We've been hearing rumors and ruminations on the upcoming smaller Porsche roadster, dubbed tentatively the 550 after its historical inspiration, for what seems like years now (because it has been). This week, there is some equally tentative confirmation that the four-cylinder boxer engine that will power it is now under development within the walls of Weissach.

Engineering a four-cylinder version of Porsche's legendary boxer engine might not seem such a hard task--even without the decades of previous four-cylinders to draw on, you could simply lop a couple of cylinders off the existing sixes, right? That's basically what Porsche is doing, though it will no doubt have to optimize the build for the desired power output and driving characteristics sought for the final product.

Autoweek reports the new four-cylinder will be based on the current 2012 911's boxer six, including the same 4.65-inch bore, which hints at a possible displacement of up to 2.66 liters, though with a slightly shorter stroke, both 2.0-liter and 2.5-liter variants are possible.

With the benefit of forced induction and direct injection, the engine could make as much as 380 horsepower, though we expect much tamer, 200-300 horsepower versions to be the norm for the range.

For more on the sub-Boxster roadster's back story, read here.