Heart of the matter

JOHN CAREY

Andreas Preuninger, Porsche’s director of high-performance cars and motorsport, knows the engine of the 991 GT3 RS inside out. At the car’s launch last year he listed for Wheels the alterations that set it apart from the naturally aspirated 3.8-litre version of the company’s 9A1 flat-six family.

“We’ve got different pistons, different crankcase, different bearings,” he said. “The machining of the cylinder block is completely different to enable the 4.0-litre displacement. The heads are completely different, the valves are lighter, the valvetrain is different, the exhaust is different.”

The crankshaft is made from the same stuff as in the 919 Hybrid LMP1 racer – tempered steel remelted multiple times in a vacuum to produce a part of exceptional purity and strength. It increases stroke by 4mm over the 3.8-litre. The dry-sumped engine has titanium connecting rods and an induction system that utilises the rear guards’ intercooler air intakes from the 911 Turbo to instead provide ram-air effect for the naturally aspirated engine.

“It’s a new engine,” Preuninger concludes. It’s hard to argue.

Maybe it would be easier to say what the GT3 RS engine does share with the 3.8-litre? Preuninger thinks. “The chains for the valvetrain, the bolts for the cylinder heads, the compressor for the A/C… It’s really nothing much.”

Porsche’s very nearly all-new 4.0-litre marks the end of the famed ‘Mezger Block’ series of GT3 engines, named after legendary Porsche engineer Hans Mezger, who retired in 1994. This is the last of the line. Yet despite its newness, the engine of the 991 GT3 RS only matches the power output of its same-size 997 predecessor…