Positive displacement supercharger modifications | Supercharger Performance and Engine Performance Parts
Rotor coating
One of the changes between the earlier and later generation Eaton superchargers is that the newer blowers have coated rotors. The rotors are coated with Teflon/Ceramic/Carbide abradeable coating. The coating does two things:
1- Helps the rotors withstand, distribute, and manage heat better especially when using the supercharger at higher rpms.
2- The coating adds thickness to the rotor. When the rotor is heated by its normal operation it expands to a certain extent. If the rotor expands too much within the housing then rather than having a proper seal against the housing wall (to trap air) it may touch the wall causing the whole assembly to catastrophically seize. To prevent this seizure, there is typically a tolerance (a room for error if you will) left between the rotor tip and the housing. This room is bad for performance because it allows the air to escape rather than be trapped by the rotating rotor and thus reduces the superchargers pumping and adiabatic efficiency. To improve efficiency on the later generation superchargers the Eaton engineers have come up with an abrade-able teflon-carbon based coating that makes the rotor slightly thicker. When the rotor expands it now basically touches the housing, but this is now not a metal on metal contact, but rather a metal (housing) to carbon-teflon (rotor coating) contact. What happens here is that the harder material (which is the aluminum housing) wears down the softer material (the carbon-teflon coating) shaping it to the exact shape of the housing and giving a more exact seal between the rotor tip and the housing, better trapping air, improving supercharger flow per rotation, reducing pumping losses, and thus reducing outlet air temperatures. This idea can be used on any twin rotor charger to improve rotor seal and is really a great engineering solution.
