Powerhouse Jaguar XJR / XJ8 4.0 V8 Supercharger Lower Pulley Performance 18% (X308)

Regular price £236.00


18.6% performance upgrade lower supercharger drive pulley with special length drive belt for Jaguar XJR / XJ8 4.0 V8 (X308) 1998 - 2002.

The pulley replaces the existing outer drive section of your crankshaft damper unit which will require modification to install.

These pulleys are CNC machined from high grade billet aluminium. Produced to the highest dimensional tolerances and surface finish to that of any on the market.

Supercharger pulleys are the most proven and best £/Bhp performance enhancement available for supercharged engines. Changing the pulley ratio results in the supercharger working at a higher speed and producing more boost. Because this just directly increases airflow through the car’s existing sensors, the ECU is kept aware of the increased flow and no further alterations or remapping are necessary.


Boost & Power gains:

On 4.0 engines, the lower pulley mod yields much better results than the upper pulley. This modification gives an 18.6% supercharger driven speed increase, which equates to about a 3.5psi boost pressure rise. It will make the car feel as though the engine has grown by a litre. These upgrades have been fitted to many cars, result vary but discussion on forums and bar stools confirm about a 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 increase tailing off towards redline where engines are least used, this modification gives a HUGE increase in instant grunt and acceleration which really does transform the car. 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.


Sale Includes:

  • 1 x Uprated Alloy Performance Crank Pulley 18.6%
  • 4 x Stainless Steel Torx Mounting Bolts
  • Special length Supercharger belt to suit
  • Installation/Modification Instructions



Before purchasing first check that you have the correct damper that can be modified. Some models of the 4.0 used a different damper that cannot be modified to use this pulley. Please refer to our images to find which is the correct version. To help, the pulleys we can modify have solid outer pulleys, the incorrect version can be identified by the presence of a rubber band between the pulley and the hub.

In order to install this pulley you will need access to a lathe large enough to work on the damper. We provide instructions with pictorial guides for this process. In brief it requires the existing pulley to be machined off and down to a hub size that the new pulley can sit on. Then some drilling and tapping to secure the pulley in place and it's done. If you don't have access to or do not have the required lathe skills we also offer a few services to suite you. You can simply send us your damper and we will modify and install the pulley for £209. Or if you wish to save a little time we can offer exchange however we do charge a £250 returnable deposit until your damper has arrived. If you have a little more time you can send in your damper and we will ship a stocked item same day we receive. No deposit is required for this. Please bare in mind that any returned damper must be in good useable condition, broken extractor threads, bent pulleys or excessive damage will affect the return deposit amount or the ability to supply a replacement.

If you already have an upper performance pulley, the combination of the two will generate a lot of excess heat both affecting performance and reliability. We advise upgrading the intercooler and chargecooler electric pump to minimise the temperature increase.


Part Number




Jaguar XJR / XJ8 4.0 V8 (X308) 1998 - 2002.