Mazda Xedos 9 Miller Roadtest

Next time you feel a Miller draft, you are either down the pub or you have just been blown away by one of Japan's almost-secret weapons - the Mazda Xedos 9 with its supercharged aluminium V6 engine.

A car that delivers three-litre-plus power from an engine that is barely over two litres implies some serious performance engineering with looks to match. The engineering is certainly there but the looks are no more in-your-face than an M&S cardigan.

There is a hint in the oh-so-pretty 17-inch alloys but the rest is pure gravel-drive stuff that won't frighten the horses. Apart from the wheels, the outward appearance is hardly any different to the normally-aspirated Xedos 9 which the Miller replaces. Minor revisions to the front- and rear-end treatment go almost un-noticed. And the price remains unchanged as well. At 28,650 on the road, the new Xedos seriously undercuts its European rivals without short-changing on performance.

The 2.3-litre engine delivers 209 bhp which is usefully higher than the 2.8-litre equivalents from BMW, Mercedes Benz and Audi. En-route to a top speed of 143 mph, the Miller Xedos accelerates to 62 mph in 9.5 seconds, and despite driving through a non-optional auto 'box manages an impressive 28.2 mpg on the EU combined cycle.

Not only does the Mazda offer more power for a good deal less money but it also out-specifies its European rivals in comfort terms. Climate control, air-conditioning, cruise control, power roof, leather upholstery and steering wheel, electric front seats, six-disc CD autochanger, tree-wood trim - all these things, and more, are standard and matched only by the Lexus GS300 which is almost 6,000 dearer.

Slim door pillars, bags of leg and shoulder room and a low facia with a deep windscreen create a light and airy cabin ambience quite unmatched by its competitors. And the ride quality is getting on for magic carpet stuff. The drive is effortless, smooth and with just enough of the V6 sound-signature creeping into the cabin to warm the blood on a chilly morning. In all a truly excellent prestige car that I would choose in preference to any other in its class.

But is there nothing I dislike? Yes, two things. Firstly, the rather overstated Daewoo-like grille and secondly, the fact I can't afford one, despite its relatively modest price tag.

Even when pushed hard on twisting roads the Xedos 9 does not betray its straight-line performance. Ventilated discs all-round matched to ABS-linked traction control equate with its obvious potential to reward committed drivers, and the suspension offers a near-perfect compromise between ride quality and handling. It is soft enough to soak up the bumps and firm enough to resist unpredictable responses when driven with some urgency. Torsional stiffness in the body helps regulate road-holding well within the handling envelope, and there is sufficient feedback through the steering wheel to signal the approach of adhesion limits.

The secret of the almost seamless performance of the Xedos 9 is in the intercooled supercharger combined with something called a 'Miller-Cycle' engine, hence the full name - Mazda Xedos 9 Miller. The Miller bit is a variation on the theme of Otto's original cycle - suck, squeeze, bang, blow, but with the squeeze and bang bits breathed on to create a 'virtual' alteration to the mathematics of upper-cylinder design.

The efficiency of an engine has much to do with the difference in volume between the fuel/air mixture in its compressed state (when the piston is up) and its expanded state (when the piston is down).The difference between the two volumes is referred to as the 'expansion ratio', and the higher the ratio, the more efficient becomes the engine.

In theory, the more the mixture is compressed in the first place, the greater the expansion ratio, but unfortunately it is not that simple. Compress it too much and the engine knocks itself into oblivion; compress it too little and it develops insufficient power.

But a certain Ralph Miller discovered some years ago that if you tinkered with the inlet valve timing it was possible to achieve a higher expansion ratio without excessive compression - a kind of mechanical sleight of hand that works particularly well when used in conjunction with a supercharger (which pumps compressed air into the upper cylinder at about twice the normal atmospheric pressure).

The Mazda boffins took the Miller-Cycle principle, adapted it to their own needs, added a Lysholm compressor (supercharger) and the result is the world's first car to be successfully powered by a Miller-Cycle engine. The 'amplified' power it produces means that, for a given output, a physically smaller engine can be used, with consequent energy savings - the engine simply wastes less power in driving its own internal gubbins.

The net result of all this gizmology is around 10 per cent more grunt than a BMW 528i, a lower fuel consumption and 3,500 change. And as icing on the cake, the supercharged Miller-Cycle engine produces the sort of flat torque-curve flexibility that constantly defeats most turbo-powered cars, with the possible exception of the so-called 'soft', low-pressure turbos from Saab, Volkswagen and a few others.

The technical wizardry of the engine is matched to some cunning, almost subliminal, touches in Mazda's overall design philosophy. They work on the principle of 'Kansei' which means 'the quest for harmony between man and machine' and which appears to address the emotional dividend of owning and driving one of their cars. It seems to apply to the aesthetics as well as to the ergonomics - one example being a design computer that calculates the optimum way for light to reflect from the car's contours. Volkswagen ads bang on about their 'detail meister' which is good fun and probably true, but I think I prefer the Kansei approach which has a touch of the Feng Shui about it and is altogether more mystical and engaging.

A lot of fuss is being made about the Rover 75, the great white hope of what's left of Britain's mass-production motor industry. It's too late now, but I think BMW could have done a lot worse that to study the Xedos in infinite detail and do their best to replicate it at Longbridge. It may not have enough kudos for the kind of people who need to park outside your window when they come to dinner, and it may not have the pedigree of a three-pointed star, but for understated elegance and discrete performance the Xedos 9 Miller is about as good for its class as money can buy.