SHELBY GT 350 Member
Joined: Sep 2010
Location: see user name
I've heard .030" max, but Jon probably has a bit more familiarity on the subject than I do. Either way, we both definitely agree that .040" is too much. At that point you are sacrificing too much cylinder wall thickness.
2001 GT Convertible
All the usual bolt-on's /200 I6, C4
And a few Explorers too... 2008 4.0 XLT 4x2, 1996 XLT 5.0 4x2, 2003 Sport Trac XLT 4.0 4x4