Camel GT era The first champions were
Peter Gregg and
Hurley Haywood, in a Porsche 914-6 GTU. Common winners in these early years of IMSA were the
Porsche 911 Carrera RSR, and the
Chevrolet Corvette.
Camel became the title sponsor during the second season, with the series becoming known as the Camel GT Challenge Series. 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. Initially, all cars were identified with a category tag, stating which category they competed in, 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, as well as a Joe Camel decal. Starting fields of 30 or more competitors were not unusual during this era. One of the premiere race events was the Paul Revere 250, which started at midnight of the Fourth of July. The race was conducted entirely at night. In 1975 a new category, All American Grand Touring (AAGT), was introduced to counteract the Porsche dominance in GTO. 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. The car was not a success, however, and it became obsolete when the new GTP category was created. TU would be phased out in 1976, TO the following year. Turbochargers were not permitted until the middle of the 1977 season. They were allowed following protests by Porsche's motorsport department, after inspecting
Al Holbert's AAGT winning
Chevrolet Monza, which had won two titles. Prior to 1977, Porsche privateers struggled with obsolete 911 Carrera RSRs against the AAGT cars. Engine sizes were determined by IMSA officials, who had devised a set of rules to determine fair competition, using a displacement versus minimum weight formula. Turbochargers were taken into account as well as rotary power, fuel injection, and many other engine features. 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. The 935 became the most successful car in the series. The most successful driver of the 1970s was Peter Gregg, who won championships in 1971, 1973, 1974, 1975, 1978, and 1979. Twin turbos were outlawed at the end of the 1982 season after
John Paul Sr. and
John Paul Jr. dominated in a modified 935.
GT spaceframe era In 1984, all GT cars were required to display a large square decal to identify which category the car competed in. A GTU car, for instance, would have a black
U on white, and a GTO car, a white
O on black. All others had standard IMSA GT decals. One significant change to the rules during the 1980s was the 2.5 liter limit being increased to 3.0 liters, with the maximum 6.0 liter limit still in place.), the team faced the distinct possibility that they would be required to race a front-wheel-drive car, until they managed to persuade IMSA to change the rules, thereby permitting cars to race with something other than their original drivetrain, and therefore with a redesigned chassis. To AAR's delight, IMSA did change the rules, and the car was converted to rear wheel drive. One outstanding feature of the car was the
4T-GTE engine, from its
Safari Rally-winning,
Group B predecessor, producing around . thereby costing them both the manufacturer's and driver's titles,
Hans-Joachim Stuck driving. Another manufacturer to experience a run of wins was Mazda. After some success by the
Mazda RX-2 and
Mazda RX-3, the
Mazda RX-7 won its class in the IMSA
24 Hours of Daytona race an amazing ten years in a row, starting in 1982. It also won eight IMSA GTU championships in a row from 1980 through 1987. The car went on to win more IMSA races in its class than any other model of automobile, with its one hundredth victory on September 2, 1990.
GTP era GTP class car In 1981, purpose-built GTP cars (Grand Touring Prototypes) appeared in the championship, and were similar to the new FIA
Group C cars which would be introduced to the
World Endurance Championship from 1982. The main difference between the two categories was that the former had no emphasis on fuel consumption which was highlighted by
Derek Bell saying "Race fans do not come to races to watch an economy run." Camel Lights cars also used the same decal There were many other manufacturers in the GTP class, such as URD Rennsport, Spice,
Intrepid or Gebhardt, and in the early 1990s, Mazda.
Fall of GTP Following a successful heart surgery in 1987, Bishop began to rethink his priorities. He was approached by Mike Cone and Jeff Parker, owners of
Tampa Race Circuit. In January 1989, Bishop and France sold the series to Cone and Parker. The new owners relocated the IMSA headquarters from Connecticut to
Tampa Bay. Cone and Parker sold it to businessman Charles Slater. Both lost millions attempting to revive the sagging TV ratings. The GTP category was credited for many innovations in the U.S., including
antilock brakes,
traction control, and
active suspension. In 1995, in a bid to move closer to the European
BPR Global GT Series, the GT category would undergo another major reformatting. GTS became known as GTS-1, and GTU became known as GTS-2. In 1997, there was another category addition: GTS-2 became GTS-3. The new GTS-2 category was introduced to allow for the existing GT2 cars.
End of an era 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. Other owners included Dough Robinson and Tom Milner. In 2001
Don Panoz purchased PSCR to solidify the sanction for Panoz's
American Le Mans Series (ALMS) which had been sanctioned by PSCR since 1999. Panoz renamed the sanctioning organization IMSA, and it was the official sanctioning body of the American Le Mans Series, the Star Mazda series, and the
Panoz GT Pro series. The ALMS uses regulations based on those of the
24 Hours of Le Mans, but in 2005 the relationship between Panoz and the Le Mans organizers,
ACO, became problematic. 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. It was headed by a group of competitors that wanted to keep the rules within the United States. After failing by 1999, a new U.S.-based series was started with the full support of
NASCAR's
France family named the
Grand-Am Road Racing, operating the headlining
Rolex Sports Car Series. 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. Much like the split from 1996 to 2008 between
Champ Car and the
IRL, critics say this split was detrimental to the sport as a whole. Grand AM and ALMS merged in 2014 under IMSA sanction and France family ownership to create the
IMSA SportsCar Championship. The WeatherTech Championship is considered the official continuation. After the series' demise, a U.S.-based
historical racing organization, Historic Sportscar Racing, created a new series to put GTP and Group C cars that had been stored away back onto the track. The series was called HSR ThunderSport. Its creation sparked a similar revival series in Europe, as well as another series in the UK called Group C/GTP Racing. ==Champions==