So after downloading the server pack from FTB website (infinity), I opened up ServerStart.sh and changed
"java -server -Xms512m -Xmx2048M -XX:PermSize=256m -d64 -XX:+UseParNewGC -XX:"
to
"java -server -Xms4G -Xmx4G -XX:PermSize=256m -d64 -XX:+UseParNewGC -XX:"
then made the file...