Alpina, Audi, Alfa Romeo and BMW take on the 150mph/50mpg challenge

Perhaps. But because it remains to be seen what the car in question even looks like, best to throw the net pretty wide and use instinct to decide if it’s catching cars that have a real chance. Pick overly powerful machinery to succeed on the acceleration tests and you’ll compromise your economy result. Err too much on the side of caution and you won’t pick a 150mph standing-mile car at all.

That’s how we ended up with a mix of saloon, estate and sports car bodystyles on the starting blocks here, and petrol and diesel power (both turbocharged) and a petrol-electric hybrid. Welcome, then, the state-of-the-art BMW i8 plug-in hybrid, the formidable and multi-talented Alpina D3 Biturbo Touring, the brand-new Audi A4 3.0 TDI and the lightweight Alfa Romeo 4C Spider.

All four cars have claimed top speeds of more than 150mph. All four have New European Driving Cycle extra-urban fuel economy claims (for what they’re worth) that top 50mpg, with three out of four beating that marker on the NEDC combined figure as well. Any one of them could be our 150mph and 50mpg landmark. Or all of them could.

Standard operating procedure means that all four cars start the comparison with a full tank of fuel but, with a plug-in hybrid in the mix, ensuring a level playing field is necessarily a bit more complicated than that.

The i8’s high-voltage electrical system could queer our pitch on both performance and economy. The car has a zero-emissions range of more than the 12 miles it takes to complete the touring test, and more than 100bhp of electrical boost that only works when there’s charge in the batteries. But we need to be fair to it, as well as to everything else.

So the i8 gets access to every available bit of grunt for the acceleration runs, but we’ll make it run on petrol power alone – as it might on a long touring run – for the economy testing.

Acceleration tests first. They’re more exciting, more hazardous and, with the weather starting fairly dry and threatening to get worse, more adversely affected by rain. MIRA’s mile straights are among its newest facilities, so their surface is perfectly smooth. They’re two lanes wide for most of their length, narrowing to 
a single banked lane at either end that feeds around to return you to the beginning of the opposite leg to the one you’ve just come down.

Life on the mile straights can get interesting when you go through the mile marker flat out at more than 150mph, because there’s only about 300 yards after the mile marker in which to slow the car for the banking – which you’ll most likely career off if you attempt to carry much more than 50mph.

Touch wood, I’ve never done a Beauregard Duke impression off the high side of either of the return loops, but I’ve certainly had my moments under braking. Locked wheels in slippery conditions in cars on cold tyres and with no ABS, chiefly. I once had a brush with one of rural Nuneaton’s many pheasants. Evidently, you don’t need a security pass to get into the place if you’re a Mongolian ring-neck.

With a sneaky suspicion that peak power will be telling, we’ll start in the least powerful, least promising car of the bunch: the 4C Spider. It’s an outside bet to crack our two surveyed objectives, sure, but not out of the question. It’s light, aerodynamic and grippy enough to put its 237bhp down, but not so over-endowed with tyre footprint as to adversely affect rolling resistance. It has a modern downsized turbo petrol engine and an efficient twin-clutch gearbox, too. And launch control.

The four-cylinder engine’s response feels a bit soft under your right foot, but launch control keeps it spinning industriously until you lift your foot off the unusual floor-hinged brake pedal and engage drive – at which point the 4C takes off with plenty of vim and vigour. Keep your eye on the rev counter, because the redline is set only just above 6000rpm and, despite the tailing off of the torque delivery, it’s easy to hit. If in doubt, tug that right-hand paddle for the next ratio.

The car sprints to 60mph in 5.1sec and to 100mph in 12.4sec. Not bad. As we’ll find out, only one car here will go faster over those trips. But the 4C doesn’t hit 150mph, with drag taking a heavy toll on its rate of acceleration above 100mph. Terminal speed is pegged at 141.4mph. A steady start.

Next, the A4 3.0 TDI quattro, a car whose all-paw drivetrain gives it about as much need of a launch control system as it might have of a diamond-encrusted dead man’s pedal. This full-house 268bhp version combines that engine and four-wheel drive system with an eight-speed torque-converter automatic gearbox, whereas less powerful versions come with a twin-clutch equivalent. But still, freshness to market, combined with Audi’s typical focus on efficiency, means that like-for-like executive saloons don’t come much more frugal.

There’s no need to worry about shifting gears here – just wind up the torque converter against the brake pedal and then mash the accelerator pedal. The car rumbles swiftly and smoothly through its lower ratios but, save for a fairly savage release from rest, it never feels desperately fast. It’s brisk, sure, but less and less so as speed rises. There’s enough time to notice that we’ll be lucky to average less than 15.0sec to 100mph. Eking out as much speed as possible before braking, the car averages a top speed of 136mph.

Time to get serious. I’d have put my next pay rise on the D3 Biturbo striking the sweetest compromise here of performance and economy, having seen upwards of 50mpg from six-cylinder BMW diesels on several occasions on the road and already sampled the latest Alpina version’s punchy turn of speed first hand. But we’ve got the rear-wheel-drive version of the car and conditions are just greasy enough to make it struggle for grip ever so slightly, even with launch control.

Once third gear is in train, the car forges on as if our chilly winter day was in fact bone dry and 30deg C, its motor revving so freely that you wouldn’t believe it could be diesel. Having missed Alpina’s 4.6sec claim to 62mph by quite a way, the D3 dips under 13.0sec to 100mph. More like it.

It feels like it’d run well beyond 150mph given enough room but, disappointingly, not here and now. The end of the straights calls time on the D3’s top speed at a two-way average of 144mph.

With only one car left, my worry is that nothing will crack the 150mph standing-mile threshold, bringing our test to a premature end. But we’ve saved the carbonfibre-tubbed wild card until last: the i8, the most accelerative car here, according to those manufacturer claims. Not that it’s an easy car to set into motion with optimal force.

BMW does include a launch control mode, but it doesn’t seem to work well with the car’s electric motors, so holding the car on both pedals feels a bit like you’re inadvertently tearing it in two.

Be quick in the transition between throttle and brake and all is well, though. Very well. Beating the next quickest car here by 0.4sec to 60mph is one thing. Pulling out a 1.5sec advantage by 100mph is quite another. This is what proper sports car pace feels like and the terminal standing-mile speed is 151mph. Hallelujah – we have a contender.

And there being only one car in with a shout of setting our double-whammy landmark by the time the economy testing comes around also neatly simplifies our denouement. For the record, all four cars did the three flying 60mph laps of the MIRA ‘number one’ circuit required for an official touring test result. All four produced economy numbers via trip computer, whose accuracy was subsequently calibrated between tank-to-tank fills. And the results (see below) may very well surprise you. They certainly did me.

The most economical car here at a steady 60mph? Take a bow, the 4C Spider, not only surprisingly parsimonious but also modest with it, since it was the only car on test whose trip computer underestimated its real-world economy. The next time you assume a modern sports car won’t be modern enough to be genuinely frugal, think again.

For a while, the Audi looked like it might at least record an indicated 50mpg, but its trip computer turned out to be dismayingly optimistic. The Alpina never really approached our hoped-for economy standard, although a 42.5mpg return from what, I’m sure, would have been a sub-5.0sec-to-60mph super-estate on a dryer, warmer day is certainly no mean achievement.

Only one question remains, 
then: is the i8 Autocar’s first 
150mph and 50mpg landmark? Afraid not. A 42.4mpg touring test return, corrected to 41.0mpg after trip computer calibration, leaves it pretty smoky in terms of bald speed but, in this instance, wanting its victory cigar.

So the wait goes on. And I 
wonder how many more Autocar 
road testers it’ll outlast. 

The results are in...

0-60mph: BMW i8 4.7sec, Apina D3 Birturbo Touring 5.4sec, Audi A4 3.0 TDI 5.6sec, Alfa Romeo 4C Spider 5.1sec