The crankshaft damper pulley fitted to 4.0 Jaguar XJR and XKR models can be upgraded by changing the pulley diameter, increasing the driven speed of the supercharger.

This is a very effective conversion which gives more gain than either of the upper pulley options – the lower pulley provides a 16% overdrive which makes the car feel as though the engine has grown a litre.  When I first fitted this conversion to my own XKR I couldn’t believe it was the same car.  We describe the conversion as adding a litre of capacity to the motor, and are yet to find a customer who disagrees.

Gains

These upgrades have been fitted to many cars.  Results can vary but expect about a 50-60bhp/ftlb gain from this modification.  While this is true for the midrange gain the Eaton M112 supercharger loses efficiency at high rpm so actual peak power gain may realistically be about 10-15bhp.  Irrespective of the gain tailing off towards redline where these engines are least used, this Jaguar supercharger lower pulley modification gives a HUGE increase in instant grunt and acceleration which really does transform the car.

Fitting Both Upper & Lower Pulley

IMPORTANT – if you already have a performance upper pulley, you will need to upgrade your intercooler and intercooler circuit water pump, as inlet air temperatures can rise too high with both pulleys upgraded and risk engine damage unless cooling is addressed.  We have intercooler upgrades available and can advise on required pump.

Before purchasing, first check that you have the correct damper that can be modified.  A small number of later 4.0 cars used a different damper that cannot be modified to use this pulley.  Please refer to our images to see which is the correct version.  The pulleys we can modify have elongated slots and solid outer drive section, the incorrect version can be identified by the presence of a rubber band between the pulley and the hub.

Exchange Pre-Machined Lower Pulley Conversion Kit

Our 4.0 lower pulley upgrades are not sold outright, we sell a service to modify and upgrade your own crank damper unit.  If you ship your 4.0 Jaguar XKR or XJR crank damper pulley to us, we will carry out the necessary machining, assemble the damper and return it to you with a new special length drive belt, ready for you to bolt on.  Cost for this service including parts is £445 plus return shipping.

If you need to remove and refit on your car in a tight timescale, we can send you a completed crank damper unit on exchange basis.  We charge a core exchange fee of £250 which is refundable on receipt of your serviceable old damper.

Outer Drive Pulley & Belt Only

As an alternative to sending us your crank damper unit, or paying a core exchange surcharge, we can send you the parts and instructions to carry out this modification yourself, but it is not something we would recommend as a DIY project unless you have machining experience and access to a workshop with lathe and drill press.  However, if you do have those facilities the machining to convert the damper and fit the upgrade pulley is a relatively straightforward task for an engineering workshop.

We can supply the outer pulley, fasteners and special length belt, along with machining dimensions, for £236 plus shipping, allowing you to carry out the conversion yourself or have your preferred local machine shop do it for you.  This option is an outright sale of the components without any need for you to send your damper to us or pay a core exchange fee.