If the official fuel consumption and C02 output figures are relevant to real-world driving (which, on the whole, they are not) then the newest engine designs are miraculous.
They need to be: if the buyer of a 420kW saloon capable of reaching 100km/h in 4.4 seconds, 200km/h in 13, and not stopping until electronics decide 307km/h is enough, is not to be excommunicated from society, the majority of whose members are not petrolheads.
So it is that the new BMW M5, the fifth car to bear this name, has a C02 rating of 232g a kilometre, while its predecessor, powered by a screaming V10 engine, but producing slightly less power ("just" 378kW), scored 357g/km.
That 232g still puts the M5 in today's gas-guzzler bracket, but it's more economical than the average Cortina ever was. Officially.
Today's eco-engineering vogue is for downsizing and turbocharging, and the M5 is, in its way, right on message.
Its engine has just eight cylinders, with a capacity slashed from the previous car's 5 litres to a demure 4.4. And it has two turbochargers.
So far it sounds similar to the engine used in the M versions of the X5 and that monstrous motor-mutant, the X6, but the M5 gets new cylinder heads with BMW's clever Valvetronic system.
This replaces normal throttles with variable lift. This way, the inlet valves can do more efficiently what throttles used to do.
The new M5 you see here will land in New Zealand in February. It is a car of different character from any of its predecessors. It has several characters actually, all authentic and all novel in an M5.
Key to these are the smooth-shifting, six-speed, double-clutch gearbox, individual controls for engine and gearbox responsiveness, steering weighting and suspension tautness, and the fact that the engine produces a massive 700Nm of torque all the way from 1500 to 5750rpm.
Peak power occupies a similar plateau, this one stretching from 6000 to 7000rpm. This is an engine whose crankshaft is keen to spin to dizzying heights, but the numbers suggest you probably don't need to.
As before, there are hefty wheels to transmit the energy to the road, slightly stretched wheel arches to cover them, ample frontal air intakes, vents in the sides of the front wings and a quartet of tailpipes.
All are outward signs that around 80 per cent of the M5's components are either altered or replaced relative to a regular 5-series.
But this doesn't look an especially menacing car and, if you set those buttons to Comfort (steering and suspension) or Efficient (engine) before you set off, you would almost think you are in a normal 5-Series.
At the opposite extreme are Sport Plus settings. With all parameters Sport Plussed, the M5 grows a fine pair of horns. Now, a gentle prod on the accelerator pedal sends the BMW lunging forward with a deep, hard-edged rumble.
With the transmission in automatic D mode, this is accompanied by a downshift, plenty of engine revs and some dramatically sputtering sound effects with each subsequent upshift, but if you're in manual mode, with steering-column paddles to control the gears, you can stay in a high gear and still the M5 erupts into ballistic thrust.
So yes, you can make the engine spin quickly but, unlike with previous M5s, you don't have to. This spread of instantly accessible energy makes this big, heavy car uncannily wieldy.
Later, on a track, I could analyse this with more clarity. After braking and turning into a corner, firm acceleration would push the front end on to a wider line, so you worry you might drift too far to the edge of the track.
The instinct is to ease off a bit, but that is the wrong response. Instead, you accelerate harder, which edges the rear wheels out and points the nose back in. It's a delicious feeling, all controlled with your right foot.
No other large, ultra-fast saloon is as interactive as this, and it's a joy. Luxury saloon, racetrack toy or any shade in between, the new M5 (£73,040 in Britain - $149,345) does it all.