I have a DC Sport header on my 98 SH. the top and bottom of each port is 1-2 mm smaller then the port on the head (Total of 2-4 mm too small heightwise). would grinding hte flange of the header to smooth out the flow help the preformamnce in a worth wild way. I know for best results the head and intake should be ported but I do not want to take off the head just to do that. I also have this same issue with my integra header. Can anyone advice on this mod.

 

Before you do that, modify the collector to 2.5"

I'm pretty sure you'd see more improvement.

 

I am running a random tech high flow cat and the inlet and outlets are 2in, I wanted to do this first since i already have a die grinder on hand, my welder is 2600miles away so i cant easily do the collector mod.

 

It always helps smoothing out those ports. Nothing hugely noticeable, but never the less the better the flow, the better the performance. Don't make the holes bigger than the ports on the block however, that would create a lip or divot cause inefficiency