It was at the 1973 Frankfurt auto show where Porsche first made it publicly known that it was working on a new high-powered 911. The car would be equipped with a turbocharged flat-6. It would eventually become the 930-generation 911 Turbo.

The announcement was made with the reveal of a concept, shown here following a restoration by its current owner to bring it back to its condition at its Frankfurt debut.

The car Porsche presented all those years ago didn’t actually have a working turbocharged engine. Due to delays in development, the automaker installed a naturally aspirated engine with a mock turbocharging system made from wood and painted to look like metal. The car was the first 911 to wear a “Turbo” script, though, in this case as a hand-painted graphic on its flanks.

It was based on a 1973 911 S, chassis number 9113300157, but given the wider body of the later production 911 Turbo, a huge rear wing, and larger-diameter Fuchs-style wheels.

The concept would later be presented at a few additional shows and eventually used as a development mule for race car parts after production of the 911 Turbo got underway in 1974. It then entered private hands in 1975 when Alan Hamilton, a racing driver and Porsche’s importer for Australia, spotted the car during a Porsche factory visit and negotiated buying it.

The car has since traded hands several times and currently resides in Europe. It’s scheduled to make a public appearance at an event at Hampton Court Palace in the U.K. starting Aug. 30.

It isn’t considered to be the first 911 Turbo. That honor goes to a separate narrow-body car devoid of any “Turbo” markings but equipped with the 2.7-liter turbocharged flat-6, which was delivered to Louise Piëch, a daughter of Porsche founder Ferdinand Porsche, on her 70th birthday. That was also in 1973, albeit prior to that year’s Frankfurt auto show. That car is now in the Porsche Museum in Stuttgart.