Inline For The Throne

Mercedes-AMG says its newest engine is the most powerful road-going production inline-four yet. So, what makes it such an engineering feat?

- Chris Thompson

REMEMBER THE LAST TIME you saw ‘only milk and juice come in 2.0 liters’ sticker on the back of something like an XR6? Well, it turns out a 2.0-liter engine can now use that exact milk to, well, eat an XR6 for breakfast.

See, the incoming AMG A45 S is leaving the already supercar-killing power of its predecessor well truly behind thanks to AMG’s new M139 engine. At 1991cc, the turbocharged engine is effectively the same capacity as the likes of Honda’s 228kW Civic Type R engine, but Affalterbach engineering know-how (and likely the A45 S’s higher expected price) has resulted in an incredible 310kW being pumped out of those four friction-reducing Nanoslide-coated cylinders.

A couple of minor changes to the dimensions don’t give the power game away. An extra millimeter of bore makes for 83.0mm while the stroke remains 92.0mm, but the compression ratio is up to 9.0:1 from the preceding M133’s 8.6.