Audi A1 and A3 to get half an engine

11 March 2013

Audi A1 1.4 TFSI with Cylinder on Demand technology

An interesting new engine I drove recently in the latest Volkswagen Golf – a 1.4-litre petrol engine developing 140PS (138bhp) – has had some Audi badges glued on and been added to the options available for the popular A1 and A3 ranges. The engine’s remarkable trick is that it can run on only two cylinders rather than all four, operating much more efficiently as a result, whenever demands are light.

If the engine is spinning at between 1,500rpm and 4,000rpm, and torque demands are below a third of the full-bore 250Nm, the engine can shut down combustion in the middle pair of its four cylinders. This increases the workload placed on the remaining two pistons, allowing them to operate in a more effective part of their duty cycle.

In VW vernacular this system is called Active Cylinder Technology or ACT, but in the new Audi application it’s called Cylinder-on-Demand or CoD. Of course Volkswagen and Audi are part of the same Germanic empire that stretches from Bugatti and Bentley to Seat and Skoda, so a good piece of tech seldom ends up in just one brand of car. But to date, CoD technology in the Audi range has been limited to the pricey and sporty end of the brochure, in models like the RS6 Avant, RS7 Sportback and S8 sports saloon.

Naturally, dormant cylinders can’t ever physically take a break – all pistons always remain connected to the crankshaft and must keep pulsing up and down whenever the engine is spinning – but their fuel supply can be cut off and their valves kept closed to keep energy losses to a minimum.

Engine cutaway showing Cylinder-on-Demand actuators

The changeover from one mode to another is completed in just one revolution of the new engine – taking no longer than 35 milliseconds – and is orchestrated by all sorts of hidden cleverness with the camshaft, fuel injection and throttle systems. Having driven the Volkswagen version I can vouch for the fact that the transition between four and two cylinder operation is entirely smooth and seamless. If there weren’t a little lamp on the dashboard to discriminate between 2- and 4-cylinder running you’d never be able to tell.

However, you might appreciate the difference at the fuel pumps. In the three-door A1, official fuel economy comes out at 60.1mpg, with CO2 output of 109g/km. There is only a slight penalty for choosing the more practical five-door A1 Sportback in its sportier S-Line or Black Edition variants, where the numbers come out at 57.6mpg and 113g/km. These results are paired with a 0-62mph sprint of around eight seconds, the exact timing depending on the model and transmission.

Surprisingly, the larger A3 can match the A1’s most frugal figures when fitted with the 1.4 CoD engine and manual gearbox, returning the same 60.1mpg and 109g/km for its three-door version – identical, incidentally, to the 1.4 ACT version of the Golf. The even bigger A3 Sportback manages a still noteworthy 58.9mpg and 112g/km.

Audi A3 1.4 TFSI with Cylinder on Demand technology - rear view

In other words, you get the promise of diesel-like efficiency without ever having to manhandle an oily diesel fuel pump or, indeed, churning out nasty micro-particles of harmful soot.

The drawback is a diesel-like price premium of £850 over the standard 1.4 TFSI engine, which admittedly delivers a lesser 120bhp. Prices for the A1 with CoD start at £16,740, or at £20,055 for the A3.

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