Either you're going to agree with me on this or you're not. I really don't mind either way. If you do, well, hurrah! If you don't, that's fine - we all have our different views. But as much as I may respect your opinion, I'm not going to change mine on this issue: as far as I'm concerned, the best engine in any currently available Vauxhall Astra GTC is the 1.4 petrol turbo, and that's all there is to it.And by the 1.4 petrol turbo, I mean the 140PS (or 138bhp) version tested here. The same unit is also available in 118bhp form, and there are several other choices in the Astra GTC range, namely 109bhp/128bhp 1.7-litre and 163bhp 2.0 diesels and, the most powerful of the lot until the introduction of the VXR, a 178bhp 1.6 petrol turbo.I should make it clear at this point that I haven't tried all of them. The 2.0 diesel, yes, the 178bhp 1.6, also yes. The others are, at the time of writing, a mystery to me. But any of them would have to put on a fine show to be able to challenge the 138bhp 1.4 in my affections.I spent a week with the 2.0 diesel last year (see review) and experienced the 1.6 during the UK media launch. The 1.4 turbo has less power than either, and that may be why I like it. Often enough I find that an engine either has a little, or a lot, too much power for the rest of the car, or it may be the other way round.On rare occasions a car comes along whose engine seems to provide it with exactly the correct amount of performance, and I think that's the case here, possibly because the GTC isn't quite as sporty as its handsome coupé lines suggest.It's not that the car is slow, incidentally. A top speed of 125mph and 0-62mph in 9.5 seconds do not suggest great drama, but as I've found both in this car and in the new Vauxhall Zafira Tourer the engine delivers very strongly, if required, from remarkably low engine speeds. The flexibility is sufficient to allow either enthusiastic or gentle driving with a minimum of gearchanging, and however much you enjoy changing gears you must admit that too much of it can become tiresome.The less powerful 1.4 turbo has exactly the same 47.9mpg combined fuel economy and 139g/km CO2 emissions (meaning annual VED payments of £115 from year two onwards) but will surely use less fuel in real life, and is £400 cheaper to buy in SRi trim.The diesels are even more economical, as you might expect, the 1.7-litre ones costing just £30 a year to tax, but as you might equally expect their list prices are significantly higher. The GTC's suspension doesn't seem to have been adequately adjusted for the weight of a diesel engine, though, making these versions that crucial bit less enjoyable to drive on a winding country road. Engine 1364cc, 4 cylinders Power 138bhp Transmission 6-speed manual Fuel/CO2 47.9mpg / 139g/km Acceleration 0-62mph: 9.0 Top speed 125mph Price £20,345 Details correct at publication date