thebeginningoftheimsagtpera.

The beginning of the IMSA GTP era.

Selected photographs taken in 1981 at the Mid-Ohio Spots Car Course that illustrate a time of transition in spots car racing.

In 1981 a new breed of car had made its way on to the North American road racing scene. Running in racing events sanctioned by the International Motor Sports Association, otherwise known as IMSA, a racing class designated as Grand Touring Prototype, or GTP, had just been established by the organization.

IMSA GTP racing cars were completely purpose-built machines having no commonality with road going cars, with the possible exception of their basic engine layout. They featured enclosed cockpits, including a driver's seat and space for at least a theoretical passenger seat. Initially, GTP machines closely resembled cars that were to run in the international Group C prototype category, but the North American based racers were built to meet a number of fundamental rule-driven design differences over their globe trekking cousins. Over the course of the essentially parallel GTP/Group C era design specifications for the machines competing in either classification would increasingly merge together. The IMSA GTP era came to an end in late 1993, the last race for the classification having been run in October of that year.

In 1981 IMSA races included cars in the GTP category as well as those in the GTX, or Grand Touring Experimental category. GTP would eventually eclipse and replace GTX as IMSA's premier racing class, but this was allowed to happen in phases. GTX machines were those that to some degree were to resemble the road going car upon which they were based. During the pinnacle of GTX racing car development the idea of resemblance was pushed to the limit. About all the commonality some of the machines shared with their road-going counterparts was their roof line.

Again with some technical differences, IMSA GTX cars closely resembled those racing in the international Group 5 category. As opposed to the early GTP - Group C design conflict it was possible to run the same car in both the GTX and Group 5 categories by specifically configuring the machine for either class, however.

IMSA filled out their Grand Touring racing field with cars running in two other classes. The GTO class encompassed stock appearing, race modified Grand Touring cars with engines over 2.5 liters in displacement (thus the "O" in GTO) and the GTU class featured stock appearing, race modified Grand Touring machines sporting engines under 2.5 liters in displacement (thus the "U" in GTU). During the period of time that both the GTP and GTX classes coexisted this meant cars running in four distinct racing classes with a wide range of performance capabilities shared the track with each other during almost any given race, leading to some very interesting moments at times. All the cars in all of these Grand Touring classes were campaigned under the banner of the IMSA GT Championship.

In. late May of 1981 the IMSA racing tour visited the Mid-Ohio Sports Car Course near Lexington, Ohio. Below are some scanned photographs from that event which help illustrate the beginning of the GTP era described above.

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Above is a 1981 March - BMW M1/C Grand Touring Prototype (GTP) racer being prepared in Mid Ohio's paddock area. The car itself, or chassis as it's known in road racing circles, was constructed by the March Engineering race car building firm in England. Auto manufacturer BMW of Germany supplied fully race prepared engines for the machine in a collaboration with March, thus the March - BMW designation. This vehicle may also be known as a March 81/P BMW, which would be more in following with March Engineering's standard method of chassis designation.

Another view of the March - BMW M1/C being made ready for its race. One might notice the car sitting on nothing but grass in this scene. This event took place a year or so before a great many improvements were made to the Mid Ohio facilities by Jim Trueman. founder of the Red Roof Inns motel chain, who purchased the track in the fall of 1981. Among the improvements implemented by the late Mr. Trueman were modernized and expanded garage facilities as well as paving of much of the paddock area. It would be quite remarkable in current times to see a major entrant of a major racing series (such as the Kenwood Stereo March/BMW team) preparing their car in the middle of a grassy field, just as the lowest budget amateur sports car racing team might, but that's the way things were in 1981.

The March - BMW M1/C on track, driven by international racing standout David Hobbs. Despite some teething problems the M1/C was capable of great performance. As an aside, BMW would power the Brabham Formula One team to a championship later in the `80s during F1's "turbo era", producing staggering horsepower from their four cylinder turbo charged Grand Prix engines.

The Cooke Woods Racing T600 from Lola Racing Cars. The ever popular and proven driver of England was this car's primary pilot. With its mechanically fuel-injected, competition built small block Chevy V-8 providing power Lola had this prototype car a winner almost out of the crate. The T600 would set the goal for early GTP racers. As pictured above, with its front bodywork removed, one might notice one of the front on-board pneumatic jacks supporting the T600. This racer also finding itself being made ready on a grassy spot in the paddock, the plywood under the car was necessary to provide a base for the front air jacks.

More plywood covering the grass, this time with rigid jack stands holding the rear of the T600 in the air. The rear wing and wing support structure are fairly clear in the above photo. What isn't so evident is the under car aerodynamic shaping used on this Lola. The at-the-time relatively new concept of "ground effect" aerodynamics, in which tunnels of a sort that begin with a small cross section at the front (inlet) and increase to a much larger cross section at the rear (outlet) are incorporated between the car's wheelbase, was finding its way in to an increasing variety of racing categories. As the race car moves through the surrounding air these tunnels couple with the roadway beneath them to create a venturi effect which produces a low air pressure area within the tunnel, causing the higher pressure air surrounding the tunnels to push them, and thus the car, down to the roadway. The T600 made use of an early application of of this technology.

Brian Redman and the T600 on track, driving through what appear to be "the esses" at Mid-Ohio. Redman is pictured here driving around a Porsche 935 GTX car with a Mazda RX-7 GTU machine behind them both.

Switching from the newest thing at the time (GTP cars) to the tried and true (the GTX class), above is Chris Cord'sChevrolet Monza GTX racing machine being made ready. A number of Monzas found their way in to both IMSA GTX and Group 5 racing levels. As with other GTX cars, the Monzas were highly modified and shared little commonality with their road going counterparts. A GTX Monza, such as the one pictured above, could be spectacular to see and hear in competition with its high horsepower racing-prepped Chevy V-8.

Chris Cord's GTX Monza on track. If one looks very closely at the above photo the highly exaggerated front and rear flared fenders on the car may be apparent. These were commonly known as IMSA flares and the parts needed to add them to a Chevrolet Monza were available through the General Motors Parts Division and assigned actual GM part numbers (meant for off-highway use, of course).

Above is pictured a Porsche 935 GTX machine entered by J.L.P. (John L. Paul) Racing with its front fenders temporarily removed. The ultimate basis for Porsche's model 935 race car can be found in their venerable 911 road car. While many Porsche 911s have been converted from road going touring cars to full-fledged racers, 935s were built strictly for the track. The 935 was a racing car built by Porsche, just as they build their road going cars, and evolved over its production life in to a number of variants. Several years after Porsche halted continued development of the racing machine a number of outside tuning firms continued to advance the car's design.

Rear view of the J.L.P. Racing 935. Just as the Porsche 911 road car, a horizontally opposed, air cooled six cylinder "boxer" engine finds its home at the rear of the 935. Technically inclined page viewers may notice twin-turbochargers at the very rear of the car. The use of twin-turbocharges was allowed under GTX regulations where the international Group 5 classification allowed the cars to run only a single turbocharger. Employing twin-turbochargers was advantageous over the use of a single turbo for multiple reasons (one being lighter rotating mass in each smaller twin-turbo vs. a larger single single allowed for quicker "spool-up" time in the case of the twins).

A crew member warming up Ted Field's Interscope Racing Porsche 935. 935s had idle characteristics more akin to a high performance road car than an all-out racer. On track, however, there was no mistaking the fact they were built for nothing but competition. As a point of interest, Ted Field is a member of the Field family of Chicago retailing fame as well as the founder of Interscope Communications and Interscope Records. He not only owned the Interscope Racing team, but served as one of its drivers at IMSA events as well, being a co-driver of the 935 pictured above.

The Interscope Racing Porsche 935 on track. Ted Field and Bill Whittington were the drivers of this car, with a driver change occurring in mid race -- which was typical for IMSA GT events. Several facets of IMSA GT made it a fairly unique racing series, one of which being the fact that many of the team owners in the series were successful business people who also drove their cars along side hired professional racers. Many of these business people became talented racers in their own right, such as Ted Field.

The "Moby Dick" Porsche 935 of Dr. Gianpiero Moretti's Momo Racing about to overtake a Mazda RX-7 GTU car. Dr. Moretti, founder of the Momo manufacturing firm in Italy, is another example of a successful business person turned accomplished racing driver. This 935 is referred to as the Moby Dick type due to its extended tail section resembling that of a whale, initially designed to provide aerodynamic stability on extended high speed sections of race track, such as the Mulsanne Straight at the Le Mans racing circuit. Dr. Moretti's Moby Dick 935 exemplifies the fact that many variations of the Porsche model were produced over its competitive life span. The 935 came to be the dominant type in both IMSA GTX and international Group 5 racing.

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While only two IMSA GTP cars are pictured above, a wide variety of designs made their way on to the racing circuit over the life of the GTP era. During the peak of the IMSA GT series, probably from the mid to late 1980s, prototype racers were built and entered by a variety of racing car manufacturers as well as major auto makers, such as Jaguar, Nissan, Toyota, Pontiac, Chevrolet and Ford. The most dominating GTP design, though, was the Porsche 962. Initially paired with a cousin specifically built for Group C racing, the Porsche 956, the 962 carried on the 935's legacy of great success in both IMSA GTP and eventually Group C racing as well.

A new, reorganized International Motor Sports Association lives on to this day and may be found online at IMSA - International Motor Sports Association . The current iteration of IMSA sanctions a number of racing series, one of which being the American Le Mans Series, or ALMS. In North America the ALMS provides a modern-day approximation of the old IMSA GT Series described in the above story. The American Le Mans Series may be found online at: http://www.americanlemans.com

All photos on this page by DFH

March, 2009

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