IMSA GT Championship


IMSA GT was a sports car racing series organized by International Motor Sports Association. Races took place primarily in the United States and occasionally in Canada.

History

The series was founded in 1969 by John and Peggy Bishop, and Bill France, Sr. Racing began in 1971, and was originally aimed at two of FIA's stock car categories, running two classes each; the GT and touring classes. 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.
For the following year, John Bishop brought in sponsor R. J. Reynolds, and in 1975 introduced a new category: All American Grand Touring. In 1977, the series went through a series of major changes. IMSA permitted turbocharged cars to compete for the first time, as well as introducing a new category: GTX, based on Group 5 rules. In 1981, after Bishop decided to not follow FIA's newly introduced Group C rules, he introduced the GTP class for sports prototypes. In 1989, Bishop sold off his organization. After a period of decline in the early 1990s, the Sports Racer Prototype category was introduced in 1993 to replace the top IMSA GTP category in 1994. In deference to the series deviating from the FIA's naming of the class to Sports Racers and Le Mans Prototypes by the French Automobile Club de l'Ouest in Europe for their then separate series, the new class was designated IMSA World Sports Car.
After a period of multiple ownerships, the organization, by then owned by Don Panoz, was eventually renamed Professional Sports Car Racing. In 1999, PSCR decided to affiliate with the Automobile Club de l'Ouest and adopt the sanctioning body's rule book, renaming the series the American Le Mans Series. Despite having various official names, the GT series was known commonly as the "IMSA series", as it was the sanctioning body. For legal reasons, both the 1999-2013 ALMS and the current WeatherTech SportsCar Championship are regarded as a continuation of the original IMSA GT Championship.

Initial divisions

The 1971 season was the first racing season, and lasted six races. The early years of the series featured GT cars, similar to the European Group 2 and Group 4 classes, divided into four groups:
  • GTO - Grand touring-type cars with engines of 2.5L displacement or more, the letter O meaning "over 2.5L". The GTO class was dominated by Corvettes, then by Shelby Mustangs, and then various factory teams consisting of Cougars, 280zxs, Celicas and finally, 300ZXs.
  • GTU - Grand touring-type cars with engines of 2.5L displacement or less, the letter U meaning "under 2.5L". The GTU group was dominated by Porsche 914-6 GTs, and SA22 Mazda RX-7s through the end of the 1980s.
  • TO - Touring-type cars, such as the Chevrolet Camaro with engines of 2.5L or more displacement
  • TU - Touring-type cars with engines of 2.5L or less displacement
In essence, these groups had been absorbed from the Trans Am Series. Trans Am would quickly become a support series for IMSA GT.

History of the top series in the GT Championship

Camel GT era

The first champions were Peter H. 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, 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, 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. 3.0L cars were required to weigh, whereas 6.0L cars had to weigh no less than. In an effort to equalize the competition, two-valve turbocharged cars were required to weigh 15% more, and four-valve turbocharged cars 20% more. Electronic fuel injection became common, while ground effects were still prohibited.
Steering, braking, transmission, and suspension were left up to the constructor. Bigger, more powerful engines were permitted under homologation rules. The number of valves, ports, and spark plugs were not allowed to be modified from the original configuration.
The AAR Toyota team suddenly encountered a daunting problem with the rules when, with Toyota's introduction of the new, fourth generation, Celica for the US market, and the team's first entry into the top-flight GTO category, 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. 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. Utilizing the same engine, it became dominant once again. Other teams would follow this example, with notable cars such as the Chevrolet Beretta and the Mazda MX-6.
The Celica was one of just a few cars that had broken away from its production GT derivatives of the earlier years. With a full spaceframe chassis, they became serious race cars. By 1987, the category became dominated by factory teams, with testing sessions becoming common, and rules tailored to welcome them in rather than turn them away. Otherwise, the cars were required to closely resemble their showroom counterparts, though fenders could be widened, increasing the track up to.
There were no restrictions on body materials, as most teams favored removable, easy to repair fiberglass.
Another car that exploited the rules was the Audi 90. With its advanced Quattro four-wheel-drive system, the car had the potential to dominate during the 1989 season. The car performed well, but faced heavy competitions from two factory teams; the Roush Racing Mercury Cougar XR7, and Clayton Cunningham Racing's Nissan 300ZX, which took seven wins out of fifteen. Audi stayed away from the early season endurance classics, and had two cars drop out of the race in two different rounds, 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

In 1981, purpose-built GTP cars 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." Brian Redman was the first GTP champion, driving a Lola T600 with a Chevrolet engine. March also fielded prototypes, with Al Holbert winning the 1983 championship with a Chevrolet powered car, changing to Porsche power later in the season; and Randy Lanier a year later with Chevrolet power. 1984 also saw the introduction of the Porsche 962, which dominated the series from '85 to '87. Nissan then took control of the series in 1988, but faced challenges from Jaguar, Porsche, and Toyota throughout the next three years. 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. Along with the GTP cars, the Camel Lights cars, a smaller capacity, non-turbocharged, lower powered prototype category was introduced in 1985. Argo Racing Cars was the first 'Lights' Champions, followed by Spice Engineering. Other well known participants were the Tiga, Royale, Alba, Fabcar, and Kudzu.
Starting with the 1986 season, the GTP category had their own decal, which was similar to the IMSA GT side decal, with a P being added to denote their category. 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.