From Road & Track:

Unlike the 911, which is using a 3.0 liter flat-six in both the Carrera and Carrera S, just with different turbos, the 718 twins will have a 2.0 or a 2.5 liter turbocharged flat four. The 2.0 in the base cars will have 300 horsepower and 266 lb-ft of torque while the 718 Boxster S will have a 2.5 liter flat-four turbo with 340 horsepower and 295 lb-ft of torque. There could also be a GTS version coming with 365 horsepower.

In the Facebook comments, I already see people equating the upcoming 718 engines with Subaru EJs.  Now, when has Porsche ever not blazed their own trail?  Porsche will almost certainly ensure this engine will generate glorious (or at least non-nasty) sounds.  Subaru’s trademark sounds are due to the EJs running unequal-length headers.  I highly doubt Porsche will do something stupid like adopt unequal length headers, especially if they opt to use twin-scroll turbochargers.  With luxury-sport cars such as these Porsche variants, they’re going to ensure the car sounds like it looks…fast, powerful, and sleek.