As well as a supercharger the XKR also benefits from a beefier Mercedes Benz W5A580 5 speed automatic transmission, rather than the ZF transmission in the 4.0 XK8 (they were both replaced in the 4.2 cars with a 6 speed ZF transmission). The lack of VVT valves, uprated cooling components and the heavy duty Mercedes gearbox, make the XKR every bit as reliable as the normally aspirated version of the car, whilst being much faster.
The relatively simple Eaton M112 supercharger provides a significant performance improvement over the normally aspirated engine, upping the power from 290 BHP to 375 BHP and dropping the 0-60 time from 6.4s to 5.2s. If you think the XK8 is fast enough for you then you need to try the XKR and feel the shove in the back when you put your foot down along with the howl from the supercharger.
Like the gearbox, the supercharger came from the factory “sealed for life” and officially needs no oil change. Now, 20 years on from its launch, nobody really believes that claim and DIY supercharger oil change kits are available for around £30 so you can change the old sludgy oil with new. The gearbox oil can also be changed as a DIY job, or you can get your local Jaguar specialist to do the work for you. The other service item on the supercharger is the drive belt, which should be changed every 40,000 miles. Superchargers with noisy bearings can be rebuilt by specialist companies for about £270 and its also possible to boost the power output by changing the pulleys for a claimed 10% power increase.
As already discussed, in terms of reliability, the addition of the supercharger does not make the XKR any less reliable than the XK8. The 5 speed Mercedes gearbox is more reliable than the 5 speed ZF used on the XK8 and the lack of VVT components compensate for any additional complexity that comes with the supercharger. All the other weak points of the cars are shared between the two versions and if you are considering buying one now, the supercharger should be low on your list of concerns.