1 3/4" Primaries, 3" Merge Collectors, 3" X-Pipe (With Cats)Arguably the most amazing hot rod to ever exit a Ford factory, the shelbyby GT500is here. With a mountain of horsepower just waiting to be unleashed, American Racing Headers bolt in long tube header systems can increase power and torque by as much as 40RWHP and 40RWTQ. Like all American Racing Headers systems, construction is all 304 S/S, flanges are 3/8" laser cut and collectors are merge style and incorporate scavenger spikes. X-pipes include 200 cell high flow metallic cats or can be ordered without cats. 1-3/4" primaries come standard. For high boost race applications, special order headers with 1-7/8" primaries are available as well.