WOLFSBURG, Germany – Volkswagen is not alone in charting multiple paths to curtail fuel consumption. Diesel engines remain popular in Europe, so it seems fitting that VW’s two latest fuel sippers – one intended for high volume, one not – integrate oil burners.

The futuristic XL1 2-seater with polycarbonate windows, natural-fiber instrument panel, enclosed rear wheels and dihedral scissor doors is a technological moon shot for its carbon-fiber monocoque, 2-cyl. engine, 1,753-lb. (795-kg) curb weight and low drag coefficient of 0.189.

VW will build only 250 XL1s at its plant in Osnabruck, Germany, and the car is expected to be available on lease in Europe.

On the other hand, the Volkswagen GTD, a sporty derivative of the redesigned seventh-generation Golf compact with a high-output version of the all-new EA288 2.0L TDI 4-cyl., is more affordable, accessible, production-feasible and, truth be told, much more enjoyable to drive.

The car already is on sale in Germany with a starting price of €29,350 ($39,136) with a manual transmission.

Sadly, neither the XL1 nor Golf GTD has the green light for sale in the U.S., but it’s wholly appropriate to dream.

These two vehicles, lightyears apart within the brand’s product universe, are remarkable for a number of reasons.

One against the other, the XL1 wins for space-age styling, advanced materials and for demonstrating what is possible when German engineers are given a huge budget, a long leash and an overwhelming target.

The GTD trumps its smarty-pants brother with world-class chassis dynamics, a first-rate interior and the ability to be had by most enthusiasts shopping for a new car. And springing from VW’s massive new MQB architecture, the Golf GTD should be profitable, unlike the XL1.

On the powertrain front, the XL1 pulls off some clever tricks, such as a 27-hp electric motor packaged between the pint-sized 48-hp diesel displacing a mere 0.8L and a magnesium 7-speed dual-clutch transmission, all wedged between the driven rear wheels.

Piloting the XL1 is like judging a science project: It feels and sounds strange, and even the locals here, who surely see far-out concepts on a regular basis, stop and stare.

But ultimately the XL1 is disappointing from the driver’s seat for being too bizarre.

For instance, braking is extremely disruptive, especially early on while the ceramic discs remain cold. The first braking event after starting the car triggers what sounds like a tsunami of water rushing through the chassis from the back of the vehicle to the front. Imagine 10 rain sticks riding shotgun when stopping.

VW insists the issue is less noticeable as the brakes heat up. We drove for 45 minutes, and the whooshing sound remained.

Crank windows and manual steering are nostalgic and fun, to a point. Then they become quirky and impractical. But the mission was to strip out every possible gram from inside the XL1. For example, electric power steering would have required a motor and gears that would have added 22 lbs. (10 kg).

The polycarbonate side windows are in two pieces – one fixed along the upper door trim and the other raised and lowered by the hand crank. Separating the two is a piece of trim that runs parallel to the roofline. Problem is, that trim rests at eye level, forcing the driver to crane his neck to see above or below it.

Everything that could be sacrificed to save weight was ditched, including a fair amount of sound damping, clearly, as well as all three mirrors, replaced by side-view cameras feeding images to monitors stationed below the A-pillar on both doors.

Did we mention the air conditioning provides little relief on a sweltering day?

The powertrain propels this low-slung coupe quite nicely, with a top speed of 159 km/h (99 mph), but this plug-in hybrid is geared for fuel efficiency.

With its 5.5 kWh lithium-ion battery fully charged (it takes two hours with a 220V dock), the XL1 can run for 50 km (31 miles) on electricity, alone, then another 449 km (279 miles) on diesel.

That’s similar to a (much heavier) Chevrolet Volt, which has been on the market for three years, seats four, sounds and feels like a normal car and can be leased for less than $300 per month.

VW bills the XL1 as capable of 1.1 L/100 km (261 mpg) based on the European driving cycle, and the carbon-dioxide emission rating of 21 g/km is remarkable.

But that type of efficiency will be elusive whenever the driving range requires the engine to run. In those instances, as with the Volt, the XL1 merely becomes a really expensive compact car.

At the end of our test drive – most of it in electric mode – the trip computer says the XL1 managed 147 mpg (1.6 L/100 km).

VW deserves kudos for pulling off the XL1, and the next iteration is bound to be even better. Perhaps the car’s best attribute is its offset seating, which allows two average-size adults to share an unusually narrow cabin. Plus, there’s no airbag in front of the passenger (another weight savings) because he sits far enough away from the dashboard.

Perhaps our drive impressions have something to do with the chosen routes: The XL1 was driven in and around Wolfsburg during the afternoon rush hour, so there was no open-road cruising.

The Golf GTD was experienced on the autobahn here from Berlin, a gloriously smooth 231-km (143-mile) adult playground that allows vast stretches to reach the top speed of 230 km/h (143 mph).

The GTD doesn’t struggle to reach this velocity but instead does so with authority, aided and abetted by a supremely tuned chassis (front struts and multilink rear) with active damping that holds the road effortlessly and an electrically actuated “progressive steering” system that tracks with poise and precision.

Who would have thought a car this small could handle extreme motoring with such grace? The faster the GTD goes, the more stable it feels.

With 184 hp and 280 lb.-ft. (380 Nm) of torque, the car accelerates to 100 km/h (62 mph) in 7.5 seconds.

Equally impressive about the 2.0L turbodiesel is its fuel economy rating of 4.1 L/100 km (56 mpg) based on the European driving cycle. The U.S. test cycle would translate that highway efficiency to about 5.6 L/100 km (42 mpg).

After our 96-km (60-mile) leg of the trip from Berlin, the vehicle computer reads 6.6 L/100 km (36 mpg), not bad considering multiple runs at wide-open throttle.

Typical of diesel engines of varying displacements, VW’s new TDI delivers massive torque in any gear and at any speed. Even cruising the autobahn at 193 km/h (120 mph), Wolfsburg’s new compression igniter manages to push the driver deeper into the seatback when the throttle is nudged harder.

Along the way, vibration is scant in the steering wheel, the gear shifter and the seat.

This is a world-class diesel, and its newest features include lighter pistons, two balancer shafts with low-friction bearings, variable valve timing, more boost from the new turbocharger, higher-pressure common-rail direct injection, dual-loop exhaust-gas recirculation and an intercooler incorporated within the intake manifold.

The engine complies with the Euro 6 emissions standard with a host of sensors and an oxides of nitrogen storage catalyst placed upstream from the diesel particulate filter. For Europe, the engine requires no urea-based selective catalytic reduction, but that feature will need to be integrated for a U.S. debut to scrub NOx, VW says.

Even if the GTD never comes to the U.S., a detuned base version of this EA288 will arrive, likely in early 2014 under the hood of the all-new Golf.

VW is leading the charge with diesels for the U.S. In June, the auto maker reports a staggering 24.3% diesel take-rate across the lineup, including 31.3% for the Passat fullsize sedan.

This growth has been based on VW’s previous-generation 2.0L diesel, so expect this momentum to continue building. The engine would be more than adequate to power most of the brand’s lineup, including the Jetta, Beetle, Tiguan, Passat and even the new cross/utility vehicle derived from the CrossBlue concept.

In Europe, VW expects the GTD to make up about 10% of Golf sales.

True, the Golf GTD and XL1 are not intended to ply the same market segments, and few people will ever drive an XL1.

But it’s fair to consider these two vehicles blood brothers bound by performance attributes and fuel efficiency that stems directly from VW’s vast expertise in the diesel engine.