The WRX has, for the longest time, used a turbocharged EJ engine, as has the WRX STI. The EJ engine has been around since 1989, it is a DINOSAUR of an engine and has been in dire need of replacement. That's why the Legacy GT is currently dead for North Americans. There are some EJ components that are interchangeable between non-turbo EJ and turbo EJ engines, but it's not a lot.
The 4th generation Impreza (on which the Subaru XV is based on) does NOT use an EJ engine, and uses the FB engine (Subaru's 3rd generation economy
4-cylinder BOXER Engine) instead.
However, the FB engine is designed more for fuel economy than performance. Unlike the EJ engine (Subaru's 2nd generation 4-cylinder BOXER Engine), almost no significant parts are interchangeable with the FA engine (Subaru's 3rd generation performance
4-cylinder BOXER Engine) found in the BRZ and 2014 Forester XT.
EA = 1st gen 4-cylinder
EJ = 2nd gen 4-cylinder
FB = 3rd gen economy 4-cylinder
FA = 3rd gen performance 4-cylinder
FB engines in use so far:
FB16 - used in markets where the Impreza and XV has a 1.6L engine standard
FB20 - standard Impreza and XV engine in North America
FB25 - MY2013+ Legacy and Outback (BM/BR chassis), MY2011+ Foresters (both SH and SJ chassis)
The North American market turbocharged Subarus have had, for the longest time, unequal length headers. Often called the "boxer rumble", it is actually mostly due to the unequal length headers, but the unusual manner of firing order aids the rumble.
From the mid-1990's onwards, all non-turbo Subaru vehicles have been sold with equal length headers. They sound more like ordinary 4-cylinder engines, but the unusual manner of the firing order still gives them a unique sound.
From the FB and FA engines onwards, it seems ALL Subaru vehicles, regardless of turbocharged or not, will now have equal length headers.
For those with the misconception that all Subaru engines sound the same, behold two videos that depict the difference in sound through equal and unequal length headers:
The FA20 in the BRZ, as most can already tell, has equal length headers. As I had anticipated, the FA20 Direct Injection Turbo (DIT) found in the 2014 Forester XT also has equal length headers. Now the equal length headers the Japanese market turbo engines have hogged since the 2000's are available worldwide from the factory, as shown with this video of a 2014 Subaru Forester 2.0XT