Despite the brand's long history in motorsports, Porsche's relationship with Grand Prix racing has been full of fits and starts. The 718RSK originally competed in Formula 2 before moving to Formula 1 in 1961, where the slightly elderly car didn't prove competitive. The 804 got the brand its sole championship race victory as a constructor with Dan Gurney at the wheel in 1962.
From there things stayed quiet for nearly two decades. Porsche focused on sports and GT racing, and ignored the world of open wheel cars entirely. Porsche returned in 1983 as an engine builder in partnership with TAG, and powered two constructor and three driver championships in the mid-1980s. With the rule changes of the early 1990s, the brand appeared very briefly in 1991 with an overweight V12, and failed to even qualify for more than half the races in 1991.
Where Porsche left top-tier endurance racing at the top of the heap and on their own terms, they left F1 in 1991 with their tail between their legs. While Porsche recently announced their return to (more-or-less) open-wheel racing with Formula E, the all-electric championship wasn't their only prospective race series. According to Motorsport.com's interview with Fritz Enzinger, plans were in the works for a Porsche Formula 1 entry:
“In 2017 there were signals from Formula 1 that the regulations were to be changed and that energy recovery from the exhaust gases [the MGU-H] was no longer required,” [Enzinger] said.
“As of 2017, Porsche was a member of the FIA Manufacturers Commission and was involved in the discussions about the future drive strategy in Formula 1 from 2021 and represented at the meetings.
“On the one hand we took part in these working groups. On the other hand the guys developed a six-cylinder for the WEC in parallel. Of course, we thought about what would have to change if the engine were to be used in Formula 1. Such things can be done in two ways.”
Though a move to FE, where Audi was also present, was an "obvious idea", Enzinger said the six-cylinder engine concept was still pursued because an F1 engine without the MGU-H would "also be interesting for a super sports car".
"At the end of 2017, we received a concrete order from our parent company to further develop a highly efficient six-cylinder engine, despite its LMP1 withdrawal," he said.
"Not only on paper, but actually as hardware and with the idea that this engine will be put to the test in 2019. That was the order from the board to us."
Enzinger said its six-cylinder engine "is complete and running on the test bench" as a team of "20 to 25 technicians" use it "for analyses and further orders with regard to series relevance."
Porsche's entry was set to coincide with a 2021 rule change for the series, though given the recent changes in Formula 1, Porsche's future entry in top-tier Grand Prix racing seems to be somewhere between unlikely and impossible.