A grain conveyor for a combine harvester capable of increasing capacity and reducing component wear is disclosed. The grain conveyor includes a grain elevator, a transition chamber and an auger assembly. The grain elevator has an inlet for receiving a flow of grain. The transition chamber includes an inlet and an outlet in fluid communication with the transition chamber inlet and the grain elevator inlet. The transition chamber outlet has an asymmetric non-circular opening larger than the non-cylindrical opening of the transition chamber inlet. The auger assembly is operatively connected to the transition chamber and includes an inlet for receiving a flow of grain and an outlet in fluid communication with the transition chamber inlet.