Thanks. I wanted the USDM's because like 6-7 months ago I read an article in Turbo magazine about headers in their project GS-R. They dyno tested 4 different types of headers: DC Sport 4-2-1, DC Sport 4-1, USDM Type R, and JDM Type R. The USDM's gave the biggest hp increase. Of the ones you just mentioned, is there a particular one that you think is better than the rest?

As for the plugs, I had no idea that that was even an issue when upgrading H/E. I thought the only problem you could run into was that if you went too big, you lose power because your exhaust gases would lose velocity rather than flowing quickly out of your pipe. I didn't talk to my friend for long, but he said that bigger than 2¼ inch would damage them over time (my guess is that if it's true, it's like a slower version of how running nitrous can melt your plugs). I really don't see how another ¼ inch would really hurt, so 2.5 it is

Edit: Alright, I decided on RMF, but I'm having trouble finding someone who sells it. Anyone know a place?