I have read that big cams with lots of overlap allow excess air into the exhaust, resulting in a falsely high reading.
My wideband shows the 451 is idling at 14-14.5 which I doubt is real given the size of the cam: 272 @.050, .652 gross lift, 107 LSA (in at 105), and the smell of the exhaust (not eyewatering or sooty, but definitely not stoich) ;)
