X marks the sport

What we’ve got here is a car that’s on the one hand ferociously complex and cutting-edge, and on the other hand is actually pretty simple and straightforward. And I’m not quite sure which half of the Mazda 3 SkyActiv-X’s personality I prefer.

Okay, so SkyActiv-X, what is it? Well, it’s very complex technology that allows a petrol engine to, most of the time, burn its fuel like a diesel, which theoretically results in better fuel economy and reduced emissions.

How does that work? Stay with me, this is complicated, but I’ll break it down as simply as I can.

The SkyActiv-X engine is an SPCCI unit, which stands for Spark Controlled Compression Ignition. You know how a normal diesel engine works? It compresses its fuel to the point where, as the inescapable laws of physics allow, the increasing pressure in the cylinder raises the temperature of the fuel past the point where it will burn and explode.

Petrol doesn’t do that as easily as diesel, so it’s not quite right to say that the SkyActiv-X engine burns fuel just like a diesel does.

Instead, what it does is to compress the fuel-air mixture as much as it can, right to the edge of compression ignition, and then Mazda adds a spark from a small spark plug at the top of the cylinder. This ignites a tiny portion of the fuel, but that ignition causes both a temperature and a pressure spike and — whoof — the whole lot goes up in a big explosion, forcing the piston back down the cylinder, and on goes your engine.

Why go to all this trouble? Efficiency. Not only is compression ignition more efficient than regular spark-plug ignition (hence why diesel engines are so economical) but in burning petrol this way, Mazda can also use a much higher ratio of air to fuel.

Remember the ‘Lean Burn’ Toyotas of the early nineties? Like that but with knobs on.

The upshot of all this tech is that Mazda can offer a 180hp 2.0 litre petrol engine with, potentially, the fuel economy of a diesel engine. Does it work? Almost…

Let’s talk about the rest of the Mazda 3, to which this SkyActiv-X engine has been attached, first. By heck, it’s a good looking car.

Possibly a little less so in saloon form, as tested, than as the more dramatic-looking five-door hatchback, but gorgeous even so. From some angles you could almost mistake it for the much more expensive Mazda 6 saloon, which surely can’t be a bad thing.

It’s practical too, with a very generous 450 litre boot and plenty of legroom in the back seats. It’s also, significantly, less dark and oppressive in the back than the hatchback version, thanks to a flatter windowline and a more generous amount of glass. If you’re carrying kids in the back on a regular basis, that’s worth considering.

Our test version was a Platinum Sport-spec model, with the very desirable ‘stone’ leather (off-white to you and me) seats, which would set you back at least €35,420. That seems like a lot for a relatively humble Mazda saloon, but there are compensations.

The first of which is that the interior is of such good quality, and so attractive to boot, that you won’t feel as if you’ve been overcharged. There’s a genuine sense of premium motoring here.

The second of which is that you don’t have to spend this much. As standard, any Mazda 3 comes with good equipment levels, including a heads-up display, a big infotainment screen (which now uses Mazda’s massively improved software, a huge leap forward over its previous system) and safety tech such as active cruise control and a driver attention monitor.

Finally, there’s the way it drives, which is to say it’s excellent. The steering is slightly light, but very fast across its lock and full of feel. The front end bites, hard, into corners and the whole car feels adjustable and biddable in a way that’s hard to match in the segment. Actually the only fly in the dynamic ointment is the ride quality, which is just too thumpy at times.

And the engine? Well, that’s a bit of a mixed bag. Remember how once, Toyota’s hybrid system would really only work properly when drive slowly around town, and when you took it out on the motorway, its economy just went to pot? Well, the SkyActiv-X is a little like that, but just the other way around.

Take it on a long motorway cruise, and you could very easily breach the 50mpg barrier as you barrel along, maybe even reach 55mpg — compact diesel territory.

Keep it in town though and you’ll struggle to do much better than 35mpg, and that’s in spite of the 3 having a mild-hybrid system that allows for earlier activation of the stop-start system, and which keeps the engine stopped for longer when you’re dawdling in traffic.

So it’s not quite a disappointment from the economy point of view, but just a bit more mixed than we were hoping.

Good for long-haul driving, less good for urban use, and always with the knowledge that Mazda has solidly frugal SkyActiv-G 122hp mild-hybrid petrol, and Sky-Activ-D 1.8 litre diesel options available too.

There’s huge potential in the SkyActiv-X system, but possibly we’re just not quite seeing it yet.

Maybe stick with the (excellent) SkyActiv-G 122hp engine instead for now.