next day. As well as pretty much any position configuration.

A good factory Chevy head from the right years can support 400hp with little more than valve springs possibly machining the valve guide to retainer clearance a set of screw in rocker studs is probably $40 on summit.

I would seriously question your claim of what a stock v12 head can support but even assuming that's true I could probably biuld a sbc for what it would cost for 2 custom ground v12 camshafts and 12 custom pistons

Don't get me wrong I'd love to see someone make some serious power out of the v12 I think it would be awesome. But I think Ron bro's is the only one here that has actually made even 400 out of a v12