Has anyone tried this? Pros/cons?

 

you'd want to start with an XJR (the supercharged XJ) as your base vehicle. the supercharged engine is stronger than the n/a one and the trans in the XJR is also stronger.

Pros: -cool, you'd be the only person to have one
-would not hurt mpgs as much as the supercharger does

cons: -turbo lag
-not much space in engine compartment for turbo(s) and all the piping you would require
-turbo lag
-tons of custom fabrication of intakes and whatnot
-turbo lag
-people that can tune jaguars are few and far between, even more so for the totally custom tuning required for turbocharging
-turbo lag

 

sticking a turbo under that hood (bonnet) will create a lot of heat in an a compact area loaded with electronics and sensors. not sure if that would be a great idea. you could install the intercooler in the front bumper lower opening, but then you have the trans cooler sitting right behind it. with the amount of money you will spend on the fabrication, installation and calibration, you may as well get a kit from Avos and enjoy a reliable "kick in the pants". i do however agree with XJR02 about the "cool" factor.

 

you could try rear mount turbos I suppose, that would help with under bonnet heat/space problems (maybe) and they tend to sound like a jet engine when they spool up.

 

The only plus point I can think of is the unique 'coolness' factor of having such a machine.

However, from an engineering aspect this is a project fraught with complications all along the way-it would be an immensely big task to complete, as there would be so much time spent 'fine-tuning' the engine management-not to mention ironing out all the installation bugs to make sure the vehicle operates normally under all driving conditions.

It's a 'V' engine so you'll either need 2 turbos, or 1 turbo & suffer the associated imbalance in exhaust flows. There's no 'Y' pipe in the exhaust to ease the use of 1 turbo, so you'd then have to decide which bank to fit a single turbo to. All this assumes you can find the space underbonnet to mount the turbos-along with all the new intake air trunking. It wasn't so bad on the old 6-cylinder Jag engines as it was feasible & there was space there.

But on the V8 you'd be in for a whole heap of issues.

If you have a lot of cash & lot of experience turbocharging engines then you'd stand a better chance-but even professional race engine builders would probably look at the project as a non-starter (no pun intended!) due to the massive alterations required to make it work.

They would just point you in the direction of the XJR & suggest you start with the supercharged car, as it has the stronger transmission & the lower compression pistons needed for forced-induction engines. They would then suggest that you go down the twin-screw route & simply upgrade/improve the standard supercharger installation-that's by far the simplest route to a more powerful X308.

The Devil is always in the detail-so it's not just a case of bolting on a turbo, doing a quick tune-up on the engine management & off you go into the sunset in a cloud of tyre smoke. There will be whole host of issues to deal with, as others have already mentioned here, and you're likely to end up with an unfinished project.

The X308 was never designed to accommodate turbos, but the XJR has the supercharger installation already there-together with a strengthened drivetrain & suspension. All you need to do is improve upon the standard supercharger installation & that would be MUCH easier than going down the turbo route...

From a Thermodynamic point of view, a turbocharged installation is slightly more efficient than a supercharged installation as turbos feed off waste exhaust gas that's already given it's power to the crankshaft-whereas superchargers take their drive power directly from the crankshaft, so you lose out a bit compared to a turbo installation.

But in the real world they'll both be ferocious gas-guzzlers when you drive them hard. Thrash a supercharged XJR & you might get 13mpg-thrash a 'turbo' X308 Jag & you might get 14mpg, so there's not much in it really...

 

First off, with an appropriately sized turbo, say a Borg Warner S400, turbo lag will be minimal to non existant. Even with something as small as a AJ27, you should see full spool by 2000 rpm or less. It'll actually probably be significantly punchier than a supercharger at anything over 1800 rpm or so. Turbo lag isn't a big deal when you have a decent amount of displacement to work with

BUT. This is a bad chassis for a turbo setup. With most custom turbo setups on V engines, you either fabricate a y-pipe that runs both banks forward into a y merge for a single turbo that is placed ahead of the engine; or you run a twin turbo setup with the turbos placed very low behind the engine, down next to the transmission (a lot of GT500 Mustangs run this type). There simply isn't room for option 1 in the XJ without a ton of fabrication work to move the radiator around. You'd also really struggle to find room for an air-to-air front mount intercooler. So the easy option is out. Option 2 also has issues. There isn't much space next to the tranmission in these cars either, making packaging an issue. You're also placing to big heat sources right next to an automatic trans that doesn't appreciate heat too well. And you'd have to either go non-intercooled or run two small intercoolers forward where the brake ducts are now, which lengthens your cold side boost track, increasing lag. There is the third option of a rear mount system, which would actually work pretty well, since there are already big cavities at the back for the rear mufflers that could accept some turbos with minimal mods. And rear mount systems don't really need intercooling due to the long length of tubing that's exposed to flowing air along most of its length. But rear mounts have their own set of issues. This is one car where roots superchargers REALLY just make more sense. The packaging is easy, intercooling is easy because you aren't fighting for space with your boost producer, and the LOW rpm torque hit really suits a heavy car like this well. I have to agree that it'd be neat, but it makes WAY more sense to just grab a twin-screw set up.

Like Red October said though, an XJR6 would be MUCH easier. It's already a plenty strong engine and trans, and being a striaght six, you have all kinds of space to mount the turbo nice and close, and way more space for an intercooler. the only real issue to tackle would be tuning. Hmm. This makes me intigued to try this myself

 

So scrap the turbo charger idea since that sounds like a nightmare - can someone tell me what all parts would be required for adding a supercharger to a xj8? Would the performance outweigh the cost for parts/labor?

 

It would be WAAAY easier to just sell yours and buy an XJR.

 

and MUUUCH cheaper

 

There's already an XJ8 available with a supercharger attached-it's called the XJR

You can't just bolt a supercharger onto a standard XJ8 engine as the compression ratio is too high-that's why the XJR has lower compression pistons. With a high compression ratio & supercharger, you're much more likely to run into detonation & pre-ignition problems due to the extra compression pressures & heat caused by forced induction.

Also, the XJ8 has the ZF 5HP24 transmission which already has it's own share of reliability problems, before you add on the extra power from supercharging-it's also not rated to cope with the higher torque of forced induction engines, so it could fail.

That's why the XJR is fitted with a much stronger Mercedes transmission that's designed to cope with the higher torque from the supercharged engine.

By far the best, cheapest & least troublesome option is to part-exchange your existing XJ8 & go straight for an XJR. With the XJR you've then got a proper baseline to work with-stronger transmission & lower compression pistons. Then you upgrade the supercharger to a twin-screw unit & if you really want mental power, then you fit an uprated differential like a Quaife unit to handle the power.

I also have a Bentley Turbo R with a single-turbo V8 engine. The exhaust plumbing is something to behold in it's own right-with a large pipe coming from the LH exhaust manifold outlet & going under the engine to meet the RH exhaust manifold outlet. They combine both exhaust gas outlets of the V8 into a single input to drive a single big turbo.

It would take a lot of space & fabrication, which you just don't have under the bonnet of the X308. The XJR6 is an easier bet for a turbo installation as you have a narrow single-bank of 6-cylinders with more space to work either side of the engine. I believe that people have successfully added turbos to the 6-cylinder Jags, but I've never heard of it being done to the Jag V8.

It's just too messy, too difficult & not really worth it when you can just go out & buy an XJR with a blower already attached & a stronger drivetrain, suspension & brakes to handle the extra power.

Polish up your existing XJ8 to showroom condition, valet the interior, give it a good service & then just part-ex it for an XJR. It's by far the easiest route to more power & it's also relatively easy to upgrade to the twin-screw supercharger

 

Turbo lag is another term for an improperly designed turbo system.

 

Gosh, that seems like asking for a lot of trouble...for what return?

The twin screw cars are already making more power than they can put to the pavement.

Steve M (the only one who has documented twin screw performance) has proven (actual 1/4 mile run of 12.28 with severely limited traction) that a twin screw equipped XJR is definitely an 11 secondable car, maybe even so on street tires if a limited slip dif is installed.

 

I will add that I wouldn't turbocharge an XJ8 when an XJR engine swap is so damn easy.