Facinating information guys, thank you.I have a 5.3l 1988 Xjs called thunder. Alu flywheel and match to a 4 speed manual xj gearbox. Im seriously considering boosing her for power as the cost of getting power out of her in NA form seems extreme relative to the returns.
the 2.0 subari pistons sound like the way to go....I have engines and access to my own workshop, but i would appreciate any assistance with information to avoid costly trial and error r&d....Help

 

The reason so many people have trouble making the EFI work with aftermarket systems is two fold.
1st
Few actually know that much about fuel injection, while they can discuss things knowledgeably they’ve never actually worked on it ( including a fair number of mechanics paid to work on our cars) and that lack of knowledge combined with wrong information on sites like this scares and confuses them. They want simple plug and play solutions. They think putting carbs on is that plug and play sort of solution.
Carbs do not work well with turbo chargers.

2nd
Unlike most modern cars, most systems on Jaguar V12’s are not digital. They are analog. Including, especially including the sensors. Adapting sensors or getting the ECM to speak analog is really difficult.

3rd. Even systems with self learning capabilities ( Mega Squirt) cannot achieve perfection without input from your laptop while you drive. While it is possible to adapt the later distributor less ignition system to fully develop the potential of the V12, there would be thousands of man hours expended to achieve what the factory did. Plus you would have a car unique to others. Not necessarily better. Plus one without shop manuals to guide future owners how to tune or fix.
The factory took 21 years to develop the fuel injection system for our XJS using the most advanced technology available. Yet even the newest is more than 25 years out of date and took ideas out of Ford’s parts bin that had already been superseded. It is at least 6 generations outdated.

While it can be done for racing, racing is far less complex than street driving. Especially when fuel mileage or pollution levels isn’t a factor.

 

Ferrari, Aston Martin, etc etc etc all went to side intake. It’s easier to get equal length in the plenum with side than front. Plus the V12 is long, add a intake to the front of it?

 

turbo’s in the engine compartment bring serious heat issues with them. The added heat in an already crowded compartment is a sure way to cause valve springs to fail. ( even if you can find a way to keep gaskets from leaking)
So don’t put the turbo’s there. Tuck them under the front fenders behind the tire. One on each side. I know T2’s fit. I’ll have to check on T3’s.
with regard wider tires. Back in the 1980’s JaguarXJS in Group A touring car used 17x10 inch rims without changing the fender line. It also allowed 14 inch brake rotors.