O2 Sensor H-Pipe Question

[bmxelvs]

I thought of a couple more questions... What should I do next in regaurds to mods? I have been considering a plenum? If I do get a plenum any particular brand? Or a chip of some type just because the speedo is off like 10 percent... Or maybe there is something else that people are doing to the GT's to get good power gains... This is my third 4.6 mustang, however I have been out of the scene for a while. Previoulsy I had a 1996 Cobra and a 2001 Mustang Bullitt both of which were completely stock...