The new GT3 rolls on Michelin’s latest Pilot Sport Cup tires, in 235/35ZR19 and 305/30ZR19 sizing. These utilize a new compound, primarily due to new European laws preventing certain chemicals from being used in tire rubber. Says Preuninger: “Performance is pretty much the same as before in the dry, but wet grip is a bit better. With 4.5 millimeters of tread depth when new, wet performance is as good as any normal tire with the same tread depth. Of course, aquaplaning on standing water is the main issue. The driver has to realize that this tire is really focused on dry performance.”
The optional PCCB brake system is the same as the one used in 2008 GT3s, but the standard brakes have taken a significant step. “The old steel brakes used 350-millimeter front discs,” explains Preuninger. “We now use 380-millimeter discs with aluminum hubs located with stainless steel bolts. The weight saving is 600 grams per rotor compared to the old system, even though the discs are larger!”
The new, two-piece rear discs measure 350 mm and also shave 600 grams. While brake cooling is unchanged up front, Porsche fit new components to channel more cooling air to the rear discs. The company says these lowered rear brake temperatures by up to 140º F during intense track testing, with noticeable benefits in pad performance and wear.
The more capable standard brakes reflect changes made in the engine compartment. Weissach had decided that it was time for more cubic inches. Explains Preuninger: “We had reached the end of the road with the 3.6 in two respects. If we further increased power, we would lose tractability and emissions and impact long-term reliability. Secondly, the FIA GT rules had changed in the intervening years. Where we were previously only allowed a 3.6-liter maximum, we can now run up to 4.0 liters as we now do with the RSR. This gives us a lot more freedom to play around with the capacity of the road-legal homologation car. It is in our best interest to take full advantage of that.”
The racing department was consulted, and it viewed 3.8 liters as the optimum displacement for the road car. Says Preuninger: “The 4.0-liter RSR engine uses a different crankshaft, and we decided early on that we did not want to go down that road for a number of reasons. We wanted to retain the proven crankshaft from the 3.6-liter version of the venerable dry-sump GT1 motor because its short stroke gives the engine its free and high-revving nature, something GT3 drivers tell us is vital to the car’s character.”
Changing the 100-mm diameter pistons for 102.7-mm pistons reduces the amount of metal between the cylinders. To compensate for the loss of rigidity in the cylinder blocks, steel liners from the GT3 RSR replace the alloy liners used in the last GT3. The steel liners may carry the same part number as the ones used in the racing RSR, but they add weight — 6.6 pounds of it — to the back of the car.
“We went through a serious weight-paring process in other areas of the engine to compensate for this,” says Preuninger. “We looked at everything from tappets to the dual-mass flywheel, shaving off a gram here and a few more grams there, even using expensive parts like magnesium brackets.” The result is a 3.8-liter engine that’s 3.97 pounds lighter than the 3.6 six it replaces.
The 102.7-mm forged pistons are married to the same titanium connecting rods as before, but the forged steel crankshaft has been shot-peened for extra hardness. The combustion chambers in the cylinder heads are mechanically polished to ensure the compression ratio of 12.0:1 is precise across all six cylinders.