[Techtalk] creating smaller .iso files with tar ?

[ed orphan]

I've been saving data from my crowed hard drive
by burning CDs.  I do the usual,
mkisofs -r -J -o /my_data/data.iso  /my_data/is_kept_here/
cdrecord -v dev=0,0,0 speed=4 /my_data/data.iso
   I've been disappointed that I can not store close to
700 Megs of my files on the CD. I get about 650 Megs or
so before the .iso file is created. I guess the .iso file
has to contain data for the burning process, or whatever.
   My question is, could I squeeze more data onto
a  700 Meg CD by using tar and gzip first, like:
tar -cvzf  archive.tar.gz /my_data/is_kept_here/
   And then creating the .iso, 
mkisofs -r -J -o /archive.tar.gz  /data.iso  ?