here is a good writeup about everything you need to know port and polish related: http://www.sa-motorsports.com/diyport.shtm
and here is my interpretation of it applied to my wrx:
ok so on sunday i had a marathon port and polish in my garage. thanks to wil for coming over for a bit and getting me started... it takes a looooong time to do the wrx exhaust manifold at least, since there are 9 different places that can be done.
i was very slow and careful on the first one and it took forever. as the day went on i got more comfortable and applied a lot more pressure and just went at it.
i dont know if my job would win any awards for looks... i wasnt quite as concerned with that as just getting them opened up and matched decently well for whatever performance gains i could achieve.
anyways, on with the photos...
complete exhaust manifold, with gaskets
comparison of ported manifold versus stock untouched. notice the carbon buildup which indicates the difference in size between the actual opening and the gasket. right off the heads you want to just open these up as much as possible, but of course keep them slightly smaller than the gasket so it can seal properly
stock crosspipe versus ported one. this pipe has a flex section in it and therefore is 'sleeved'. this sleeve creates an abrupt step which you want to grind to a much smoother transition
port matching requires matching the outlet of one pipe as closely as possible to the inlet of the pipe that bolts up to it. to do this i took a sheet of posterboard on the larger of the two and cut a template of the exact opening size. i laid it onto the smaller one and basically grinded away until it matched the template. yes i know my template is ghetto but i just used it as a rough guide. also notice that i didnt open up the inlet as much as possible... thats the point here, you only want to open it as much as is needed to match the pipe it is being mated to.
and here are some finished product shots...
oh and i almost forgot to mention... arguably the biggest benefit to this mod is the mad tite weight savings yo
and since someone is sure to ask if i can feel a difference...
unfortunately i only installed the new turbo setup about 5 days prior to pulling my car apart to work on the exhaust manifold. so really, i never got that good of a feel for the car with the turbo upgrade and stock manifold. therefore i really cant tell a difference here becuase i dont have a baseline.
but most schools of thought agree that this type of work will result in slightly earlier spoolup and a few horsepower or so. nothing too crazy but slight benefits that require a good amount of time but absolutely no money (assuming you have the proper tools already)