IMSA GT Championship

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IMSA GT Championship
File:The logo of the International Motor Sports Association Grand Touring Championship.jpg
Category Sportscar racing
Country North America
Inaugural season 1971
Folded 1998
(front to rear) Tommy Kendall and Wayne Taylor (both driving an Intrepid RM-1) leads eventual winner Davy Jones (Jaguar XJR-16) and Chip Robinson, followed by Geoff Brabham (both in Nissan NPT-91), Raul Boesel (XJR-16) and James Weaver (Porsche 962) in the Nissan Grand Prix of Ohio, at Mid-Ohio Sports Car Course, 1991[1][2]

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.


The series was founded in 1969 by John and Peggy Bishop[3] and Bill France, Sr.,[4] and racing debuted in 1971. It was originally aimed at two of FIA's stock car categories running at two different classes, the GT (Group 3 and 4) and Touring (Group 1 and 2) cars. The first race was held at Virginia International Raceway; it was an unexpected hit with both the drivers and a handful of spectators who attended.[5]

For the following year, IMSA founder John Bishop brought in sponsor R. J. Reynolds and in 1975, introduced a new category called All American Grand Touring (AAGT). In 1977, the series would go through a series of major changes. IMSA permitted turbocharged cars for the first time as well as introducing a new category called GTX for cars based on the Group 5 rules. In 1981, after Bishop decided to not follow FIA's newly introduced Group C rules, so 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 Worlds Sports car category was introduced in 1993 to replace the GTP category in 1994.

After a period of multiple ownerships, the organization was eventually renamed Professional Sports Car Racing (PSCR). In 1999, PSCR decided to drop their own championship in order to sanction a new American Le Mans Series. Despite various names, the GT series was known commonly as the IMSA series as it had been the organization's dominant series.

Initial divisions

Robin McCall in the Hoerr Racing GTO Oldsmobile (1987).

The 1971 season was the first racing season, and featured 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 cars were Grand Touring type cars with an engine of 2.5 L displacement or more,[5] the letter "O" colloquially meaning "Over 2.5L". The GTO group was dominated by Corvettes, then by Shelby Mustangs and then various factory teams consisting of Cougars, 280zx, Celicas and finally, the 300ZX.
  • GTU cars were Grand Touring type cars with engines of 2.5 L displacement or less, the letter "U" colloquially meaning "Under 2.5L". The GTU group was dominated by Porsche 914-6 GTs and SA22 Mazda RX-7s (1978–1985) through the end of the 1980s.
  • TO were touring-type cars such as the Camaro with an engine of 2.5 L or more displacement.
  • TU were touring-type cars with an engine of 2.5 L 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

The 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 Chevrolet Corvette. Camel became the title sponsor during the second season, and the series became known as "Camel GT Challenge Series". The sponsor's corporate decal had to be displayed in a visible manner on the left and right side of the car, and its patch on the Nomex driver's uniform's breast area, featuring Joe Camel smiling and smoking a cigarette while driving a race car.[6]

Initially, cars were marked visibly with its category tag, stating which category they belong,[7] but onward from the middle of the 1975 season, all cars within the series had to bear a rectangular IMSA GT decal, which incorporated its logo on the left followed by a large GT tag.[8] as well as 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 the stroke of midnight of the 4th of July. The race was conducted entirely during the night from start to finish.[citation needed]

In 1974 a new category called All American Grand Touring (AAGT) was introduced to counteract the Porsche dominance in GTO.[9]

This category did not run without controversy. In 1981, 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. This car was not a success and became obsolete when the new GTP category was created.[10] The TU would be phased out in 1976 along with the TO for the following year.

Turbochargers were not permitted until the mid-1977 season. They became permitted after 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.[11]

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.[12]

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.[citation needed] The most successful driver of the seventies was Peter Gregg, who won championships in 1971, 1973, 1974, 1975, 1978, and 1979. Twin turbos were eliminated at the end of the 1982 season after John Paul, Sr. and John Paul, Jr. dominated in a modified 935.

The GT spaceframe era

In 1984, GT cars were required to bear a large square decal to determine which category each cars are represented in, GTU would therefore bear a black U on white[13] and white O on black to represent GTO.[14] All others only bore their standard IMSA GT decals.[15]

One significant change to the rules during the 1980s was the 2.5 liter ceiling having been changed to 3.0 liters, with the maximum of 6.0 liter ceiling still in place.[12] 3.0L cars were required to weigh 1,900 lb (860 kg), whereas 6.0L weighed no less than 2,700 lb (1,200 kg). 2-valve turbocharged cars were given an extra 15% weight and 4-valve turbocharged cars 20% extra. Electrical fuel injection was to become common and ground effects were prohibited.[12]

Steering, braking, transmission and suspension were left up to the constructor. Bigger and more powerful engines were permitted under homologation rules.[12] The number of valves, ports and spark plugs were not allowed to be changed from the original configuration.

The AAR Toyota team made use of a loophole in the rules when, with its introduction of the new fourth generation Celica for the US market and the team's first entry into the top flight GTO category (despite not having to win one single GTU title[16]), the team faced the possibility that they would be required to race a front wheel drive car until they managed to persuade IMSA to rework the rules, determining that a car does not have to race in its original drivetrain, and therefore with a redesigned chassis, the car was converted to rear wheel drive.[17] Another advanced features is the 4T-GT engine, from its Safari Rally winning Group B predecessor producing of around 475 hp (354 kW).[12] and its features mentioned above. Piloted by the likes of Chris Cord, Willy T. Ribbs and Dennis Aase, the car was proven to be dominant within its class until the teams defection to GTP, utilizing the same engine, becoming dominant once again. Other teams would follow this example, notably Chevrolet Beretta (in the Trans-Am series) and Mazda MX-6 (in IMSA GTU).[17]

The Celica was one of the few examples of cars that had broken away from their production GT derivatives of the earlier years as with 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, cars were required to resemble their showroom counterpart, though fenders could be widened up to 79 inches (2,000 mm).[12]

There were no restrictions to body materials as most teams favored removable fiberglass, meaning one of the only remaining panels from a car's production counterpart was the sheet steel roof.

Another car that exploited the rule system was Audi's 90. With its advanced four wheel drive system, the car had a potential to become a dominant car during the 1989 season. The car performed well, but faced heavy competitions from two factory teams, Roush Racing Mercury Cougar XR7 and Clayton Cunningham Racing Nissan 300ZX, which took seven wins out of fifteen, as Audi stayed away from the early season endurance classics (Daytona and Sebring) as well as having two cars out of the race in two different rounds,[18] thereby costing them the title for both make and driver Hans-Joachim Stuck.

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 ten years in a row, starting in 1982, and won the IMSA GTU championship each year 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.[19]

The GTP Era

Toyota Eagle Mk.III GTP class car

In 1981, purpose-built GTP cars (Grand Touring Prototypes) appeared in the championship, these being 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 the former had no emphasis on fuel consumption which was highlighted by Derek Bell quoting "race fans do not come to races to watch an economy run!".[9] Brian Redman was the first champion of the GTPs, driving a Lola T600 with a Chevrolet engine. March also fielded prototypes, in which Al Holbert won 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 1985 to 1987. Nissan then took control of the series in 1988, but faced challenges from Jaguar, Porsche, and Toyota throughout the proceeding three years. Toyota was quickest in 1992 and 1993 at the end of 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 were the first Lights champions, followed by Spice. Other well known participants were the Tiga, Royale, Alba, Fabcar, and Kudzu.

Starting from the 1986 season, the GTP category had their own decal, which similar to the IMSA GT side decal, an extra P was added to denote their category,[20] Camel Lights cars also bore the same decal[21]

There were many other manufacturers in the GTP class, such as URD, 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, owner 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.[9] Bishop would stand down as president in favor of Mark Raffauf, who was his deputy and its representative on the ACCUS board.[22] Cone and Parker sold it to businessman Charles Slater. Both lost millions attempting to revive the sagging TV ratings.[9]

By 1992, there were a number of factors that led to the decline of the GTP category. Porsche concentrated on its IndyCar program when critics stated that the Zuffenhausen marque should have built a followup of its 962.[9] Back in 1988, Al Holbert realized that the 962 was beginning to feel dated. He proposed a follow up open top Porsche powered racer which would also be sold to customer teams. That project never got off the ground after Holbert's death in an aircraft accident later in the year.[9] For some, much of the blame was on organization to allow the Japanese works teams to dominate the series. Under Bishop's original vision, privateers and works were able to race equally. Privateer teams walked away, and the Japanese economy started to go downhill. These factors led Nissan and Mazda to walk away from the series. Critics say that the diminished variety of cars that would disappoint race fans which would finally kill the series in 1993.[9] GTP cars ran their last race on October 2, 1993 at Phoenix International Raceway.[23]

The GTP category was credited for many innovations in the U.S. including antilock brakes, traction control, and active suspension.[9] Dave Cowart and Kemper Miller's Red Lobster sponsored team of the early 1980s would innovate racing team hospitalities which became adopted by virtually every other teams in the future.[9] But for those who competed, it was credited for its camaraderie within drivers, especially rivals. Hans Stuck, commenting in the foreword of the book Prototypes: The History of the IMSA GTP Series, sarcastically compared the series' camaraderie to Formula One's lack of such.[9]

World Sports Cars

With rising costs and factory teams walking away from the series which meant diminishing entries, IMSA introduced a new prototype category for in 1993 called World Sport Car (WSC). The WSC replaced the GTP and Lights closed-top cars for the following year. The WSC cars were open-top, flat-bottomed sports-prototypes with production engine as opposed to racing versions of production engines from GTP cars.

The WSC cars made their debut at the Miami Grand Prix with a sole entry of Brent O'Neill. The car finished last among the cars that were still running. After skipping the 12 Hours of Sebring, the category would compete for the remainder of the season as non-championship rounds, with no more than four cars entering. In 1994 Camel would be replaced by Exxon as the title sponsor. However, as the WSC cars took over as the leading category, their reliability would be tested at the opening round at the 24 Hours of Daytona. Two cars started on the front row, with eight WSC cars competing. Two cars finished the race, with the leading WSC car finishing ninth behind GT cars. The WSC cars would score its first podium finish at Sebring with a second and third place behind a Daytona winning GTS category Nissan 300ZX. That led to a rule change for the latter category as they would be barred from using engines that were originally for GTP cars. At the inaugural round for WSC cars at Road Atlanta, the new Ferrari 333 SP would make its debut in a mass media fanfare and win its debut race. The car regularly appearing on the podium on every round after that. Oldsmobile won the manufacturer's title over Ferrari by four points.

In 1995, a new rival for Ferrari appeared in the Riley & Scott Mk III. The car would make its debut at Daytona, but would retire after the eleventh lap after an engine failure. Ferrari would help the category to score an overall win at the 12 Hours of Sebring, and would take the title for both makes and driver. The Ferrari and the R&S cars were the dominant racers of the series from 1995 to 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 also was 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 (PSCR).

In 1992, the long running category American Challenge would step into the GT series. It became known as the GTO category when the former GTO category was renamed to GTS (Grand Touring Supreme). The move was prompted by sponsor Exxon, who wanted the series named after its subbrand of fuel.[24] In 1995, in a bid to move close to the European BPR Global GT Series, the GT category would undergo another major reformat. 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, new GTS-2 category was announced 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 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. Don Panoz renamed the sanctioning organization as IMSA and it is now 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, has become problematic.

A breakaway series formed in 1998 involving the Sports Car Club of America and running under the name of the United States Road Racing Championship. It was headed by a group of competitors wanting to keep rules within the United States. After failing by 1999 a new US based series was started with the full support of NASCAR's France family named the Grand American Road Racing Association, operating the headlining Rolex Sports Car Series. The series struggled early on, but after the introduction of the Daytona Prototype class, has proven to be a popular competitor to the more international ALMS, attracting some pro drivers and teams, large fields, and 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.[citation needed] Grand AM and ALMS merged in 2014 under IMSA sanction to create the United SportsCar Championship.

After the series demise, a US-based historical racing organization, Historic Sportscar Racing (HSR) created a new series to put GTP and Group C cars that had been stored away to be put back onto the track, the series was called HSR ThunderSport, this would spark another similar revival series in Europe which then another UK based series would be formed called Group C/GTP Racing.


1971 United States Dave Heinz United States Peter Gregg
United States Hurley Haywood
1972 United States Phil Currin United States Hurley Haywood
1973 United States Peter Gregg United States Bob Bergstrom
1974 United States Peter Gregg United States Walt Maas
1975 United States Peter Gregg United States Bob Sharp
1976 United States Al Holbert United States Brad Frisselle
1977 United States Al Holbert United States Walt Maas
United States Peter Gregg United States Dave Cowart United States Dave White
1979 United States Peter Gregg United States Howard Meister United States Don Devendorf
1980 United Kingdom John Fitzpatrick Dominican Republic Luis Mendez United States Walt Bohren
1981 United Kingdom Brian Redman United States Dave Cowart United States Len Mueller
1982 GTP IMSA Lights GTO GTU
United States John Paul Jr. Porsche 935 - United States Don Devendorf United States Jim Downing
1983 United States Al Holbert March 83G - United States Wayne Baker United States Roger Mandeville
1984 United States Randy Lanier March 83G - United States Roger Mandeville United States Jack Baldwin
1985 United States Al Holbert Porsche 962 United States Jim Downing Canada John Jones United States Jack Baldwin
1986 United States Al Holbert Porsche 962 United States Jim Downing United States Scott Pruett United States Tommy Kendall
1987 United States Chip Robinson Porsche 962 United States Jim Downing United States Chris Cord United States Tommy Kendall
1988 Australia Geoff Brabham Nissan GTP ZX-Turbo United States Tom Hessert United States Scott Pruett United States Tommy Kendall
1989 Australia Geoff Brabham Nissan GTP ZX-Turbo United States Scott Schubot United States Peter Halsmer United States Bob Leitzinger
1990 Australia Geoff Brabham Nissan GTP ZX-Turbo Mexico Tomas Lopez United States Dorsey Schroeder United States Lance Stewart
1991 Australia Geoff Brabham Nissan NPT-91 United States Parker Johnstone United States Peter Halsmer United States John Fergus
1992 Argentina Juan Manuel Fangio II Toyota Eagle MKII United States Parker Johnstone United States Irv Hoerr United States David Loring
1993 Argentina Juan Manuel Fangio II Toyota Eagle MKII United States Parker Johnstone United States Charles Morgan United States Butch Leitzinger
South Africa Wayne Taylor Kudzu-Mazda United States Joe Pezza United States Jim Pace
1995 WSC GTS-1 GTS-2
Spain Fermín Vélez Ferrari 333 SP United States Irv Hoerr Costa Rica Jorge Trejos
1996 South Africa Wayne Taylor Riley & Scott-Oldsmobile United States Irv Hoerr United States Larry Schumacher
1997 United States Butch Leitzinger Riley & Scott-Ford United States Andy Pilgrim United States Larry Schumacher
1998 United States Butch Leitzinger Riley & Scott-Ford United Kingdom Andy Wallace United States Larry Schumacher

See also


  1. "IMSA GT 1991 season". WSRP. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  2. "Racing Sports Cars". Racing Sports Cars. 1991-02-06. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  3. "Peggy Bishop, wife of IMSA founder, dies - Autoweek Racing Grand-Am news". Autoweek. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  4. "Grand-Am, American Le Mans to merge series". Retrieved 5 September 2012.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  5. 5.0 5.1 "IMSA blog: Do you want to know about GT racing in the 70s". 2006-01-06. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  6. Photo by courtesy of: Mark Windecker. "Mid-Ohio 6 Hours 1973". Racing Sports Cars. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  7. Photo by courtesy of: Mark Windecker. "Mid-Ohio 6 Hours 1973". Racing Sports Cars. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  8. Photo by courtesy of: Gene Felton Restorations. "Laguna Seca 100 Miles I 1975". Racing Sports Cars. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  9. 9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 Prototypes: The History of the IMSA GTP Series, J. A. Martin & Ken Wells, David Bull Publishing, ISBN 1-893618-01-3
  10. Essential Datsun Z 240Z to 280Zx: The Cars and Their Story 1969-83, Colin Shipway, Motorbooks International, ISBN 1-870979-51-6
  11. 930 to 935: The Turbo Porsches, John Starkey, Renwick & Starkey Ltd. ISBN 0-9665094-1-2
  12. 12.0 12.1 12.2 12.3 12.4 12.5 "IMSA blog: GTO : the big step ahead". 2007-02-06. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  13. Photo by courtesy of: Mark Windecker. "Daytona 24 Hours 1984". Racing Sports Cars. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  14. Photo by courtesy of: Mark Windecker. "Daytona 24 Hours 1984". Racing Sports Cars. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  15. Photo by courtesy of: Fred Lewis Photos. "Daytona 24 Hours 1984". Racing Sports Cars. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  16. "IMSA blog: All American Racers : part 1, the GT cars". 2006-07-27. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  17. 17.0 17.1 "The Angriest Celicas by Matthew Hayashibara, Sports Compact Car, September 1999". Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  18. "1989 IMSA GTO makes". WSPR Racing. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  19. "IMSAblog: Mazda RX7 : winningest car ever". 2006-02-14. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  20. Photo by courtesy of: Fred Lewis Photos. "Daytona 24 Hours 1986". Racing Sports Cars. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  21. Photo by courtesy of: Michael O. Crews. "Daytona 24 Hours 1986". Racing Sports Cars. Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  22. Endurance Racing 1982-1991, Ian Briggs, Osprey Automotice, ISBN 1-85532-228-5
  23. Michael Strahan (December 1993). "The Last Race". Car Magazine. Retrieved 2007-05-15.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  24. "". Retrieved 2014-06-23.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>

External links