Took the ststem off for a thorough clean & noticed the ends ot the headers that push into the next piece have rolled ends to ease assembly, but these ends reduce/restrict the inside pipe diameter from 37.5 to 32mm. My OCD would not allow me to reassemble like this. Sawn off now. Probly make no difference but hey...
A rolled lip like that will have no positive effect on gas flow unless the ID of the pipe it flows into is very similar.... I’d have still cut it off.
