Impreziv 2.5· Wedges' Biggest Fan!
2000, subaru, 2.5 rs impreza,
DOHC motors tend to blow headgaskets with even greater frequency than the SOHC ones, which have had plenty of issues with that in their own right. In the long run, a reliable swap is probably your best option. It will make plenty of reliable power over a period of many years and will be easy to maintain with readily available parts.
Of course, this is conventional wisdom. By all means, do what you want to do above all else. There are guys on here running N/A or with homebrew superchargers. There are spare parts turbo kits, aftermarket turbo kits like Forced Air Technologies and AVO, and there are all kinds of crazy Frankenstein swaps with EJ20's, EJ22's and EJ25's. There are even a couple H6 swaps floating around. If your goal is to be creative, then by all means turbo your EJ25D. But if cost is your concern, the small amount of cash you save in going with a homemade kit is more than likely going to be spent in maintaining (or replacing) the finished product.
From my own reasearch this is what I have found out about what you are wanting to do. Hell, I am in the same boat right now. Started ordering parts last week.
Now about your question with the piggyback. I have heard of people running the E-manage ultimate and having great results...until they want more boost. The problem with a piggy back is that It can only tune so much. There are limitations on how it controls the injectors. Standalones just offer so much more. yes they are more exspensive, but while your doing it why not take that extra steup and KNOW your engine will be safe.
I am also going to be running STi rods and pistons. & STi Turbo with a Hydra EM. Elementtunning.com has an awsome site set up for the Hydra. I would advise looking there to get a better understanding of the Hydra. They are great people if you have questions on your perticular set up you could just give them a call.
Hope this helps. Good Luck with the build!