OM668

The W168 A-Class of 1997 was designed around a sandwich floor: the powertrain sat on a steeply inclined subframe so a frontal impact would push it beneath the raised cabin floor instead of through the bulkhead. That geometry dictated the engine, and the OM 668 was drawn for it — 1,689 cc, aluminum, sixteen valves, the intake camshaft chain-driven and the exhaust cam geared to it, common-rail injection and a turbocharger on every version. When it appeared it was the smallest diesel Mercedes-Benz had ever put into production.

It was sold in deliberately separated states of tune. The A 160 CDI opened at 60 PS without an intercooler; the intercooled A 170 CDI made 90 PS; after the 2001 facelift the pair became 75 and 95 PS. The same engine carried the Vaneo, the tall five-seat van built on A-Class underpinnings, until 2005, by which point the second-generation A-Class had moved on to the OM 640. Its legacy is less the engine than the layout it made possible: a small Mercedes diesel that could be laid almost flat and still meet the crash case the car had been conceived around.