Late last month our spy photographers captured images of the still-in-development Audi RS5, and now word has leaked that the car will make its world debut at the Detroit Auto Show in 2009. Unfortunately, however, it will not be accompanied by the 2009 RS6, which is off the table for American sale.

Emissions testing is the culprit, since the RS6's massive twin-turbo V10 powerplant just isn't clean enough to make a reasonable business case, reports Edmunds. That means the hottest of hot family sedans will be staying out of the states for its current iteration. Its coupe cousin, the RS5, however, will be coming to America and so too will the expected 2012 next-generation RS6, according to Jens Koch, Audi's project manager for the RS6.

The next-gen RS6 will slay the current car's dragons of heavy weight and hefty fuel consumption with a revolutionary new design, says Koch. Until then, however, Americans will have to make do with the RS5, which will be closely followed by the RS4 - a brutally potent sedan in its own right.

Powertrain options for the RS5 remain cloaked in secrecy despite the essentially nude spy photos of the car in testing. One of the primary options - and a likely one given the status of Audi's U.S. emissions plans - is to take the 4.2L V8 from the RS4 and tune it a bit more violently, for about 450hp (335kW). Pairing the V8 with a dual-clutch S-tronic gearbox would also make sense given the RS5's market position.