So….more header talk….this had me scratching my head

Whenever you change headers you ultimately change what's left over in the chamber after a combustion event. It has nothing to do with making the carb richer or leaner as the AFR the carb delivers doesn't change but everything to do with how much residual is left in the chamber to affect the incoming charge and therefore how well the burn proceeds.

Its all about energy imputation and where you use it.