I am currently in the middle of a jdm engine swap. I am not worried emisions, because my state doesnt have emissions checks. I swapped out the jdm spec header in favor of the us spec header because it has a spot for the O2 sensor. How would i go about pluging the hole that connects piping from the header to the intake manifiold? I decided to keep the jdm spec intake manifold on the block. I do not plan to hook up the EGR valve or anything. Is this going to reduce my fuel mileage and decrease my horsepower or increase my fuel mileage and increase my horsepower.

One of 2 ways to block off the useless EGR hole on the header is to cut the pipe at the bolt (plug) and have a shop weld a small metal disc where you just cut it or call Hotshot or Stillen and see if they could send you some header plugs. With the EGR system gone you really won't notice any big change in the car except for cleaner plugs, no throttle stick, no EGR system getting clogged and dumping exhaust gasses in your intake all the bleedin time, no soot buildup in intake, no dogs balls, no BS!!! It's a system that really does nothing but cause problems. You are ahead of the game without it. My emission tests got better when I fixed it, permanently. ;) SMAAAAAASH!

Cossie

Yeah, just take the header to any muffler shop, and they can weld up the holes for you. If you dont ever intend to use the EGR stuff, go ahead and have them completely fill the holes up. When it comes time to get a header, just make sure you order the plugs too, for the holes.