I've been driving around with this for over half a year now, I think it does increase high end power, but it's hard to tell for sure because it obviously won't change the curve of the powerband much. Someone on an accord forum had a shop port their runners, dynoed before/after and claimed 7 WHP increase. The 8th gen accord has the K24Z3 which is almost the same as the K24Z7 in the civic SI. Supposedly the V6 accords also dyno gains porting their runners. It does indeed change the sound, it makes the engine slightly deeper and louder.
I heard P2R does not sell this part any more, however I'd recommend just ordering the runners from a honda dealer and working it yourself anyways. The part is called "fuel injector base", it's about $100 so it's much cheaper this way. Then buy some emery cloth/metalsand (basically sandpaper for metal) from home depot and start sanding it out just to smooth the texture. There's no need to enlarge the port too much since it would create a mismatch between the runners and plastic upper manifold. Remember to clean the runners with alcohol when done, ingesting abrasives is obviously horrible for the engine.
Obviously wait until the engine is cold before messing with anything to do with coolant. During install, gently clamping off the coolant line with a needle nose visegrip so you don't lose too much coolant, it is a huge pain to drain and refill.
The fuel system will need to be depressurized, I think the procedure was to open the gas cap, pull the fuel pump fuse and then set the ignition key to "II" without starting.
Use canned air the blow out grains of dirt/sand between the runners and engine, and then again at the injector o ring seals, you don't want dirt falling into the engine. Then put a couple drops of oil into the injector gaskets so the whole assembly pops out easier. The fuel rail doesn't need to be disconnected, it just swings out of the way. I suggest inspecting the injectors, cleaning the o ring seals again, and then bagging it up so it doesn't get dirty when you move it out of the way.
