Turbocharged FA20 (D4-S)
According to Motor Trend editor in chief Edward Loh, Subaru has confirmed that it'll be building a turbo version of the BRZ's FA20 engine.
Subaru hasn't confirmed yet that it'll be putting it into the BRZ. FA20 is a new engine in Subaru`s lineup, which could replace the FB series. The new engine could probably find its home in WRX/STI for 2013.