Mercedes-AMG is reportedly prepping a new model line based on the new Mercedes-Benz 'M256' straight-six petrol engine.

As with most models in the AMG and Mercedes-Benz ranges, the numerical suffix bears no relation to the engine's displacement, instead it serves to indicate where within the power and prestige hierarchy the car fits.

Sitting below the 63 range and its 4.0-litre twin-turbo V8, the new 53 models will be powered by the company's 3.0-litre inline six-cylinder petrol engine, which was unveiled last November.

According to Automotive News, the first model to gain a 53 model will be the next-generation CLS. In the four-door "coupe", the straight-six engine will be assisted by an electric motor, with total system output said to be around 320kW.

If true, the CLS53's power figure lines up exactly with the recently detailed S500, which features a 320kW/520Nm variant of the 3.0-litre straight-six. The S500 also includes a 49V integrated starter/alternator that can provide an extra 16kW of power and 250Nm of torque when required.

The next-generation CLS is expected to make its debut next year, and was last spied undergoing testing in March this year. A report earlier this year indicated the next-generation CLS may not be offered with V8 engine in order to give the AMG GT sedan its own market niche to inhabit.

Should this prove to be the case, the CLS53 will be the range-topping model in the new CLS range.