Well with so many people talking about the hybrid engine set up I thought I would take the time and try to do a write up to answer most of the questions that so many might have about this engine set up. This really concerns people with the 02-05 WRX with the EJ205 engines. Many people have ran this set up which one of those people includes myself, I love my set up and it works very well. In this little write up I will give some pointers and other web sites to help people out as much as possible.
What to start with? STI shortblock EJ257, you can pick these blocks up for under $2,000 and comes with new block, pistons, rods. and crank already assembled. Below is a really good place to deal with and comes with a free gasket kit.
Now by bolting on your stock 2.0 heads on a EJ257 block you are going to raise your compression, so you will want to buy thicker head gaskets Good choice to go with would be the Cometic .051 to lower that compression ratio back down to 8.5:1 or so depending of if you decked your heads. As for strapping the heads down it would be also a good choice to go with a set of ARP head studs just to be on the safe side.
Now the issue with this short block is the pistons are known to crack, so I strongly suggest that you put a nice set of forged pistons in there for example short skirt CP forged pistons. Since your already looking at the pistons and they are easy to take out thats when spending that little bit of extra money will save you in the long run.
Moving onto the heads you have a number of options what to do here. You will really really also want to send your heads out and have a head job done on them and also have your heads P&P while the heads are at the machine shop put stiffer valve springs in there as well. The reason for stiffer valve springs is cause your really going to want to have different cams in there unless you don't like to make power after 5,000rpm's. This is where you have alot of options to select the right cams for you, I suggest you call your tuner and tell him what your goals are and he can help you with the right cam choice.
As for a turbo same story with the cams, you have to ask your self "what do I want out of this car" I wouldn't go with anything smaller than a 18g or else your just going to want to upgrade to something bigger right away.
Fuel wise, goes along with type of cams and turbo you are going to choose, some people send there stock injectors out and have them redone but really all they are doing is cutting the ends of the injector tip off haha. Some choices to go with are "Power Enterprise" "RC" "Deatsch Werks" there are more out there those are just the most popular brands.
After you do you build and pick your cams and turbo and all and take your car to the dyno to have it protuned you will be very happy with going with the hybrid engine.
If there is anything anyone else wants to add feel free, but i just thought I would do this little write up and maybe help some people out.