Packet size in SAP 4.7

BW experts,

I need data packages from SAP 4.7 to get 50000 rows at one in a single packet. Right now in BW it is set to get 20000 max per packet. Where can I change it to get more per packet. I am not able to do it on BW side as it say the maximum source system will allow is 20000, where in the source system (SAP 4.7) can I make this change?

Thanks

Ashwin