Hey guys,
 
Does anyone know if the Gen 3 NA headers are welded to the flange on the inside of the primary tubes? I know some manufacturers do this (MX5s have this for example) and the result is a big weld bead on the inside of each primary header tube right at the start where the exhaust is leaving the head. This effectively brings the tube diameter down something like 6-10mm depending on weld size, at the point where flow should be maximised. If someone has one laying around and could check for me that would save me having to rip my one out to have a look.
 
If it is welded internally I'd like to pull the header off and grind out the welds to make nice smooth tubes. I think there should be at least a small gain here since the very start of the exhaust system is where smooth flow would be most important.
 
Cheers,
Adrian

I am familiar with the Gen 2 stock headers and the primary pipes are welded only on the outside of the mounting flange leaving the pipe inside smooth. Obviously the best way to do it
I know the Gen 3 head ports are different but the headers look much the same design.
You could check for sure by removing your top heat shield to allow you to see the weld.
 

Another thing I have noticed on the Gen 2 headers is that the pipe diameter is noticeably larger than the head ports, perhaps designed that way to prevent exhaust gas reversion.
If  the MX5 is the same, even if there was a protruding weld inside the flange it may not interfere with the flow anyway.

Thanks mate. Appreciate the advice. The MX5 header is welded both internally and externally. So the Gen 3 may be the same. Might have to take it off to get a proper look.