Our last review of a Ford Focus fitted with the three-cylinder 999cc EcoBoost turbo petrol engine was published in mid-June (here it is), and at the time we mentioned that that was a very short test. This one - of a car which differs from the first only in that it's in Zetec S rather than Titanium X trim - extended over a week and gave us a chance to see what the smallest-engined Focus is like to live with.In several respects, of course, it's just the same as any other Focus. More than a year on from its introduction to the UK market it still looks fresh, and as with Fords in general these days it feels very well put together - not quite to the extent of a Volkswagen, perhaps, but more so than a Renault or Vauxhall.Then again, you do have to put up with very limited space for rear passengers, truly awful rear visibility and limited steering lock which gives the Focus an amazingly large turning circle. All three should be attended to, though that's not to say that they actually will be.The little EcoBoost engine (the smallest, as we've said before, that Ford has built in around half a century) is the result of an attempt to lower official CO2 emissions on the EU test which, although it's not an effective way of reducing carbon dioxide into the atmosphere in real life, is nevertheless the best anyone has come up with so far.If you build a car with a petrol engine of a certain size, and then replace that engine with a smaller but turbocharged one producing the same maximum power, you end up with better official fuel economy and CO2 figures without loss of performance. That's what Ford has done here, and its efforts earned it the overall 2012 International Engine of the Year award.Official figures do not, however, guarantee what you'll achieve yourself. According to the EU test, the 1.0 EcoBoost will average 56.5mpg, That could probably be matched with a bit of care, but if my experience is anything to go by you probably won't exceed 50mpg very often.This means that the 114g/km CO2 rating isn't accurate either, but fortunately for your budget you'll be taxed as if it is, so annual VED payments from year two onwards will be just £30.The engine is very quiet most of the time, and when pushed hard it sounds great, as all three-cylinder units do. As mentioned in our previous review, its light weight also makes a big difference to the dynamics of the Focus. It changes direction more easily than any of the four-cylinder versions do, so it feels quite a bit sportier even though the ride is also better. If you've ever wondered how significant weight is to a car's behaviour, you should try this one.But I must admit I'm being kind here. Everything in that last paragraph is based on my experience during the test of the Titanium X. The Zetec S should have been better still, particularly because it's fitted as standard with sports suspension, but in fact it was horrible. Why? Because it was fitted with the £400 optional 18" wheels and low-profile tyres which are a complete disaster on every current Focus. They made the EcoBoost feel sluggish and uncomfortable, and are best avoided. Engine 999cc, 3 cylinders Power 123bhp Transmission 5-speed manual Fuel/CO2 56.5mpg / 114g/km Acceleration 0-62mph: 11.3 seconds Top speed 120mph Price £19,195 Details correct at publication date