I am assuming that the powerlog bolts directly to the downpipe which bolts directly to cat? or is this incorrect? Is the ZZP PLOG and Downpipe w ubend delete sufficient for the mods I will be doing or would it still be beneficial to have the headers? How much HP am I passing up on if any if I would use the PLOG/Downpipe vs. the header set up? Can I use the O2s on either setup?