The last 740d was a 4.0 V8 diesel. Confusingly to people outside BMW, the new 740d is not a V8, nor a 4.0-litre. Ah. Nope, the new biggest diesel in the 7-Series range is a new super-efficient twin-turbo straight-six, and it's a 3.0-litre block, but this time not derived from the same 3.0-litre motor that you find in 30d and 35d versions elsewhere in the BMW ranges.
Still with me? Right, explanation ahoy: this new motor gets an all-aluminium crankcase and third-generation, common-rail fuel injection that's good for 2,000 bar of pressure. Piezo injectors provide the injection, and big pressure and fine control are good things. Higher pressure means bigger bangs, control means more efficient burns, the pair bring better power and economy.
And with the 740d, the power is impressive - 301bhp (the 35d produces 286bhp), and 442lb ft of torque from a lowly 1,500rpm. This translates into some really quite tidy performance figures: 62mph in just 6.3 seconds - about half a second quicker than a Golf GTI - and a limited 155mph.
Mix enough punch to annoy fast cars with a combined economy figure of a smidgen over 40mpg and a CO2 hit of just 181g/km, and you have to respect what BMW has done here. If you want a demonstration of what BMW gleefully calls ‘efficient dynamics', here it is: a fast car that also delivers on the boring-but-necessary stuff.
Spreadsheets don't really tell you enough about how this engine feels though. There's a pair of turbochargers - one little, one big - which play tag to provide quick response with big punch at higher revs. It is quiet, smooth - much more so than any 35d variant - and ridiculously punchy. If torque is what counts in the real world, the 740d has the ability to deliver it in any situation with the muscle that befits a big car.
With the UK massively intent on diesel versions of the Seven - 85 per cent of 7-Series sold in the UK are 730ds - the 740d reminds you that diesel doesn't have to be noisy, or slow, or boring, to get the kind of economy and CO2 that will make it a genuine day-to-day car. The only problem is, it makes the 730d look like the miser's choice: the mpg and CO2 are near-identical, but the 740d is way faster. Save up.