The first race was held at Virginia International Raceway; it was an unexpected success, with both the drivers and the handful of spectators who attended.

[5] For the following year, John Bishop brought in sponsor R. J. Reynolds, and in 1975 introduced a new category: All American Grand Touring (AAGT).

IMSA permitted turbocharged cars to compete for the first time, as well as introducing a new category: GTX, based on Group 5 rules.

After a period of multiple ownerships, the organization, by then owned by Don Panoz, was eventually renamed Professional Sports Car Racing (PSCR).

The sponsor's corporate decal had to be displayed and clearly visible on the left and right sides of all racecars, and Camel's corporate logo patch was also required to be on the Nomex driver suit's breast area, featuring Joe Camel smiling and smoking a cigarette while driving a race car.

[7] Initially, all cars were identified with a category tag, stating which category they competed in,[8] but from the middle of the 1975 season on, all cars within the series had to have a rectangular IMSA GT decal, which incorporated its logo on the left, followed by a large GT tag,[9] as well as a Joe Camel decal.

[citation needed] In 1975 a new category, All American Grand Touring (AAGT), was introduced to counteract the Porsche dominance in GTO.

[10] In 1981, the Bob Sharp Racing team used a loophole in the rules to build a Datsun 280ZX inside the U.S. with a V8 engine from a Nissan President.

They were allowed following protests by Porsche's motorsport department, after inspecting Al Holbert's AAGT winning Chevrolet Monza, which had won two titles.

[13] As a result, the new premier class known as GTX (Grand Touring Experimental, which was based on FIA's Group 5), brought on the absolute dominance of the Porsche 935.

[18] One outstanding feature of the car was the 4T-GTE engine, from its Safari Rally-winning, Group B predecessor, producing around 475 hp (354 kW).

[13] Piloted by the likes of Chris Cord, Willy T. Ribbs, and Dennis Aase, the car was dominant in its class right up until the team's move to GTP.

Other teams would follow this example, with notable cars such as the Chevrolet Beretta (in the Trans-Am series) and the Mazda MX-6 (in IMSA GTU).

Otherwise, the cars were required to closely resemble their showroom counterparts, though fenders could be widened, increasing the track up to 79 inches (2,000 mm).

[13] There were no restrictions on body materials, as most teams favored removable, easy to repair fiberglass (meaning one of the only remaining panels from a car's production counterpart was the steel roof structure).

Audi stayed away from the early season endurance classics (Daytona and Sebring), and had two cars drop out of the race in two different rounds,[19] thereby costing them both the manufacturer's and driver's titles, Hans-Joachim Stuck driving.

Toyota was quickest in 1992 and 1993, at the end of the GTP era, as Dan Gurney's All American Racers team campaigned the Eagle Mk III, a car so dominant that it has been blamed for the demise of the class.

[21] Camel Lights cars also used the same decal[22] There were many other manufacturers in the GTP class, such as URD Rennsport, Spice, Intrepid or Gebhardt, and in the early 1990s, Mazda.

Critics predicted that the decreased variety of cars would disappoint race fans, and in fact, it did finally kill the series in 1993.

After skipping the 12 Hours of Sebring, the category would compete for the remainder of the season in non-Championship rounds, with no more than four cars entering each race.

A WSC car would score its first podium finish at Sebring with a second, and third place behind a Daytona winning GTS class Nissan 300ZX.

The car brand regularly achieving podium finishes every round after that, Oldsmobile, won the manufacturer's title over Ferrari by four points.

The Ferrari 333 SP and the R&S cars (Oldsmobile / Ford) were the dominant entries in the series from 1995 until the demise of IMSA at the end of 1998.

In 1996, Slater sold the organization to Roberto Muller (ex-CEO of Reebok) and Wall Street financier Andy Evans, who was also an IndyCar owner, and owner-driver of the Scandia WSC team.

Evans and VP of marketing Kurtis Eide were responsible for the name change to Professional Sports Car Racing.

Under tremendous pressure from team owners and management, Evans sold the series to PST Holdings, Inc., a group led by Raymond Smith, formerly the chief financial officer of Sports Car.

A breakaway series formed in 1998 involving the Sports Car Club of America, and was running under the name of the United States Road Racing Championship.

The series struggled early on, but after the introduction of the Daytona Prototype class, proved to be a popular competitor to the more international ALMS, attracting some pro drivers and teams, featuring large fields, and producing close competition.

[citation needed] Grand AM and ALMS merged in 2014 under IMSA sanction and France family ownership to create the WeatherTech SportsCar Championship.