IMSA GT classes are former classifications ofsports prototypes insports car racing competing in theIMSA GT Championship. The classes were used at different, overlapping times during the period from 1971 to 1998, over which the championship ran.
Grand Touring Over (GTO)[1] is the name of a former classification designated togrand touring cars competing in the IMSA GT Championship, and later byGrand-Am in theRolex Sports Car Series. IMSA used the class between 1971 and 1991,[2] and Grand-Am used the class for a single season in 2000. The class had its origins in the original "TO" class used by the SCCA in theTrans-Am series, and was also similarly modeled to theFIA'sGroup 4 andGroup 5 racing classes, but eventually evolved over time into its own category.[3] The class specified anengine displacement of more than 2.5 L (150 cu in), with engine design and number of cylinders being unrestricted.Turbocharging andsupercharging was allowed on engines up to a size of 6.0 L (370 cu in). Engines over 6.0 L (370 cu in) were required to benaturally aspirated. The original class became known asGrand Touring Supreme (GTS) in 1992.[4]
| Brand | Chassis | Image | Debut |
|---|---|---|---|
| Alfa Romeo | Montreal | 1974 | |
| AMC | AMX | 1980 | |
| Gremlin | 1975 | ||
| Javelin | 1974 | ||
| Hornet | 1971 | ||
| Spirit | 1984 | ||
| Spirit AMX | 1981 | ||
| Avanti II | 1983 | ||
| Audi | 90 Quattro |  | 1989 |
| BMW | 2002 TI | 1973 | |
| 3.0 CSL | 1974 | ||
| 3.5 CSL | 1977 | ||
| 320i | 1977 | ||
| M1 | 1981 | ||
| Buick | Skyhawk | 1984 | |
| Skylark | 1980 | ||
| Somerset | 1987 | ||
| Chevrolet | Corvette | 1971 | |
| Corvette C2 Sting Ray | 1980 | ||
| Corvette C3 | 1980 | ||
| Corvette C4 | 1988 | ||
| Corvette ZR-1 | 1991 | ||
| Monza | 1977 | ||
| Nova | 1980 | ||
| Datsun | 240Z | 1980 | |
| 280ZX | 1980 | ||
| 280ZX Turbo | 1981 | ||
| De Tomaso | Pantera | 1976 | |
| Ferrari | 365 GT4 BB | 1975 | |
| 512 | 1985 | ||
| 512 BB | 1985 | ||
| Ford | Maverick | 1983 | |
| Mustang Cobra |  | 1983 | |
| Jaguar | XK-E | 1974 | |
| Mazda | RX-7 | 1981 | |
| Mercury | Capri | 1982 | |
| Cougar XR-7 | 1989 | ||
| Merkur | XR4Ti |  | 1988 |
| Nissan | 300ZX Turbo | 1989 | |
| Oldsmobile | Calais | 1986 | |
| Starfire | 1982 | ||
| Toronado |  | 1986 | |
| Plymouth | Volaré | 1981 | |
| Pontiac | Astre | 1977 | |
| Firebird | 1980 | ||
| Firebird Trans Am | 1980 | ||
| Porsche | 911 |  | 1973 |
| 924 Carrera GTR | 1981 | ||
| 928 | 1984 | ||
| 934 | 1980 | ||
| 944 Turbo | 1987 | ||
| Shelby | Mustang | 1971 | |
| Toyota | Celica | .jpg) | 1983 |
| Celica Turbo | 1986 | ||
| Celica Turbo ST165 | 1988 | ||
| Triumph | TR8 | 1980 | |
Grand Touring Under (GTU) was a classification originally used in the IMSA GT Championship,[5] and later byGrand-Am in theRolex Sports Car Series.[6] IMSA used the class between 1971 and 1994, and Grand-Am used the class for a single season in 2000.[7] The original class rules specified anengine displacement of under 2.5 L (150 cu in),natural aspiration, and was the secondary class below the top tier class,GTO. The class later became known asGTS-2 in 1995, thenGTS-3 between 1996 and 1997, and eventually evolved into theGT3 class for 1998.[8][9]
All American Grand Touring (AAGT)[10] was maintained by IMSA between 1975 and 1989.[11] These cars were All-American,V8-powered, used a maximum of 5 forward gears, and used asteeltube frame (similar to the type used in theSCCATrans-Am Series), and were designed to compete against heavyweight European manufacturers and machinery of the time, such asPorsche andBMW, who were dominating the series at the time.[5][6][12]
Ford:
American Challenge, also known as theAll American Challenge, and formally known as theKelly American Challenge, was a category and set of regulations for the IMSA GT Championship between 1977 and 1989. Similar to theAAGT class, these cars were All-American, use a maximum of 5 forward gears, and use asteeltube frame (similar to the type used inSCCATrans-Am Series cars).[13][14]
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Grand Touring Experimental (GTX)[15] is a former classification maintained by IMSA between 1977 and 1982. Some cars were based onFIAGroup 5 rules; such as thePorsche 935, and some cars were based onFIAGroup 6 regulations, such as theLola T600. Like the originalGTO class, the class rules specifiedturbocharging andsupercharging was allowed on engines up to a size of 6.0 L (370 cu in); with engine design and number of cylinders being free and unrestricted. Engines over 6.0 L (370 cu in) were required to benaturally-aspirated.[5][6][16][17]
Grand Touring Prototype (GTP) was maintained byIMSA between 1981 and 1993.[5][6] The early cars were based on the almost same identical ruleset as theFIA'sGroup C category, but eventually evolved into a separate category. It was the successor to theGrand Touring Experimental (GTX) class, which were based onFIAGroup 5 andGroup 6 cars.[17][19][9]
The IMSA GTP moniker was revived in 2023 to replace DPi as the top class of theIMSA SportsCar Championship for the merger of DPi and theWorld Endurance Championship Hypercar class.
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In 1981, purpose-built GTP cars (Grand Touring Prototypes) appeared in the championship, and were similar to the new FIAGroup C cars which would be introduced to theWorld Endurance Championship from 1982. The main difference between the two categories was that the former had no emphasis on fuel consumption which was highlighted byDerek Bell saying "Race fans do not come to races to watch an economy run."[20]Brian Redman was the first GTP champion, driving aLola T600 with a Chevrolet engine.March also fielded prototypes, withAl Holbert winning the 1983 championship with a Chevrolet powered car, changing to Porsche power later in the season; andRandy Lanier a year later with Chevrolet power. 1984 also saw the introduction of thePorsche 962, which dominated the series from '85 to '87.Nissan then took control of the series in 1988, but faced challenges fromJaguar,Porsche, andToyota throughout the next three years. Toyota was quickest in 1992 and 1993, at the end of the GTP era, asDan Gurney'sAll American Racers team campaigned theEagle 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 bySpice Engineering. Other well known participants were theTiga,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 aP being added to denote their category.[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 orGebhardt, and in the early 1990s, Mazda.
Following a successful heart surgery in 1987, Bishop began to rethink his priorities. He was approached by Mike Cone and Jeff Parker, owners ofTampa Race Circuit. In January 1989, Bishop and France sold the series to Cone and Parker. The new owners relocated the IMSA headquarters fromConnecticut toTampa Bay.[20] Bishop would stand down as president in favor of Mark Raffauf, who was his deputy, and its representative on the ACCUS board.[23] Cone and Parker sold it to businessman Charles Slater. Both lost millions attempting to revive the sagging TV ratings.[20]
By 1992, there were a number of factors that led to the decline of the GTP category. Porsche concentrated on itsIndyCar (Porsche 2708) program when critics stated that theZuffenhausen marque should have built a followup to its962.[20] 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 due to Holbert's death in an aircraft accident later in the year.[20] For some, much of the blame was on the organization for allowing the Japanese "works" teams to dominate the series. Under Bishop's original vision, privateers and "works teams" were able to race equally. Privateer teams walked away, while the Japanese economy started to go downhill. These factors led Nissan and Mazda to leave the series. Critics predicted that the decreased variety of cars would disappoint race fans, and in fact, it did finally kill the series in 1993.[20] GTP cars ran their last race on October 2, 1993, atPhoenix International Raceway.[24]
The GTP category was credited for many innovations in the U.S., includingantilock brakes,traction control, andactive suspension.[20] Dave Cowart and Kemper Miller'sRed Lobster sponsored team of the early 1980s would innovate race team hospitality, practices which were subsequently adopted by virtually every other team.[20] For those that competed, GTP was recognized for itscamaraderie among drivers, especially rivals. ButHans Stuck, commenting in theforeword of the book"Prototypes: The History of the IMSA GTP Series", sarcastically compared the series' camaraderie to Formula One's lack of such.[20]
| Brand | Chassis | Image | Debut | Applications | Notes |
|---|---|---|---|---|---|
| Alba | AR3 |  | 1984 | GTP Lights | |
| AR4 | 1985 | GTP Lights | |||
| AR8 | 1986 | GTP | |||
| All American Racers | Eagle HF89 |  | 1989 | GTP | |
| Eagle HF90 |  | 1990 | GTP | ||
| Eagle MkIII |  | GTP | |||
| Argo | JM16 | 1984 | GTP Lights | ||
| JM19 | .jpg) | 1985 | GTP Lights | ||
| BMW | GTP |  | 1986 | GTP | Built off aMarch 86G. |
| Chevrolet | Corvette GTP |  | 1984 | GTP | |
| Ferrari | 512 BB | 1982 | |||
| Ford | Mustang GTP | 1983 | GTP | ||
| Mustang Maxum GTP | .JPG) | 1987 | GTP | ||
| Probe GTP | 1985 | GTP | |||
| Jaguar | XJR-5 |  | 1982 | GTP | |
| XJR-7 |  | 1985 | GTP | ||
| XJR-9 |  | 1988 | GTP | ||
| XJR-10 | .jpg) | 1989 | GTP | ||
| XJR-12 |  | 1990 | GTP | ||
| XJR-16 |  | 1991 | GTP | ||
| Kudzu | DG-1 | 1989 | GTP Lights | ||
| DG-2 | 1992 | GTP Lights | |||
| DG-3 | .jpg) | 1993 | GTP Lights | ||
| Lola | T600 |  | 1981 | GTP | |
| T610 | 1982 | GTP | |||
| T616 | 1984 | GTP | |||
| March | 82G | 1984 | GTP | ||
| 83G | .jpg) | 1982 | GTP | ||
| 84G |  | 1983 | GTP | ||
| 85G |  | 1984 | GTP | ||
| 86G |  | 1986 | GTP | Used as a base for theBMW GTP,Nissan R86V, andNissan R88C. | |
| Mazda | 757 |  | 1986 | GTP | |
| 767 | 1988 | GTP | |||
| 767B |  | 1989 | GTP | ||
| GTP | 1983 | GTP | |||
| RX-792P | .jpg) | 1992 | GTP | ||
| Nimrod | NRA/C2 |  | 1983 | GTP | |
| Nissan | GTP ZX-Turbo |  | 1985 | GTP | |
| NPT-90 |  | 1990 | GTP | ||
| Porsche | 962 |  | 1984 | GTP | |
| Pratt & Miller | Intrepid RM-1 | .jpg) | 1991 | GTP | |
| Spice | SE86C |  | 1986 | GTP Lights | |
| SE88P | 1988 | GTP, GTP Lights | |||
| SE89P | .jpg) | 1989 | GTP | ||
| SE90P |  | 1990 | GTP | ||
| SE91P |  | 1991 | GTP Lights | ||
| SE92P | .jpg) | 1992 | GTP | ||
| Tiga | GT286 | 1986 | GTP Lights | ||
| Toyota | 88C |  | 1989 | GTP |
Grand Touring Supreme (GTS) is a former classification originally by IMSA and later byGrand-Am in theRolex Sports Car Series. IMSA used the class between 1992 and 1997, and Grand-Am used the class between 2001 and 2003. It was an evolution and re-branding of the formerGrand Touring Over (GTO) class. Like the original GTO class, the class rules specified anengine displacement of more than 2.5 L (150 cu in), with engine design and number of cylinders being free and unrestricted.turbocharging andsupercharging was allowed on engines up to a size of 6.0 L (370 cu in). Engines over 6.0 L (370 cu in) were required to benaturally-aspirated. Between 1995 and 1996 in the IMSA GT Championship, the top GTS class became known asGTS-1, while the formerGrand Touring Under (GTU) class became known asGTS-2. This changed again in 1997, when the GTS-2 (former GTU) class became known asGT3, due to the addition of a new GTS-2 category, which allowed for existing internationalGT2 cars, like those used in theFIA GT Championship.[7] IMSA also used theGTS designation for the formerGT2 class cars of cars (later known as GT1) in theAmerican Le Mans Series, between 1999 and 2004.
