They called the model the “Giant Killer,” and back in the late 1950s, this specific pocket-sized Porsche, with sports-car ace Jack McAfee at the wheel, battled more powerful rivals to dominate Sports Car Club of America (SCCA) racing on tracks across Southern California. Everywhere from Laguna Seca and Riverside to Palm Springs and Santa Barbara, this silver bullet took win after win. Even after changing hands, it raced competitively until 1962.

Now, after more than 60 years of being the pride and joy of collectors around the world, and just out of an exhaustive six-year restoration by Andy Prill, a renowned classic-Porsche specialist in England, this 550A is heading to auction.

“Today, the car is as perfect as the day it came out of the factory, and is ready to take part in any of the great classic events, from the Mille Miglia to the Grand Prix de Monaco Historique to the Monterey Historics,” Harvey Stanley, global director of the Private Sales division of RM Sotheby’s, tells Robb Report. “This car is not only the holy grail of 550A Spyders, but of all vintage Porsches.”

Its appeal is down to that impressive racing history, its known ownership from new, its comprehensive documentation, and the open-checkbook restoration. “This is a hugely significant Porsche, and a key piece of Porsche’s American racing history. And it’s ready to go straight out on to the track, or a road event, and be a joy to drive,” adds Stanley.

While RM Sotheby’s gives a €3.5 million to €3.8 million ($4.05 million to $4.4 million) estimate, Stanley explains the seemingly low price range was included to “open the car up to the market.” When the car was last at auction, at the RM Sotheby’s Monterey sale in 2018, it sold for $4.9 million. And that was before the latest restoration.

In March of 1957, chassis No. 0116 was delivered to Jack McAfee’s Porsche dealership in Burbank, Calif., to replace an RS 550 Spyder. This new 550A model featured a lighter, more rigid spaceframe chassis in place of the original ladder-frame setup. Suspension and brakes were also uprated, as was the 135 hp, 1.5-liter four-cam “boxer” four-cylinder engine. With overall weight shaved to a mere 1,200 pounds, the vehicle, with hand-formed aerodynamic bodywork by Porsche supplier Karosserie Wendler, hits a top speed of nearly 150 mph.

After its racing career, the car spent time with collectors in South Africa before returning to the U.S., where it sold to famed race team owner Dick Barbour, a two-time class winner at the 24 Hours of Le Mans. In 1993, the Porsche was acquired by Japanese collector Hui Takahara and shipped to Germany for a comprehensive restoration by Porsche specialist Freisinger Motorsports.

It returned stateside in 2013, joining the Florida-based Alegra collection, owned by Porsche racer Carlos De Quesada. He showed the car the following year at the Amelia Island Concours d’Elegance, where it was awarded Best in Class. Following the 2018 RM Sotheby’s sale, the 550A was dispatched to Prill Porsche Classics in Essex, England, for the restoration that would involve well over 1,000 hours and cost close to $400,000. It included a full, bare-metal repair and repaint, and a full engine and gearbox rebuild. “This is as close to a brand new 550A Spyder as you can get,” explains Prill. “Apart from an initial test drive, it is “box fresh” and ready to be enjoyed.”

The Porsche restorer explains that the 550A comes with one unique feature that sets it apart from the 39 other examples built. The original RS 550 Spyder featured rear bodywork that could be tilted backwards to make for easier access to the engine. With the arrival of the 550A, that rear body was fixed, with only louvered opening side panels offering access.

Explains Prill: “Early in its racing career, it seems Jack McAfee dented the rear end quite badly. When it was repaired, preferring the opening rear of the original RS 550, he had the 550A’s rear body replaced with an opening section. For our restoration, the owner decided to keep it that way.”

Adding to the car’s collectability is its extensive documentation, period photographs, and race-event programs—even the original driver’s manual. The RM Sotheby’s 77-lot Monaco auction is being held at the principality’s Grimaldi Forum and coincides with the Grand Prix de Monaco Historique race weekend. The auction takes place on Saturday, April 25.

Click here for more photos of this 1957 Porsche 550A Spyder.