IMSA GT Championship

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

• GTO - Grand touring-type cars with engines of 2.5L displacement or more,
  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 (1978–1985) 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

History of the top series in the GT Championship

Camel GT era

The first champions were

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.

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. ^{[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. The car was not a success, however, and it became obsolete when the new GTP category was created.^[11] 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.^[12]

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.^[13]

As a result, the new premier class known as GTX (Grand Touring Experimental, which was based on

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,[14] and a GTO car, a white O on black.^[15] All others had standard IMSA GT decals.^[16]

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.^[13] 3.0L cars were required to weigh 1,900 lb (860 kg), whereas 6.0L cars had to weigh no less than 2,700 lb (1,200 kg). 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.^[13]

Steering, braking, transmission, and suspension were left up to the constructor. Bigger, more powerful engines were permitted under homologation rules.^[13] 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 (despite not having won a single GTU title^[17]), 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.^[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. Utilizing the same engine, it became dominant once again. 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).^[18]

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

In 1981, purpose-built GTP cars (Grand Touring Prototypes) appeared in the championship, and were similar to the new FIA

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.^[21] Camel Lights cars also used the same decal^[22]

There were many other manufacturers in the GTP class, such as URD Rennsport, Spice,

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 due to engine failure. Ferrari would help the category score an overall win at the 12 Hours of Sebring, and would take the manufacturer's title. 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

In 1992, the long running category American Challenge stepped into the GT series. It became known as the GTO category when the former GTO category was renamed GTS (Grand Touring Supreme). The move was prompted by sponsor Exxon, who wanted the series named after its sub-brand of fuel.[25] 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

After the series' demise, a U.S.-based

]

Champions

Year	GTO			GTU
1971	Dave Heinz			Peter Gregg Hurley Haywood
1972	Phil Currin			Hurley Haywood
1973	Peter Gregg			Bob Bergstrom
1974	Peter Gregg			Walt Maas
1975	Peter Gregg			Bob Sharp
1976	Al Holbert			Brad Frisselle
1977	Al Holbert			Walt Maas
1978	GTX			GTO		GTU
	Peter Gregg			Dave Cowart		Dave White
1979	Peter Gregg			Howard Meister		Don Devendorf
1980	John Fitzpatrick			Luis Mendez		Walt Bohren
1981	Brian Redman			Dave Cowart		Len Mueller
1982	GTP			GTO		GTU
	John Paul Jr.	Porsche 935		Don Devendorf		Jim Downing
1983	Al Holbert	March 83G		Wayne Baker		Roger Mandeville
1984	Randy Lanier	March 83G		Roger Mandeville		Jack Baldwin
1985	GTP		Lights	GTO		GTU
	Al Holbert	Porsche 962	Jim Downing	John Jones		Jack Baldwin
1986	Al Holbert	Porsche 962	Jim Downing	Scott Pruett		Tommy Kendall
1987	Chip Robinson	Porsche 962	Jim Downing	Chris Cord		Tommy Kendall
1988	Geoff Brabham	Nissan GTP ZX-Turbo	Tom Hessert	Scott Pruett		Tommy Kendall
1989	Geoff Brabham	Nissan GTP ZX-Turbo	Scott Schubot	Pete Halsmer		Bob Leitzinger
1990	Geoff Brabham	Nissan GTP ZX-Turbo	Tomás López Rocha	Dorsey Schroeder		Lance Stewart
1991	Geoff Brabham	Nissan NPT-91	Parker Johnstone	Pete Halsmer		John Fergus
1992	GTP		Lights	GTS	GTO	GTU
	Juan Manuel Fangio II	Toyota Eagle MKIII	Parker Johnstone	Steve Millen	Irv Hoerr	David Loring
1993	Juan Manuel Fangio II	Toyota Eagle MKIII	Parker Johnstone	Tommy Kendall	Charles Morgan	Butch Leitzinger
1994	WSC			GTS	GTO	GTU
	Wayne Taylor	Kudzu-Mazda		Steve Millen	Joe Pezza	Jim Pace
1995	WSC			GTS-1	GTS-2
	Fermín Vélez	Ferrari 333 SP		Irv Hoerr	Jorge Trejos
1996	Wayne Taylor	Riley & Scott-Oldsmobile		Irv Hoerr	Larry Schumacher
1997	WSC			GTS-1	GTS-2	GTS-3
	Butch Leitzinger	Riley & Scott-Ford		Andy Pilgrim	Larry Schumacher	Bill Auberlen
1998	WSC			GT1	GT2	GT3
	Butch Leitzinger	Riley & Scott-Ford		Andy Wallace David Brabham	Larry Schumacher	Mark Simo

See also

• Prototypes: The History of the IMSA GTP Series

References