A few weeks ago when I drove a petrol-powered version of the new Mazda CX-5, I was pretty impressed with the 2.0-litre SkyActiv-G engine under its bonnet.
I was fascinated to learn that it has an unusually high 13-to-1 compression ratio so it can deliver improved torque, better fuel economy and fewer emissions.
Up until now, this sort of compression ratio just didn't happen with petrol engines, because the raised thermal efficiency tended to cause knocking and an associated loss of torque.
In developing its latest SkyActiv technology, however, Mazda overcame this by designing lightweight pistons and installing a unique exhaust system.
As a result, the SkyActiv-G engine is about 10 per cent lighter than the Mazda engine it replaces, yet develops 113 kilowatts of power and 198 Newton metres of torque, and offers average fuel consumption of 6.4 litres per 100 kilometres.
And then last week, I had my first taste of the diesel-powered version of the CX-5, and I'm even more impressed with the 2.2-litre SkyActiv-D engine under the bonnet of this model.
That's because, in direct contrast to what has been done with the petrol power unit, this engine has a 14-to-1 compression ratio which is the lowest in the world in a diesel-powered passenger car.
Up until now, this sort of compression ratio just didn't happen with diesel engines, because there was a danger compression-ignition temperatures remained too low for reliable cold starts and efficient cold-temperature operation.
But Mazda met that challenge by installing ceramic glow plugs to better heat up the combustion chambers for cold starts, special injectors to better control the combustion, and introducing variable valve lifts for the exhaust valves so hot exhaust gas can re-enter the chambers after engine starts, which also helps raise temperature.
The engine also features two-stage turbocharging for a better spread of torque right through the revolutions range.
This really is a special engine, and it is interesting to note that the lower compression puts less strain on the various components, which means Mazda has been able to use an aluminium block and lighter pistons and crankshafts, so the engine can be a lot lighter - and that in turn means it is more responsive and more economical.
It's good to drive, too.
When the CX-5 is cold, there is a slight delay before the engine kicks into life after you press the push-button start, but from that point I didn't notice any lag or cold-weather lack of performance at all.
The engine offers maximum power of 129 kilowatts at rpm, and the top torque is a hefty 420 Newton metres at 2000 rpm - which incidentally is twice the torque at half the revolutions of the SkyActiv-G petrol engine - and with the two-stage turbocharging, it will maintain that heft right through to a 5200 rpm red-line.
The diesel CX-5 I've been driving is the top model in the range, the $55,990 all-wheel-drive Limited.
For the price, it is highly specified, with standard items including adaptive front lighting, daytime running lamps, power sliding- and-tilt sunroof, leather trim, heated front seats, a driver's seat with eight-way power adjustment, smart keyless entry, a premium nine-speaker audio system, and the safety of front and rear parking sensors, blind-spot monitoring, and a lane departure warning system.
The model also has big 19-inch wheels with 225/55 tyres, which combine with the permanent all-wheel drive to help make the Limited feel secure on the road.
The engine, which like all CX-5s has automatic stop-start, is mated to Mazda's very good SkyActiv-Drive six-speed automatic transmission. It's not exactly a dual-clutch auto, but it does have a full-range direct-drive torque converter with a full-range lock-up clutch for all six gears, which makes it very direct in its operation.
The auto in the diesel vehicles is also larger than that aboard the petrol models, so it can better handle the extra torque.
All the CX-5 models have identical bodyshells, with lines inspired by Mazda's soul-of-motion design strategy that has produced a variety of beaut concept vehicles.
The ride is quite high which means visibility is excellent, and there is very good room front and rear.
Cargo room is a relatively tight 403 litres when all the seats are in use; but, in good SUV style, this can be expanded to 1560 litres when the back seats are folded down.
A few weeks ago I really enjoyed my time behind the wheel of the front-driven petrol-engined GSX model, and now I've specially enjoyed my experience with this AWD model with the new-age turbo diesel.
Of course, you gets what you pays for, and this Limited CX-5 is considerably more expensive than the base models, but it still represents very good value for the money.
- Taranaki Daily News