An iWire PSA - Before swapping your drive by wire turbo engine with a different turbo engine, make sure the Camshaft Position Sensors match!
A common scenario we get contacted about would go like this.
"I have an 06 STi and the engine blew up and now I want a JDM STi. Because they are both STi, I figure it'll be a plug and play swap."
If you have a drive by wire (DBW) engine you can not put in a non drive by wire engine because the cam position sensors are different. The DBW model engines use a 3 wire camshaft sensor at the back of each head while the JDM STi uses a 2 wire camshaft sensor for the back of each head. Without the cam position sensor the ECU doesn't know what to do.
So what is the solution? Unfortunately there really isn't one.
Some people have modified the heads for the larger diameter 3 wire cam position sensors and swapped the original DBW camshafts (the non DBW camshafts have a different number of lobes), but this is a tricky proposition mechanically and defeats the purpose of putting in some of the JDM 2.0 engines like the STi with it's ability to rev higher.
If you have a drive by wire turbo car (WRX, STi, Legacy, or Forester), then your replacement engine needs to be a drive by wire platform as well so that the cam position sensors will match. The original intake manifold and harness will bolt to the new engine so there aren't any issues with the wiring.
How can I tell which camshaft position sensor my engine has?
The best way to tell which sensor you have is to look at the back of the engine and see if the sensor has 2 or 3 pins. The 2 wire camshaft is a cable throttle car while the 3 wire camshaft is a drive by wire car.
What about a dual AVCS engine, it's drive by wire right?
Although we don't generally recommend it, it would be a solution since at least it has the proper cam position sensors, so in a pinch it would work and certainly a better option than using a non drive by wire platform. It will require ignoring the exhaust side cam position sensors or swapping them to non AVCS camshafts but at least the car will run.