I have a 1998 jaguar XJR with just over 100,000 miles. I have a few mods done to it, such as straight pipe exhaust with an X pipe with stock cats. Upper supercharger, pulley with a supercharger coupler and a Mina gallery cold air intake. I am pretty sure I am close to 400 hp with all the mods that I’ve done to it but I’m planning on making more power more like 500 hp. I’ve done tons of research, trying to figure out a way to make more power. Looks like most people suggest a twinscrew supercharger, but that’s well over my budget and would require possible engine internal upgrade. I could also upgrade my supercharger internals, but with a stock 4 L I’m not sure if it’ll make quite a difference. I am thinking of installing a custom rear mounted turbo to add just an extra 100 hp. I know that sounds kind of stupid but I want to be unique I’m trying to do an LS swap or anything like that. My goal is 500 hp so I don’t need like a big turbo anything.
I’m not sure if the engine would be able to handle the extra 100 hp especially knowing that it’s going to be a twin charge system. Let me know and give me tips and advice on what y’all think. It’ll be a very interesting build I would love to share.

 

Buy a XFR or a LS swap more reliable and more options to increase performance.

 

You're going to want to have a look at your headgaskets before attempting this. I wouldn't do this btw.

 

With the age and mileage of the car I would make sure all the timing stuff has been replaced before modifying anything.
As posted above if performance is your goal consider the costs?
Your 4.0L V-8 is not the best thing to start with and seeing how badly Jaguar's depreciate in price I think the suggestion to look at 5.0L SC cars is a good one!
I have an XJR with the 5.0L SC and it's very easy to modify. It make's 540HP at the wheels and that is VERY conservative!

Also I normally don't recommend an American engine swap BUT your car is in the right year model to do it pretty slick?
Jaguar LS Swap Kit
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There are two of us here on the board doing LS swaps at the moment. PColaPacker is doing an L99 swap into an XJ8 (about 400hp) and I'm doing an LS3 swap into a 2000 XJR. Both of using the Jaguar Specialties kit referenced above. I'm doing some upgrades to my LS motor (bigger cam, etc) and will have about 590hp according to Texas Speed & Performance. Would be cool to have three LS-swap projects going at the same time...

 

Yes your project is where I learned about Jaguar Specialties. They have a really slick swap kit and it looks shockingly factory. Especially the one where they modified the engine cover on the LS engine to read Jaguar!
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I guess it does make sense to do LS swap. I actually had a glimpse at Jaguar specialties conversion pricing it’s not too bad, but where the money will be spent is purchasing a engine and transmission. probably looking at around $10k. And knowing that it’s XJR I would obviously want to put a supercharger 😂 on the LS motor, whichever motor I go with so that’s even more money and cost of getting it tuned and everything. So I will probably do it later on in the future when I have more funds, but at the moment I don’t want to spend more than $6000. Personally, I think if I upgrade my internals on my motor to be able install a rear mount turbo, I think I’ll probably be the first try that it would be a pretty sick build in my opinion compared to LS. But also, let me know what y’all think and how much y’all spent to do your LS swap and how difficult it was.

 

I think 500 crank HP is possible if you ditch the Heaton, fab an adapter for the TB to fit in front of the intercooler (maybe gut them?) tanks, add an adequately sized turbo... somewhere, add a front mount intercooler, maybe a stand alone (??) ECU and of course tuning. Now, to the best of my knowledge I wouldn’t know the limits as far as hp is on these engines. The bottom end might be strong enough but it just might need ARP bolts/studs on the rods, bed plate and definitely on the heads as too much boost lifts them. The head studs aren’t cheap and I have installed a set on a modded XJR-100 as the customer had us install the powerhouse crank pulley and a smaller blower pulley along with a reflashed ECU that we sent over to them. This happened in 2014. I doubt it was 500hp but it sure was fun.

 

@98Jagxjr I think you would be happy with a bigger crank pulley, no felines in the exhaust, limited slip diff, meth and ported blower. Bigger/taller intercooler as well. Anyone still porting our TB's? If so, do that as well.

 

How you approach an LS swap is really about what engine/trans combo you want to use. Plenty of people have done the swap with bone stock, right out of the donor 4.8, 5.3 and 6.0 LS engine/trans and been quite satisfied. Andrew's kits are designed for that approach and I think it works well. I could easily have gone the route of a straight drop in and been perfectly happy. But - I wanted a low mile LS3/6L80E because when I get bored with the LS-powered XJR (and I know I will with a list of past cars to prove this will be no different!) I am planning on keeping the engine for whatever piques my interest next. That said, a typical price point for a 76k mile LS3/6L80E is $9-10k delivered to me in the Austin TX area.

Currently, the fully loaded cost for the LS3 and transmission (before mods and upgrades) is at $4,575. Seriously. How did I do this? Well, I chose to buy a complete donor car (to ensure it was running well, etc) and then part out/sell everything I didn't want or need to reduce the overall outlay. The complete donor car with all CoPart fees, charges, sales tax and delivery was just under $11k all in. I then sold off parts until I had as bare a shell I could stand and then sold that too. Factoring in what I got for each part, shipping costs, etc offset the total cost to the $4,575 referenced above. There is also a bunch of stuff I'll be selling from the XJR once I pull the engine/trans and everything not needed for the swap that will offset the swap kit itself. The XJR it's going into only cost me $1,600. I should be into the entire swap - start to finish - for $10k +/-...

If you have the time, inclination and space to pursue a swap, look into a complete car to get a more powerful LS from the get-go and recoup money by selling off parts, but definitely compare swap costs/options with the recommendations from the others for upgrades to the Jag engine too.

 

Let me just say a few things here if you don't mind though that's your car and you can do anything you like on it.

A 400 hps and 500 hps XJR hps wont make a whole world difference why do you want 500 but not 600 700.. It's an endless chasing game in a black hole...any new EV is stupidly fast as hell.

x308 or any Jaguar is never a cheap platform for anything weekend project...

I and alot of us have/had that thought but a very few got that in the finish line of restomod for reasons.

Money and time ARE your biggest enemy and also it will be a lonely journey that you Will run into a lot of problems once you opened up the Pandora box.. this is not a mustang , not a civic platform.. Not many have done and walked the path before you can share the wisdom with you.

Good luck

 

When you dyno stock 4.0 XJR you see 320-340bhp. That's the baseline.

One important thing almost noone knows confirmed by a Jaf factory engineer
: AJ26SC ECU do not have active knock control above 3,000rpm. This is very
dangerous thing the engine has quite weak cast pistons. Orginal head gaskets are not
good for SC engines. Ignition system is also a baby one and fuel injectors pure 90s design.

Yers ago ( alsmot 10y now ) I destroyd one bottom end partly because of that miseed knock control
and of course a few head gaskets. Another AJ26SC guy lost two engines because of knock . We both had of course 500++hp TS ones. At that time we did know about that ECU secret....

AJ27SC ECU has improved knock control , ECU + sensors, but better ignition system, steel inders from mid 2001 and MLS head gaskets from the same time.

PS. My 12y journey with the car could we valid of 400 pages book 2012 it was just fine 13.5s 1/4 mile and 149mph standing mile car....with Arden ECU, stock SC + big lower pulley, bigger charge cooler radiator + pump, 200cell cats and catback. Very nice car to drive... After that well...a lot faster when it was on the road but tons of problems, tons of time, tons of money ( very many tens of tons actually ) But that's motorsports. Jag motorsports.

 

Good advice from someone who has done it.
One thing missing is the estimated cost of all you did?
Thanks for posting. Learned about the ECU differences too!
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