Question to all the welders out there!!!

Depending on the quality of header, and the thickness of the flange..

I've lost count,, but dozens of times I've had to Flat file the flange true,, sometimes welding up a low area.. Check the flange sealing surface (welds) with a straight edge..

Other times the flange is warped by over-tightening, particularly the middle two..

This applies to new as well as used headers.

I always check em before I install them..

hope it helps..