A clean install of F17 will have the grub files under /boot/grub2 - grub.cfg being of the most interest (/boot/grub has only the splash.xpm.gz).
To answer the question posed, update the GRUB_CMDLINE_LINUX in the file /etc/default/grub, then run
grub2-mkconfig -o /boot/grub2/grub.cfg
Read the wiki
(noting all caveats), and also take note of my sigline.