Porsche conquers the turbocharging world
Blood Alley, 3 a.m. At the tail end of the witching hours, after the wicked have stumbled home to sleep off the evening’s debauchery and before the virtuous rise to greet the day, these streets are empty. There’s no one around but the ghosts of the past.
Handy, then, that we’re here in a Porsche 911 Turbo the exact colours of the Ghostbusters Cadillac: Ecto-III, reporting for duty. It’s haunted, this place. Once, butchers sluiced down the cobblestones with brimming buckets, washing away the carnage of their profession in long, red streaks. Wander about after dark in those days and you might find your own throat cut — robbers and highwaymen once lurked here in darkened doorways, predatory and viciously quick with a blade.
Still, any ghostly ne’erdowould have to be pretty dang quick to catch this twin- proton- packed Porsche. Its flat-six engine displaces 3.8 litres and churns out 520 thundering horsepower, while a sevenspeed dual-clutch gearbox and supernaturally omniscient all-wheel drive get the power down. It’s fleeter of foot than Death’s pale steed, so don’t fear the reaper.
In fact, the 911 Turbo is so composed at wrestling the laws of physics into submission, you could say that it has finally hammered a stake into the last of the demons of turbocharging. No lag. No surge. Nothing but seamless power and acceleration, easily capable of scampering off the line and straight to the police impound lot in the blink of an eye.
I’ve brought it down here, into the psychically charged heart of Gastown in Vancouver, so that it could face up against the ghost of its 1970s progenitor to see how the bogeymen of turbocharging have been laid to rest. You might not be considering a 911 any time soon, but odds are your next car may be equipped with turbo.
The turbocharger is an ancient device, dreamed up in Switzerland by an engineer named Dr. Alfred Buchi in 1905. In essence, it’s brutesimple: while the exhaust coming out of your tailpipe doesn’t appear to have a lot of punch, when it exits the cylinder after ignition, it has the heat and power of a dragon’s sneeze. Buchi hit upon the idea of placing a turbine in this exhaust stream, and then using the harnessed energy to drive a fan ramming air into the cylinder.
More air means more oxygen means more power, assuming you’ve amped up your fuel input to match. Thus, it’s possible to get bigengine output from smallengine displacement, and you’re making power from energy that would only be lost out the back anyway.
When the first 911 Turbo came along in 1975, they called it the Widowmaker. Rear-drive only, and with that flat-six hanging way out beyond the back axle, the first 911 Turbo — known as the 930 — delighted in switching ends under throttle, spinning into the ditch and ferrying its driver off into the afterlife. Exercising demons Over the years, there were several demons for Porsche to exorcise. First, it had to handle the heat. Pressurizing air naturally induces some heat into the mix — think of a bicycle pump — and the packaging requirements of a turbocharger usually mean that the intake air has to pass very close to the exhaust piping. That makes things extra hot, robbing power.
Porsche’s solution to the problem was intercooling. Porsche certainly didn’t invent the idea of cooling down intake air after pressurization, as the technique had been used in supercharged cars as far back as the 1920s, but Porsche did manage to take the knowledge it had gleaned from its mighty turbocharged racing cars and apply it to a road car. Power jumped beyond 300 horsepower, excellent for the time, but the issue of lag still remained.
Where the 930 and other early turbocharged cars were concerned, the delay between stomping on the gofast pedal and actually going fast was interminable. It’s all well and good to be harnessing exhaust gases to make more power, but if the turbine isn’t spinning, then you’re not going anywhere.
The simplest way to deal with the issue is to get a smaller fan. As the impeller side of a turbocharger spins a hundred times faster than an engine, size and weight are extremely important — think how badly a pennyfarthing would do off the line in a cycling sprint race.
Porsche simply divided and conquered. Where once the 930 had been force-fed by a large single compressor, the 959 supercar used two turbos, one large and one small. The smaller turbo helped with off-the-line performance, while the larger turbo came on strong at the top end.
Sequential turbocharging became quite popular in the 1990s, especially in some of the high-tech Japanese sports cars, but Porsche soon turned back to a simpler arrangement. From 1995 until the current car, the 911 would have two smaller identical turbos working in parallel harness.
Porsche also introduced another lag-reducing idea into the 2006 version of its 911 Turbo. Known as variable turbine geometry, this innovation had earlier shown up in a Carroll Shelby-tuned Dodge Shadow, of all things.
Electrically controlled vanes can be shifted to direct the flow of the exhaust gases to the turbine with maximum efficiency. Basically, at low engine speeds, you want the exhaust flow to be squeezed at the turbine, and once the RPMs come up, you expand the opening so that maximum power can flow.
You’ll only really find variable turbine geometry on the 911 Turbo and nowhere else, but a similar effect can be found in other cars with the adoption of twin-scroll turbos. These are designed to harness the exhaust pulses of the cylinders in pairs, so as to reduce lag — think of it as a don’tcross-the-streams type of situation.
The final spectre hanging over any turbocharged car used to be a terrible thirst for premium fuel. Squeezing extra power into a cylinder is great, but it does increase the odds that you’re going to get spontaneous combustion, rather than a smoothly controlled burn radiating out from the sparkplug. Thus, the requirement for higher octane fuel, which burns more slowly, and is resistant to compression ignition.
Drive this latest generation of 911 Turbo on the highway, and it’ll get fuel economy figures not far off a Honda Civic. Sure, some of that’s down to the aerodynamics of the car, but the rest is thanks to the car’s new direct-injection engine.