Tech Talk: Turbocharged engines skew the sums

Fuel ratings are only useful to an extent - the argument can be made that both turbocharging (and hybrids) are better at meeting governmental standards than improving real-world fuel economy.

The problem with fuel ratings are that they bear little resemblance to real-world driving. More delusion than reality, most drivers can't hope to match the numbers manufacturers attain for their cars in the government-regulated tests.

Of course, everyone - at least everyone save the dedicated high-miler - realises that the boasted numbers are pure flights of fancy. But, goes the rationalisation, they at least give us a relative basis of comparison; even if the numbers are 10, 20 or even 30 per cent optimistic, they are equally skewed so we at least know that car A or technology B is more frugal than that other.

On a limited basis, that's probably true. Compare a Toyota Yaris with a Hyundai Accent and, since both feature small petrol-fuelled engines with manual transmissions, the correlation is at least valid. Where the convenient comparison starts falling apart is when you compare new technologies with conventional. After all, the reasoning behind the mass switch to turbocharging and hybrids is that these higher-tech alternatives are less wasteful than what we currently drive.

And, indeed, they are. At least according to official figures. Ford's EcoBoost V6 in its F-150, for instance, is touted by the American EPA to get eight per cent better fuel economy than the V8 it supplants. The theory makes sense: make the engine smaller so it sips fuel under light load and then turbocharge it so it doesn't sacrifice performance.

Out on the open road, it's not quite so simple. Dip into all those turbocharged ponies and the fuel mileage is seldom superior; in fact, Consumer Reports recently found that the 3.7L EcoBoost V6 in the aforementioned F-150 pickup did not increase real-world fuel economy over the 5.0L V8 it's supposed to replace (it does tow better, however, which explains its popularity).

Indeed, the argument can be made that both turbocharging (and hybrids) are better at meeting governmental standards than improving real-world fuel economy. A cynic (that might be me) would contend that they are only about meeting regulations. North American testing typically emphasises urban driving (a boon to hybrids) and light-load open road motoring (where turbos are especially effective). Drive harder - and I don't even mean tyres scorching - and their fuel economy suffers dramatically. Hybrids, for instance, have not made much of an impact in Europe. Their petrol-powered motors, despite being smaller, are not particularly frugal at autobahn speeds. It also helps explain the European preoccupation with diesels; the harder you drive an oil-burner, the greater is its advantage over a petrol engine.

With improved fuel economy and reduced emissions will come some sacrifice.

As much as it forces us to face that reality, it behoves us to understand the fantasies we're being fed. Environmentalists want us to completely change the way we live. EV proponents expect you to abandon the freedom that automobiles have promised for more than a century, namely to go where you want, when you want. Hybrid manufacturers need you to dramatically alter the way you drive if their wares are to be optimised. Those pimping turbocharging as a panacea for profligacy merely want you to suspend reality.

And we the consumer? Well, we don't want to change a thing.