The principle of ACM is simple, and a good deal less expensive than other systems already applied to larger capacity powerplants, with a set of electronic actuators sitting above the camshaft on the middle two cylinders controlling the movement of the valves and fuel injection.
At revs between 1400 and 4000rpm and torque loads between 18 and 74lb ft - a characteristic Volkswagen claims covers nearly 70 per cent of all driving states, the valves and injection process is shut down, effectively turning the engine into a 700cm3 twin for lower consumption and emissions, most noteably in city driving and at constant motorway speeds.
What's it like?
With 138bhp and 162lb ft, the Polo BlueGT is both eager and refined, with satisfying off the line accelerative qualities, a flexible in gear character and, thanks to a heavily overdriven seventh gear, a relaxed cruiser on the motorway. It always feels more enthusiastic than the Polo 1.2 TSI, as shown by its official 0-62mph time of 7.9sec and its 50-75mph fifth gear split of 9.5sec. Just don't expect Polo GTi levels of performance.
But its prime attraction is its economical nature. Volkswagen claims 62.7mpg, giving the Polo BlueGT average CO2 emissions of 105g/km. By comparison, the Polo 1.2 TSI is rated at 53.3mpg and 124g/km. On a 60 mile motorway run out of Amsterdam we managed 76.4mpg, proving both the worth of ACM and a series of aerodynamic tweaks brought to the new car, including bumpers, sills and rear hatch flaps brought over from the Polo BlueMotion.
The operation of ACM is virtually seamless with a display in the instrument being the only real indication of what mode you're in; there's a very slight alteration in engine character as it shuts down the valves and injection and switches into two cylinder mode. But as the pistons continue to operate within the second and third cylinders the reciprocating masses and inherent vibration does not change.
The engine never feels quite as strong in two cylinder mode as it does in four-cylinder mode, with tardier pick when you ease gently into the throttle. Push harder though and ACM switches the engine from two-cylinder back into four-cylinder mode, instantly providing the BlueGT with a full level of performance.
Should I buy one?
A game changer, then? In certain respects, yes. If the promise shown by the Polo BlueGT's new engine is any guide, cylinder shutdown is set to become an integral fuel saving feature in coming years - and not just high end models but in volume offerings, too.
Volkswagen says it is already preparing ACM for the seventh-generation Golf due out in September, suggesting the new technology ill help lessen its dependence on even costlier diesel engines as buyers once again warm to the more refined qualities of its latest 1.4-litre four-cylinder unit. Given the way it broadens the Polo's spread of scope of abilities, we wouldn't disagree.
Volkswagen Polo BlueGT
Price: £18,750 (est); Top speed: 131mph; 0-62mph: 7.9secs; Economy: 62.7mpg; CO2: 105g/km; Kerb weight: 1146kg; Engine: 4-cyl, 1395cc turbocharged petrol; Installation: front, transverse, front-wheel drive; Power: 138bhp at 5600rpm; Torque: 162lb ft at 1500rpm; Gearbox: 7-speed double clutch