Incidentally, that '15-'21 has direct inj... It is not "dual-injected". When considering purchase of the WRX I gave thought to how I'd de-carbonize that engine at interval... and when I peered-in to the underhood area I realized just how much work it'd be to access the intake manifolds for removal, etc, to do that work, and how lousy it'd be to do the walnut shell treatment. That scared me. I ended up buying a Mazda6, admittedly absolutely not in the same performance realm, but very easy for underhood access, for the same operation.Yes, and the standard WRX (with FA20 engine as opposed to the old EJ25) has had the equal-length headers since 2015 model year.
You can still hear the burbly character of the boxer engine under certmain circumstances, but, by and large, it sounds like any other 4-banger.
Do the '15-21's, the WRX's, have a carbonning-up issue? I heard there may be one...?