I have read time and time again about MAC headers causing someone's engine to be destroyed. Theorys are the headers coating is comming off or the welding slag is being sucked up by the EGR. I am by far a modular expert , just a site owner, but I do not recall any of the exhuast gases recirculating through the cylinders. I recall on my 95 GT that the EGR valve opened into a port that ran in the center of the intake, none of the exhuast gases was sucked back into the intake port on the heads. Also if exhuast gas was plumbed back into the intake, wouldn't the intake be smut black inside the runners? I may be wrong but I thought that is how the EGR system ran, and it may well be altogether different on a modular, but I know the modular intakes aren't smut black on the inside either. If that is the case, then how can slag/header coating be sucked back into the cylinders causing engine damage?