► Gavin Green takes on turbos
► Natural aspiration more fun
► Drive for efficiency ruining cars?
Back in the hedonistic ’80s, turbos were all the rage. Untrammelled power was, after all, part of the zeitgeist.
Auto makers jumped on the bandwagon and cars so powered typically had ‘Turbo’ advertised large down flank or tail. We even had ‘Turbo’ branded aftershave and trainers for men who wanted to supercharge their lifestyles by, presumably, becoming more fragrant of face or fleet of foot.
When turbochargers first came into vogue – Porsche, BMW and Saab were all pioneers – they were an inexpensive way to boost the power and performance of existing engines. It was easier to bolt on a blower than engineer a new straight-six or V12. Low-cost turbos were a reason for the hot-hatch revolution of the ’80s. The Renault 5 Turbo accelerated almost like a Ferrari yet was priced like a Ford, never mind that when the turbo kicked in the front wheels would tug like a mastiff pulling on the leash.
Those early turbochargers were crude. They were either ‘on’ or ‘off’, with few shades between. They gushed like a broken water main or trickled like a dripping tap when you wanted a precisely controlled flow. This unpredictability of delivery is one reason why many early 911 Turbos wagged their tails, energised by all that untamed turbo torque, before exiting ungraciously into nearby trees.
Only when used in diesels were turbos universally good news. This is no accident. The Swiss engineer Alfred Büchi (in 1909) invented the turbocharger specifically to give more verve to the dowdy diesel. Now turbochargers are enjoying their second coming for petrol cars. They blossom not because they offer superior performance or a more finely honed driving experience. Rather, emission regulations make them the easy answer. If you wish to maintain performance, as buyers demand, but improve fuel economy, as legislators mandate, the simple solution is a smaller capacity turbo engine.
The vast majority of new performance cars now on sale have turbochargers. All new BMW petrol engines are now turbocharged. And BMW was once the world’s most proficient maker of naturally aspirated motors. Despite the newfound dominance of turbo cars, only four of the 11 cars featured in CAR's 2013 Sports Car Giant Test were turbocharged. The winner and runner-up were both naturally aspirated. My personal favourite – the Cayman S, admired for its value as well as its invigorating driving experience – also breathes normally.
I believe this is significant if not surprising. Despite many brave words to the contrary from makers who tread the turbo path, turbocharged motors never offer the same rich driving experience as a good naturally aspirated engine. They can offer as much – or more – power and they can thrill as extravagantly. Their great gust of high explosive power can be intoxicating. But they never offer that progressive linearity, or the throttle sensitivity, that good naturally aspirated engines serve up in carefully incremental doses. Unlike turbos, engines that breathe normally deliver rush without gush.
Pilot the Ferrari F12 (or even better, a 458) or the Porsche GT3 or the Cayman or any good non-turbo 911, and that delicious throttle response means you can enjoy an instant crack of power that’s just a toe twitch away. Mid-corner, you can steer the car with the throttle as much as the steering wheel. There is no lag between instruction and action. A delicate throttle doesn’t just make a car go and slow; it makes it a lively, animate companion always at your immediate command. Plus, a good naturally aspirated engine invariably sounds better, more mechanical growl and snarl than turbine whirr and bellow.
What is the definition of a great performance car? It is not top speed, or 0-60, or those absurd Nurburgring lap times about which too many makers fret. What’s important is transient performance – acceleration, braking, changing direction and, more than anything, instant throttle response. It’s agility mixed with muscle.
This is why the Bugatti Veyron fails as a sports car. It may have 1000bhp and do 250mph. But the throttle lag makes that irrelevant. It is why the marvellous McLaren 12C Spider, the best turbo car of our 11 finalists, would be even better with a Ferrari 458 engine (or the McLaren F1’s old BMW V12) wailing in its tail.
Of course, the turbo rush is mostly about improving fuel economy, the only data that matters to the motor industry. Real world mpg is almost irrelevant. Yet when driven half-energetically a turbo can guzzle gas as fast as a big capacity naturally aspirated motor, often more. It’s just another example of how ‘official’ fuel figure obsession is changing the motoring landscape, and not always for the better.