The rotor sucks air in from the center of the rotor, pumps it through the vanes, and out through the outside edge of the rotor. This “centrifugal pump” design helps the rotor dissipate heat. If you install a curved vane rotor backwards, it won't be able to pump air as effectively
"As with the plain rotors discussed above, the internal vanes should lean toward the back of the car. "The direction of the slots on the outside of the rotor do not dictate whether the rotor is a left or a right." For rotors with slots machined in the same direction as the internal cooling vanes, the slots should lean toward the back of the car. For rotors with slots machined in the opposite direction as the internal cooling vanes, the slots should lean toward the front of the car. Bottom line - don't use the slots to decide which side to mount the rotor. Pay attention to the internal cooling vanes."