So, this is it then, the new BMW 630i, launchpad for the lightest six-cylinder engine in the world. Probably. In fact, when pushed, BMW bosses admitted they didn't actually know the weight of Mazda's baby 1.8-litre V6 from the MX-3 of the early '90s (the smallest six-pot I could think of at the time of asking) but they're still mighty proud that their new 258bhp 3-litre engine, fully dressed, stops the scales at a mere 130kg. Compare that with the single-cam, all-aluminum Rover V8 (RIP), which also had a reputation for lightness and which produced similar power, yet weighed in at 230kg.