How to install a supercharger on a xjs v12 5.3?

Answer 1

It's not possible to give a one line answer here, and one needs to read up on the subject in great depth to understand the issues. For example, with more power there will be more heat produced by the engine and this needs to be dissipated - larger radiator, bigger fan - that sort of thing. There are two main types of supercharger - centrifugal and screw - each with significant pros and cons. Centrifugal are small (looking a little like a turbocharger) so relatively easy to fit in the cramped XJS engine bay but only produce useful pressure at high speeds so boost takes a while to kick in - not what you expect from a V12. Screw-type compressors are more efficient and have a wider range of boost speed - but are more difficult to fit (especially on the V12) and are more expensive.

Then you need to consider charge cooling. The compressor will make the air/fuel into the engine hot - not what you want for efficiency, so an intercooler needs to be designed and fitted - a big challenge in the XJS! There is a choice of air to air or water to air cooling.

Then there's the engine structure. Will it take the additional combustion pressures? Any latent defect (cracked conrod etc) will be provoked by an increase in power. So the engine needs at least to be blue-printed and preferably have a stronger crankshaft and beefed-up conrods. The HE V12 is less suitable for supercharging as the lean-burn head limits A/F ingress, so really one needs to change to the earlier flat-head engine. You need to consider the compression ratio - the HE at 12:1 will be too high.

The engine computer (ECU) will need to be re-mapped for supercharger use as the amount of fuel used will be very different - and the ignition timing will need to be modified. The Lucas ECU can't be re-mapped in the modern sense, so a new engine management system will need to be designed and installed - a fairly major task in itself.

So - it's all do-able, but nothing you'll need is off the shelf, there are no kits, so it has to be a one-off design. There are some private individuals who have done this, and Lister made the Lister Le Mans supercharged 7 litre XJS. I'd strongly recommend finding one of these rather than attempting to do it yourself on your own car. But if you do go ahead, be prepared for a spend of at least £20,000 - even with you doing some of the work yourself.

Having said all of that, I do encourage people to have a go, so if you approach it with a well-filled wallet, lots of time and patience and the utter preparedness for failure it can all be fun!