This is probably one of the most asked questions regarding the XT6. Yes you can - if you have enough money and time for a custom build. Turbocharging the ER27, although not ever clearly documented, has allegedly been done. It is reported that a turbocharged XT6 placed 7th in the Grass Roots Motorsports $2002 challenge, although its recorded net times were disappointing due to mechanical failure during one of the runs. It has been discussed at length and at this writing there are a few forced induction projects underway. In addition to custom turbo builds, at least one owner is pursuing a supercharged path. The exhaust manifolds from the EA82T (the turbo four) seem as if they’d match up with the six, due to the fact that two of the six’s exhaust ports meet as one (so there are only two pipes coming off each of the ER27’s headers). This may or may not be true, however, and custom piping might work just as well or better than a manifold transplant.
As for the turbocharger itself, the unit from the EA82T seems to have a rather small inside diameter and might not be the best choice for maximum power. A more efficient yet more powerful unit from an aftermarket manufacturer might be a better option. Certainly the ability to force feed more air into the engine in a more efficient manner wouldn’t be beyond the scope of reason, given today’s glut of aftermarket turbo support. There are other factors to consider in addition to which size and/or brand of turbo you want to slap on your ER27.
The pistons used in the EA82T are the same bore (92mm) as those found in the ER27, but they have a 8.5:1 compression ratio whereas the pistons found in the ER27 are 9.5:1 units. Due to the higher compression ratio, most likely you could only run relatively low amounts of boost - say, 7 lbs maybe? If you were to turbo your ER27, you might do well to scavenge the pistons from an EA82T. With the proper pistons, you could probably run higher boost and relatively normal octane gas (92 octane or higher). The transmissions in the XT6 are said to be much more sturdy than those in today’s WRX - capable of handling as much as 400HP! - but it is also rumored (much to the chagrin of most drivers) that the 4EAT auto tranny is the strongest. Other issues warranting consideration are fuel management and delivery, exhaust gas temperatures, detonation, etc.