Subaru engine, Which one Options

[r_towle]

Not trying to be a dick, but please (pretty please) answer just my specific question because I am old, I don't understand all these numbers, and I want to start shopping.

What is the biggest, most horsepower, turbo, gas, Subaru engine that easily ( no drive by wire or anti theft stuff) can be swapped into the car?

[DBCooper]

Biggest and baddest? That would be the STi 2.5 liter EJ engine with 300 hp, but Rich, you say you're really old? And feeble? Then that might be too much power for an old guy, so next up would be a later 2.5 WRX turbo EJ with 230 hp, or the later EZ30 six cylinder (gear driven cams) naturally aspirated with about that same power or more. There's a Wikipedia article that lists them all by year, engine model numbers, displacement, hp, etc. (HERE)

Just a point, though. The immobilizer and drive by wire stuff only comes into play if you use the OEM Subaru ECU, if you go aftermarket it's a non-issue. There are plusses and minuses of aftermarket vs. OEM ECU's, but going aftermarket gives you a lot of flexibility with all the different systems. Using a later engine with an OEM ECU gets you past the drive-by-wire and immobilizer issues but then locks you into a lot of stock systems that need to be brought over from the donor car.