One of the challenges with high-boost supercharged engines is belt slip. Harrop offers multiple pulley diameters, but they only have 8-ribs which doesn’t provide enough surface area. Upgrading to a 10-rib belt requires a bunch of changes including a new supercharger pulley. Harrop’s pulley has a large offset and multiple recessed mounting holes, not something you’d want to reverse engineer.
Fortunately ZPE manufacturers pullies for a broad range of superchargers. They offer 8-rib Harrop pullies in nine different diameters ranging from 60 to 85 mm. ZPE was willing to do some non-recurring engineering (NRE) to make me a custom 10-rib pulley with a GripTec Micro finish. GripTec Micro is a patented micro-ablation machining process that creates multi-directional ridges and valleys that increase gripping force and provide escape ducts for trapped air and debris. As can been seen in the picture below, the grooves are micro.
Note that despite increasing the number of ribs by 25%, the mounting screws are still proud of the belt.
I need to pull the engine to install the pulley, so hopefully there aren’t any surprises!