Volvo’s electric-assisted XC90 didn’t deliver world-changing economy during our drive, yet it still impressed.

THOUGH it’s undeniably a technological masterpiece, there’s no challenge to driving Volvo’s XC90 T8.

The ‘Twin Engine’ title suggests something unusual, yet it’s just a put-into-gear, press-the-accelerator and head off in smooth, effortless style kind car.

More of a challenge, however, is exacting anything like the optimal efficiency Volvo cites as being possible from a $134,900 flagship model that puts an engine up the front, an electric motor at the rear plus a whole load of plug-in rechargeable batteries in the middle.

I’m not suggesting that the 2.1 litres maximum thrift cited by the Swedes for this model is impossible to achieve; check yourself into the kind of vehicle test lab where such figures are achieved and I’m sure you could tick that box.

But expecting to find it so easily on an everyday drive, in everyday conditions appears a much stiffer challenge.

A fail? Not at all. It simply means Volvo hasn’t escaped a burden borne by all plug-in electrics. It’s a pity that this car, as a promotional vehicle, had the maker-cited economy plastered across its flanks. Moments when it was actually operating as advertised were few.

Mind you, the 160km run I undertook in the vehicle earlier this week was hardly going to make supreme economy all that easy. The route I choose included a lot of open speed driving and, ahem, the tallest, steepest over-ranges crossing in the lower North Island. Exhausting stuff for any electric, despite the regenerative braking benefit the descent would bring.

Would you be happy with an 8.3 litres per 100km result? I’d hoped for a touch better, not least because the diesel car I drove to this assignment, over similar distance at similar pace (but without that huge hill), had achieved a 7.1L/100km regime from its 2.0-litre engine. Then again, there's the weight and size thing. My Subaru Outback, though hardly insubstantial and also cited as a SUV, is not as substantial as the big Swede.

And there’s no hiding that size. The scale of incredulity about this car being as theoretically efficient as the most efficient microcar on the market is in any event straight away stretched by it being what it is. A full-sized, seven-seater luxury sports utility.

Other mitigating circumstances? The XC90 had for 90 percent of its journey been asked to travel at 100kmh, with its Power mode enacted to haul that 2343kg bulk from the base of the Rimutaka Hill to its summit at 940 metres. It felt frisky, but also felt the burn. For the return leg, I did it in Hybrid: Not a lot of difference in performance, but it seemed to run leaner. Also, in hindsight, I should have employed the engine more in its battery replenishment mode, rather than mainly relying on restoring zap simply with regenerative energy from the brakes and deceleration. Burning fuel to make electrical energy might seem oxymoronic, but it’s an efficiency that makes sense when needs must.

As I say, there were several occasions during my drive when it really was as good as the label suggested. Unsurprisingly, it occurred in the city, which is patently where its electric-only operation makes most sense.

The switch to battery push will naturally occur when running in Hybrid configuration at low pace but there is also an option to wholly configure that way. Using what Volvo calls Pure mode opportuned minutes from my final destination and in a 50kmh zone; the car signaled 3kms’ pure electric range so I chanced my arm and went for it. It possibly only had about an AAA battery’s worth of zap left by the end, but making it ‘home’ on pure electric push alone still seemed a success of sorts.

Nonetheless, it seems prudent to be wary of the on-board calculus. Heading off on the drive, the computer opined I had 38kms electric-only range, which is 12km less than the car’s claimed optimum.

So why was it that, 15kms on, the battery icon was almost depleted? One major impact was the change in speed; the first part was inner-city dawdling but then I hit the motorway and had to step up the pace. When that happened, the drain was all the greater. In hindsight, what I should have done then was to break away from any electric assist, relied wholly on the engine’s push and returned to ohm-land when back in a 50kmh zone. But I didn’t.

Alternately, I could have stayed in a low-speed zone. Fair dues to the XC90, it could in theory cope. Despite its substance and five-metre length, it’s actually an especially city-friendly kind of large SUV; great visibility and a terrific suite of driver assists, including a self-park function, enhances this kind of operation.

But a city-bound SUV is a wasted machine. My drive provided coherent reinforcement of how good this Volvo is at open-road work: It’s a quiet, hugely-comfortable and extremely well-kitted and finished luxury conveyance, with tidy – if not outrageously sporty, even with R-Design suspension and tyres – dynamic traits.

And here’s another thing: It’s also powerful. The 2.0-litre petrol engine might seem puny in respect to capacity, but it’s turbocharged and supercharged; the latter acts low-down in the rev range and the turbocharger boosts top-end output.

It creates 241kW before you factor in the hybrid electric drive, which contributes another 65kW, while the combined torque is 800Nm.

Power mode combines the petrol and electric motors for maximum performance and dertainly invigorates. The combined power output is similar that from the Yamaha petrol V8 that once had top billing in the previous shape model: Volvo’s claim of 0-100kmh in 5.6 seconds seems wholly believable.

The problem with using all its energy is that … well, you’re using all its 'good' energy: The faster and harder you go, the quicker the battery depletes.

It’s not easily restrained. Soft-shoeing the throttle has only partial success because performance is strong from idle. Even though there’s not quite that effortless low-down surge you find in a big diesel, few will find the ultimate performance anything less than exhilarating, especially for a car like this. All it cannot do is sound the part: there’s no growl, snarl, rumble or bark here. As a colleague had forewarned: “It sounds like a car powered by a rather small four-cylinder petrol engine, because that’s what it is.” Quite.

It’s better to select the Hybrid drive mode and trade a little of Power’s throttle response and poke for improved economy and enhanced refinement. Either way the integration of electric and petrol power is almost seamless. The brake pedal is similarly well resolved, passing through the regenerative phase and into hydraulic braking with no discernible shift in resistance.

About that. Normally it wouldn’t be at all prudent to advise free-wheeling down the Rimutakas but, when enabled, the regenerative braking function is so strong that I found it barely necessary to trouble the brake pedal.

That regen effect returned the battery from near dead to about one quarter capacity, but it didn’t take long to deplete again on the flats. You can, of course, choose to store the electrical energy and wholly rely on the engine, but it does sound a bit strained in that mode. And, of course, it is burning more petrol then than in any other setting, potentially not as much as the next-step-down T6 model. But, then, that car costs $24,000 less. How long would it take to offset that in fuel spend?

Assuredly, some of that premium is swallowed up the snazzy add-ons – everything here from a crystal gear shifter to side steps with the cost-extra R-Design pack – but, unavoidably, the bulk of this extra financial burden is that point-of-difference powertrain.

Volvo has contained the burden insofar that the model has the new SPA scalable product architecture designed from the outset to package this electric powertrain. It’s all neatly done, of course, both in presentation and function.

A generator sandwiched between the two kicks the petrol engine quietly into life, boosts torque and charges the battery as required. The cells, housed in the central tunnel a propshaft normally calls home, feeds that large single electric motor on the rear axle that also generates electricity under braking. A control unit in the engine bay synchronises the two power sources, ensuring happy, efficient collaboration and all-wheel drive when required.

The driving mode be switched between no less than five different driving modes – Off Road, AWD, Pure, Hybrid and Power – selectable via a portrait-orientated central touchscreen or a rotary dial.

Beyond this, it operates just as effectively as the orthodox XC90, with the special drive gear making no injurious impact on the seating layout, luggage and cabin space.

It even maintains the same off-road capability as the orthodox versions and even though the XC is not designed to conquer mountains Land Rover-style, that’s no bad thing to know when you’re heading to the beach or up to the ski lodge. After all, I know of one other hybrid SUV on the market whose maker warns against taking it through deep puddles. The XC can wade streams if asked. Not that I did.

What to make of this model? Well, the XC90 is a truly premium product and a very fine SUV and the flagship trim simply amplifies that impression.

The T8 is also brilliantly engineered; the packaging of that Twin Engine drivetrain really is exceptional. The refinement and the performance is also impressive.

Also, there’s something quite cool about how Volvo doesn’t feel need to shout out those special abilities. Badging on the boot and the extra filler flap on the nearside front wing are the only external cues to what it really is.

That’s really quite subtle but, given that it failed to achieve as well as it might have been expected to, perhaps that’s no bad thing.