i have a hytech rep. header n can keep ac/ps but its on an eg chassis. ive heard good things abot megan headers. but ur gonna get the most power out of a header with a 2.5" collector. generally all headers bolt up to the cat and keep the factory 02 housing. however if u get one with a 2.5" collector be prepared to buy a jdm type r cat or some sort of test pipe to bolt up to it. yout stock cat wont work.