If the official fuel-consumption and CO2 output figures are relevant to real-world driving (which, on the whole, they are not) then the very latest engine designs are miraculous.
They need to be, if the buyer of a 560bhp saloon capable of reaching 62mph in 4.4 seconds, 124mph in 13, and not stopping until electronics decide that 190mph is enough, is not to be excommunicated from a society the majority of whose members are not petrol heads.
So it is that the new BMW M5, the fifth car to bear this name, has a CO2 rating of 232g/km, whereas its predecessor, powered by a screaming V10 engine but producing slightly less power ("just" 507bhp) scored 357g/km. That 232 grams still puts the M5 in today's gas-guzzler bracket (it misses the tax-break cut by just 7g), 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 5.0 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 is a car of different character from any of its forbears. 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 502lb/ft of torque all the way from 1,500 to 5,750rpm. Peak power occupies a similar plateau, this one stretching from 6,000 to 7,000rpm. This is an engine whose crankshaft is keen to spin to dizzy 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 wheelarches 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 for the first time, 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, out 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 – at £73,040 – does it all.
The best M5 yet? Undoubtedly.
Audi RS5: £58,685, 450bhp, 252g/km
Ultimate A5 costs less than M5, but nowhere near as good. Great pace and sound, but dead steering, lumpy ride and little fun.
Jaguar XFR: £65,350, 510bhp, 292g/km
Supercharged 5.0-litre V8 gives almost M5-like rapidity, but greater thirst. Looks svelte, is lovely inside, great fun, but M5 has the edge.
Mercedes-Benz E63 AMG: £73,415, 525bhp, 295g/km
A twin-turbo V8, again thirstier than M5, but no faster. Another split-personality hot-rod, but not quite as engaging as the BMW.