Never done this before (no header gasket)
Even some of the more costly headers do not have a flat flange.
A flat flange will need no gasket, a hard gasket, or a thin coat of RTV. This is the proper way to get the threads on the mounting bolts to deform in the elastic range where they hold and do not back off.
That said, many big name mass produced headers including TTI and Sanderson put a raised bead on the header. These need a soft gasket to seal. Maybe a heavy RTV would work too, I haven't tried.
I filed and lapped these as best I could but they are what they are.
On my car's current headers, the flanges are flat and just thin coat of orange hi-temp rtv has been effective.
Even some of the more costly headers do not have a flat flange.
A flat flange will need no gasket, a hard gasket, or a thin coat of RTV. This is the proper way to get the threads on the mounting bolts to deform in the elastic range where they hold and do not back off.
That said, many big name mass produced headers including TTI and Sanderson put a raised bead on the header. These need a soft gasket to seal. Maybe a heavy RTV would work too, I haven't tried.
I filed and lapped these as best I could but they are what they are.
On my car's current headers, the flanges are flat and just thin coat of orange hi-temp rtv has been effective.