I recently installed a 4-1 one piece dc header into my 2000 gsr and I decided to pop out my stock catalytic for better performance. After everything was done my check engine light went on and it read secondary o2 sensor. Will I lose horsepower because of that problem?

 

Try this..Leave ur secondary o2 out of the cat. tie wrap it somewhere. Plug the o2 bung with a bolt. reset your ecu. The check engine light should go away. As fas as performance, I dunno.

 

Are you running a test pipe or did you mean that you're running open headers?

 

why not get the high flow cat?....i dont know about where you are but we have emmissions testing here and they actually check under the car to see if u have one. Mine took some welding and fabricating but we got the O2 sensor in it and have gotten no check engine lights.