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05 – Espace technique

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The History and Operation of Porsche Rear-Wheel Steering

While four-wheel steering wasn’t uncommon twenty-five years ago in the heyday of tech-heavy sports cars, we seem to have left some of those gizmos behind with the implied understanding that they were superfluous. Yet, with lengthening wheelbases in the current Porsche lineup and more and more weight, it’s become a useful tool to make the latest fleet of Porsches rotate accurately, easily, and predictably.

If we’re to trace the history of Porsche’s rear-wheel steering back to its inception, we find the first system was used in the innovative 928. Its passive rear-wheel steering system, also known as the Weissach axle, was a means of mitigating lift-off oversteer—the tendency which made the 911 such a feared car in the sixties, seventies, and early eighties. While the semi-trailing arm rear suspension used with these early 911s was cost-effective and quiet in operation, it had a tendency to try and pull away from the Porsche’s body during deceleration; the elasticity in the rubber bushings causing toe-out and the resulting instability.

Photo credit: Motor-car.net

With the Weissach axle, the front pivot bushing of the trailing arm was replaced by a short link, and the innermost mount was moved rearward. Additionally, a third, pivoted linkage sat between the front-most mount and the upright. This design caused the wheel to pull toward the car under deceleration; resulting in stable, reassuring toe-in. This passive system was the furthest Porsche took the rear-wheel steering idea until recently, though an electrically-controlled active system was tested in the 993 before it was shelved due to complexity.

Moving Forward Thirty Years

The current rear-wheel steering systems available on the Carrera S, GT3, and Turbo are much more sophisticated and adapt to conditions to provide different outcomes, but their operation principles are simple. At low speeds, where agility takes precedence, the rear wheels move in the opposite direction of the fronts. This shortens the curve the car must take and helps navigating parking lots or hairpins. That rotation also helps mitigate some of the potential for understeer; a trait that plagues 911s, especially with the longer wheelbase of the 991.

Up to 31 miles an hour, the rear steering effectively shortens the wheelbase by nearly 16 inches. The full 2.8 degrees of rear steering in this situation equates to something like 45 degrees of steering lock.

At higher speeds, stability is the aim. Above 50 miles an hour, the rears begin to steer in-line (as much as 1.5 degrees) with the fronts, effectively lengthening the wheelbase by up to 19 inches. Between 31 and 50 miles an hour, the computer determines the ideal course of action according to road speed, steering angle, and longitudinal and latitudinal acceleration. Additionally, the rears straighten in the event the driver is purposefully causing the car to oversteer. Clever stuff.

The steering arms are either pushed or pulled by actuators located just ahead of the top wishbone, the Porsche navigates the corner much more easily, and the driver familiar with the steering effort required in a 996 or a 997 is left flabbergasted at the sheer ease with which the modern breed can corner.

Watch as Chris Harris describes how little steering lock is needed to get the most out of a 991 GT3.

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VIDÉO – Porsche présente les avantages de son moteur boxer

Le nouvel épisode des Porsche Top 5 Series met le fameux « boxer » à l’honneur.

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How Does The Turbocharger In Your Porsche Work?

If you’re a Porsche fanatic, chances are pretty great that some of your favorite cars from the brand’s history are turbocharged. A lot of their greatest hits are powered by engines with exhaust-driven forced induction. Not only was Porsche a pioneer in turbocharged race cars, but they were among the first companies to sell a turbocharged street car as well. To this day, turbocharging remains quite important to the company, as the majority of their cars on the dealer showroom are turbocharged. With the exception of the GT3 and GT3 RS, Porsche does not currently make any naturally aspirated cars, every 718, 911, Cayenne, Macan, and Panamera is turbocharged. So, if you’ve ever wanted to know how the turbocharger (or turbochargers) under your hood (or decklid) work, this new video from Donut Media is for you.

This is an entertaining view of the inner workings of the turbocharger, specifically angled at the layperson. It’s not overly complicated or difficult to understand if you have a modicum of mechanical knowledge. There is, of course, a lot more information than can be conveyed in a 7-minute video, but it’s an excellent place to start.

Porsche’s Turbo History Milestones

Technically, it was General Motors who introduced the automotive world to turbocharging with the Oldsmobile Cutlass JetFire in 1962. Turbos had been used in aeronautical applications for years to help engine power correct for altitude. The technology wasn’t quite ready for prime time in cars, and GM shelved the project for a few more years. Porsche picked up the torch, and they’ve been running with it ever since.

The Can Am 917

Porsche, using the crucible of motorsport to develop this brand new tech, started working on a high-powered 917 engine for Can Am in the early 1970s, and rolled it out in full force for the 1972 season, a full decade after the JetFire engine launched. While their 917 already had a huge flat-12 engine that had dominated at Le Mans, it wasn’t nearly enough power to take the fight to McLaren’s big-block V8s in the North American prototype series. The 917/10 was born, and it was immediately dominant at the hands of Penske Racing.

The First Turbocharged 911 Racer

The car pictured below, Porsche’s 1974 911 Carrera RSR 2.1L Turbo, was campaigned by the Porsche factory in international sports car racing, and paved the way for a street-going counterpart. This exact car raced its way to second overall at Le Mans and Watkins Glen in 1974. It was incredibly fast, having been alleged to produce over 500 horsepower from its relatively small engine.

The First 930

The very first 911 Turbo, seen below, was a gift to Louise Piech in 1973. The car was built effectively from a Carrera 3.0L basis, and fitted with a more powerful turbocharged engine. This same basic design was later adapted for production use and sold in showrooms as early as 1975 in Europe. It was capable of a 5.5-second 0-60 sprint and a top speed of over 155 miles per hour, making it one of the quickest and fastest production cars of all time up to that point.

The Inimitable 959

After Porsche had proved twin-turbocharging could be made possible with the 917/30 and later 956/962 variants, they took things to a brand new level in production supercars with the launch of the 959. While those earlier twin-turbocharged cars used two parallel turbochargers to reduce turbo lag and split each half of the engine into its own turbocharger, the 959 introduced sequential twin turbos. Unlike parallel twins, where each turbo works independently, and boost pressure builds at the same engine speed, a sequentially activated turbo setup features one small turbo, which spools at lower RPMs, and the other is a larger turbo which builds more pressure but operates at higher engine RPMs.

Since then, Porsche has continued to develop new turbo technology, more or less at the forefront of advancement. They’ve worked to pioneer things like variable geometry turbines that work effectively like a pair of sequential turbos, but held within the same housing. They’ve produced electrically-assisted turbochargers to reduce lag in their 919 Hybrid LMP1 racer. It’s a whole new world at Porsche right now, and turbo technology is still at the forefront like it has been for nearly fifty years.

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Porsche : le moteur « boxer » expliqué

VIDEO. Porsche présente les cinq principaux avantages de son moteur « boxer ».

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Inside the Boxer Engine with Hans Mezger

Hans Mezger is 88 years old, and his career designing engines spans decades. Mezger’s hands were in everything from the 1960’s Porsche Formula 1 racers to the 911 GT1. His engines remained in 911s through the 997 GT3 4.0 and 997.1 Turbo. It really feels as though everything Porsche produced since is compared to the Mezger flat-sixes. This family of engines defined Porsche drivetrains for decades. While Porsche used boxer engines prior to his arrival with the company, his influence elevated Porsche beyond its Volkswagen roots. Jean Pierre Kraemer of JP Performance and Herr Mezger, together, probably know more about flat-sixes than anyone on Earth. Who better to take us through the heart of a Porsche?

Very few brands are defined by their use of a horizontally opposed engine. Volkswagen has long since abandoned the format, Franklin has been gone since the Great Depression, and many others have fallen by the wayside. In the US market, just Porsche and Subaru remain standing with a boxer engine. Thanks to their low center of gravity and clever management of internal masses, Porsche engines can be powerful and refined, while allowing the car to handle in a stable way.

Mezger’s modesty and JP’s enthusiasm mesh well, and demonstrate the dichotomy of Porsche. On one hand, we have a quiet, clinical perfectionist explaining what it takes to make the car work in the first place. On the other a rabid enthusiast. According to Mezger, his design work was best done at home, when things were quiet and his wife left him to his work.

Despite his age, the era of Mezger is still not over. He is working with Singer and Williams to create a 9,000 rpm, 24-valve screamer for the latest Singer projects.

Of course, while I could go off at some length about why boxer engines are wonderful and why LS-swapped 911s fly in the face of basic decency, I don’t have to. Herr Mezger is here to do just that.

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