The GTT S/C pulley is featured in all GTT conversions (except GTT190) , and is responsible for supplying the additional boost, that provides much of the power increase in all Cooper S performance conversions (JCW included ! ).
GTT use high quality carbon steel, this has many advantages over aluminium /duralium etc. Even though it is more costly to manufacture due to the slower machining feed rates. Firstly the Superchargers drive shaft is produced in steel therefore only steel pulleys will expand at the same rate ensuring the grip on the shaft is maintained at high temps and rpm.
Also steel is considerably harder wearing than duralium /aluminium etc, ensuring our pulleys last the distance. Small amounts of wear on the pulley will greatly increase the risk of power robbing belt slip, remember the S/C requires considerable force to turn it! The OE pulley is manufactured from steel and finished in black paint. The GTT item is also finished in black epoxy with the added benefit that its discrete ‘similar to OE’ appearance does not draw the unwanted attention that a bright silver pulley will, or even worse one with a ring of bolts around it!.
The original pulley is an interference fit on the shaft. GTT too has adopted this method. This has considerably less risk of coming loose than the tapered bore types which rely on a ring of small bolts to supply clamping pressure to a collet. One area worth mentioning is the removal of the OE pulley.
GTT use their own purpose designed tooling to remove it with no risk whatsoever of supercharger damage. Even the OE pulley itself comes off 100% intact. The GTT pulley uses a clever remove/refit system making it relatively easy to return to standard should you ever wish to. We return the original pulley to the customer after each conversion.
A Must Read Article!: http://www.gtt.uk.com/bolt-on-vs-interference-fit-supercharger-pulleys/
Fits: Gen 1 Cooper S (also JCW / GP1)