I have cut / pasted a few sites from my booklist which may help.
NACA evolved into NASA and RACE Magazine is a local (Australian) car tech mag. They ran a series of article on aero wings and profiles and how to build them.
naca.larc.nasa.gov.
http://www.hanleyinnovations.com/racecar1.html
Race Magazine - Home
Look specifically for wings / section with the numbers E 423 (E is for Eppler) and NACA
4415.
The NACA numbers mean:
First number: amount of camber of the mean line
Second number: Where it occurs
Last two numbers: Thickness to chord ratio.
So for 4415: 4 degrees , 40 % back from the leading edge ; with 15% t/c.
Hope this helps,
Pete.