The Six-Second Advantage

Also from Issue 197

  • Michael Mauer on the 991
  • 1950 356 cabriolet
  • 1984 911 Carrera Targa
  • Falken's change of pace
  • 1994 911 RS America
  • 1978 928: A lovely old shed
  • Project 914 3.6 — Part 18.5
  • Slave and master cylinder
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While the GT3 RS 4.0 uses a chassis that’s largely the same as the RS 3.8’s, it is an evolution twice removed. Just as lessons learned from the GT3 RS 3.8 suspension development program were applied to the twin-turbocharged, 620-hp GT2 RS, lessons learned from the GT2 RS program have been applied to the RS 4.0.

“The turbocharged GT2 RS is heavier at the rear, so the springs and dampers are different,” says Preuninger. “The main and helper springs for this car are painted yellow, with red ones for the normally-aspirated GT3 RS 3.8 and 4.0.” The rates on the RS 4.0 are higher than those on the 3.8, but lower than those on the GT2 RS.

“All of the rear suspension lower arms and links are Rose-jointed for sharper and more accurate response,” says Preuninger. “This faster-reacting rear end is closely linked to the improved aerodynamics of the 4.0. Working in partnership, they produce the fine balance we were after."

Beyond the busy 4.0 decal set, the only external differences between RS 3.8 and RS 4.0 are the distinctive dive planes on the sides of the front bumper and the new side plates on the rear wing. But there is another tweak your eyes will struggle to catch: “We increased the rear wing’s angle of attack from 6.8° to 9.0°, and the dive planes in front balance this out,” explains Preuninger. “We now have 195 kilograms (430 pounds) of total downforce at 310 km/h (193 mph), which makes the car noticeably more stable at high speeds.”

More revealing than the total downforce is how it is distributed across the chassis: 82 pounds up front and 348 at the rear. “This is 10-percent more than the 3.8 at the rear, and proportionately the same as before in front,” says Preuninger. “On the Nürburgring, long, fast corners can now be taken flat out due to the more planted front end. The dive planes are smaller versions of the ones on the RSR. We even tried the race ones, but found that these can make the car feel edgy. The RSR has a larger rear wing to balance things out, but this is too big for road use.

“The improved aerodynamics and the alterations to the elastokinematics of the chassis caused by the Rose-jointing required some fine tuning of the geometry,” says Preuninger. “We increased the negative camber by exactly 0° 05’ on both axles, so the front now has 1° 40’, with 1° 50’ at the rear. In combination with the solid lower bushings and the extra downforce, you can really feel the im­provement in fast bends.”

Due to weight discrepancies encountered in the past between Porsche’s stated curb weights and test cars we’ve put on the scales, we were curious about how Porsche measures its cars. “The dry weight of the RS 4.0 is 1,270 kilograms (2,800 pounds),” says Preuninger. “To that we add 45 kilograms for fuel, 30 kilograms for coolant, 10 kilograms for oil, and five kilograms for windscreen washer fluid. Thus, our official curb weight is 1,360 kilograms (2,998 pounds) — in the lightest specification that a customer can order the car.”

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