Image Credit: RM Sotheby's.The Ferrari F40 is already one of the most desirable supercars ever built. Few examples, however, have a story as compelling as the car now heading to auction through RM Sotheby's.This 1990 Ferrari F40 is known as the "Jean Sage" car, named after the French motorsport figure who originally owned it. Sage was deeply connected to Ferrari competition programs, giving this car a level of provenance most F40s cannot match.The car was later modified by Michelotto, the Italian specialist closely associated with Ferrari's racing projects. Those upgrades turned it into a lighter, more powerful, road-legal machine inspired by F40 competition development.AdvertisementAdvertisementRM Sotheby's estimates the car will sell for between £2.7 million and £3.2 million. Given its history, specification, and documentation, it could become one of the most closely watched F40 sales of the year.A Special F40 From the StartImage Credit: RM Sotheby's.Chassis 84642 was supplied new through Ferrari's French distributor Charles Pozzi to Jean Sage. It is also a desirable "non-cat, non-adjust" example, which is widely regarded as the purest version of the F40, making it especially attractive to collectors. Basically, it's lighter, more powerful, and more mechanically simple than the later versions with catalytic converters and adjustable suspension, making it closer to Enzo Ferrari's original vision of the F40 as a raw, uncompromising driver's car.It should also be noted that Sage was not a casual Ferrari owner. He had managed Renault's early Formula 1 efforts and later joined Ferrari France, where he helped oversee the F40 IMSA program in the United States.Michelotto Turned It Into a Road-Legal WeaponImage Credit: RM Sotheby's.In 1994, Sage sent the car to Michelotto for a series of upgrades inspired by CSAI GT specification. The goal was to sharpen the F40's performance while keeping it usable on the road.AdvertisementAdvertisementMichelotto rebuilt the original engine with special IHI turbochargers and fitted a lightweight exhaust system. Output rose to 527 horsepower, while torque increased dramatically to 626 pound-feet.The upgrades went well beyond power. Michelotto fitted lighter front and rear clamshells, sliding windows, carbon-fiber bucket seats, revised suspension, upgraded brakes, and OZ Racing 17-inch monoblock wheels.Serious Weight Savings and Track CredibilityImage Credit: RM Sotheby's.The changes reportedly removed 136 kilograms from the car. That made this F40 lighter than a standard model while also giving it more power.Its competition credentials were not theoretical. In 1995, the car took part in qualifying for the BPR Global Endurance GT Championship at Paul Ricard and posted the quickest time in its GT4 category.AdvertisementAdvertisementIt also finished only six seconds slower than a full F40 LM entered at the same event. For a road-legal F40, that performance remains seriously impressive.Documentation Adds to the AppealThe car still retains its matching-numbers engine and gearbox. At the time of cataloguing, it showed 22,699 kilometers, or roughly 14,105 miles.It is accompanied by its Schedoni leather folio, original service and warranty book, Massini report, maintenance invoices, and MoT certificates dating back to 2003. Recent work includes new fuel tanks, cambelts, spark plugs, fuel filter, and an engine oil service.A Rare Chance at an Exceptional F40Plenty of Ferrari F40s are valuable, but this example combines road legality, Michelotto engineering, motorsport links, and major-name ownership. That combination places it in a very small group of collector-grade F40s.AdvertisementAdvertisementSage's personal connection to Ferrari competition makes the car especially compelling. For collectors chasing an F40 with both performance and provenance, chassis 84642 may be one of the strongest examples to reach the market in years.If you want more stories like this, follow Guessing Headlights on Yahoo so you don't miss what's coming next.