Factory Nissan SR20DET O2 housing are extremely restrictive, ISR Performance Cast 3" O2 Housing are substantially larger allowing the exhaust to flow more efficiently compared to stock ISR Performance Cast O2 Housing is a true 3" O2 housing as Most other O2 housings are 2.7".
** All ISR Performance Products are Designed for Off Road Use Only **
i ordered the cheaper version of this but it was put on intergalactic back order so they swapped me out for this one. wow.......... DO NOT buy the other. this outlet is SO nice. it blows the other out of the water and fits perfect to the isr downpipe.