M260

Introduced from 2017, the M260 is the transverse half of the second-generation four-cylinder family, and it is an evolution of the M270 rather than a clean sheet — the same two-liter bore and stroke, now breathing through a twin-scroll turbocharger and exhaling through a petrol particulate filter fitted to meet the emissions rules that arrived with it. Friction was attacked in the machine shop: the bores are finished with CONICSHAPE honing, a patented process that opens the cylinder very slightly towards the bottom so the piston skirt has less to rub against.

What it is remembered for sits at the top of the range. At 190 to 224 PS in the A 220 and CLA 250 it is unremarkable; wound out to 306 PS and 400 N·m it becomes the engine of the A 35, CLA 35, GLA 35 and GLB 35 — the cars AMG built to sit beneath the hand-assembled M139, and the reason the 35 badge exists at all. Nothing about the hardware is exotic; the whole trick is that one architecture stretches from a base A-Class to something that will run with a hot hatch, which is what a modular family is supposed to do.