hope this is the right forum. not sure since i have performance internals?
but heres the prob. i just rebuilt my engine it has maybe 75 to 100 miles on it and its throwing a code: 0420 catalyst below threshold bank 1 i belive.
what would cause that ? all connections have been rechecked. i have a .020 overbore head shaved .010 speed pro f/a pistons teflon coated and secret cams with the lo exhaust

a bad cat or a missing cat