PPF= Power plant frame.
Unlike a normal car a miata doesnt have a tranny mount, the tranny is mounted to the Diff buy a Frame, Called the PPF.
http://i61.photobucket.com/albums/h8...a/P8100156.jpg
Google Image Result for http://www.angelfire.com/ca2/92redmiata/images/frameT.gif
You can look at my car in person some time if you want