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. 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 at the back of each head. The ECU doesn't know what to do without the cam position sensor.
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 its ability to rev higher.
If you have a drive-by-wire turbo car (WRX, STi, Legacy, or Forester), your replacement engine must be a drive-by-wire platform so 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 be 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.
What about EJ205 Forester Engines with Drive-By-Wire?
Unfortunately, these engines are the exception to the rule. They happen to be drive-by-wire, but they come with 2-wire cam position sensors. These engines would be treated like a WRX EJ205 with cable throttle, so they are not a suitable replacement for typical USDM drive-by-wire single AVCS applications.