Enable Verbose Boot

For the Repair Volume:

Mount the repair partition.

mkdir /mnt/repair/
mount -t hfs /dev/disk0s2 /mnt/repair/
then edit /mnt/repair/com.apple.Boot.plist

Under key: Kernel Flags

add -v before rp=:///OS.dmg

For the normal OSBoot Volume:

edit /System/Library/CoreServices/com.apple.Boot.plist

Under key: Kernel Flags

add -v

Thanks to phoem for this information.