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Callaway Of the Month February '06

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1991 Callaway IMSA Supercar

 

1991 Callaway Twin Turbo IMSA Supercar Series racecar – Owner: The Miller Family

 

This month, we are very pleased to feature the one of a kind Callaway Twin Turbo racecar. Nicknamed, “The Lead Sled”, this car was driven in the IMSA Supercar Series by Boris Said III and was quite fast!

            So fast in fact, the racing sanctioning body determined it must carry additional weight to keep the car in line with other entrants and with the addition of hundreds of pounds of lead ballast, the car became far less competitive in the crowd. The lead is still in place and the car looks much as it did when it raced in 1991.

            Constructed from a 1991 Callaway Twin Turbo, much of the car appears to be the same from the outside. However, under hood and in the cockpit, changes were made for racing. Fitted with data logging equipment, a safety cage and form fitting bucket seats, the car also has communication devices and some other safety gear.

            Due to the nature of the series, the cars were to be kept “stock”. The series rulebook did not allow bodywork modifications and at least one ZR1 was disqualified during a race for having modifications to its spoiler system. The Callaway AeroBody™ was a stock item for 1991 and therefore, it was allowed to race as designed. The term stock however, did not apply when it came to weight. As mentioned earlier, lead ballast was added to this car, bringing the total weight of the car to a burly 3,449 lbs. Approximately 500 lbs more than the true factory weight, by comparison, a factory Porsche turbo entry actually weighed 15 lbs LESS than its street car variant – how's that for competition!

            Bought from Doug Rippie, Chip was approached a couple years later by Doug, who was looking to race the car once again. Chip and Doug drafted an agreement that in retrospect, Lance says was very simple, “just bring it back in one piece”. It was during that attempt at racing that they discovered a reason for the car not being very competitive. The lead ballast was weighing the car down so much that over dips, the car would bottom out, crushing the exhaust. While that is a bad thing to happen for any car, it is terrible for a fire-breathing twin turbo racecar when it came to competing!

After that, Chip got the car back in one piece and then had it freshened and cosmetically refinished. In the pictures below, there is one picture from before the cars' restoration (pictured at the Carlisle grounds). Recently inducted into the Bloomington Gold Hall of Fame, the car is certainly a key piece of Corvette and Callaway history.

© 2006 Chris Chessnoe

 

Callaway IMSA Supercar, Another perspective:

 

Callaway/Doug Rippie Motorsports Corvette: IMSA Bridgestone Potenza Supercar Championship 1990-1992

 

Development

 

The Valley Chevrolet/ Doug Rippie Motorsports Corvettes prepared and campaigned by Doug Rippie, of Plymouth, Minnesota, were a familiar site in the winner’s circle for several years during the highly successful Corvette Challenge of the late 1980’s. Looking for a new challenge, Doug Rippie considers a Callaway Twin Turbo performance upgrade to compete in a new IMSA series that paralleled their previous Corvette Challenge racing efforts.

 

During the winter of 1990-1991 Doug Rippie Motorsports (DRM) and Reeves Callaway conspire to compete with a Callaway Twin Turbo Corvette in the new 1991 IMSA Bridgestone Potenza Supercar Series. At first glance the appearance might suggest that these were showroom stock racecars with no more than a roll cage and safety harnesses. Nothing could be further from the truth. Anticipated competition coming from factory supported Porsches, Lotus, Consulier, Dodge Stealth, Pontiac Firebirds and other racing Corvettes, the Callaway/ DRM IMSA Corvette is fabricated over the winter of 1990 at the DRM complex. With the delivery of the “body in white” (basic Corvette frame without running gear, cowl, floor and rear deck installed), the DRM staff lead by Ken Savare, originally a carpenter by trade before joining the DRM staff rebuilt the chassis with a full competition roll cage. To increase the already stiff Corvette chassis, the roll cage is constructed with 0.095/1.75 inch tubing that connects the tail section of the car through the firewall to the radiator support. For an added measure of safety, all of the factory welds were completed and sealed and a 16-gallon fuel cell is installed.

 

Major changes in suspension geometry were made to maximize the series mandated tire and the newly developed coil-over suspension.  To make the Callaway/ DRM IMSA Corvette as competitive as possible, General Motors (GM) engineers became involved with the overall design of the suspension, design and selection of the shocks, springs and sway bars. The goal was to make the car as competitive as possible with minimal wear on the mandated narrow tires and stock brakes. Not publicly known at the time, Doug Rippie had broad access to the engineering facilities at GM. On one occasion, he recounts driving the Corvette through the office hallway to reach the testing facility because the loading dock was under construction. Once the Callaway/ DRM Corvette was in the super secret GM Vehicle Handling Facility (VHF), the Corvette was placed on a machine that simulated suspension travel under load and track conditions. With this real time information, geometry changes in camber, caster and toe were visible and immediately adjustable. Essentially, the Corvette suspension was thoroughly tested before it ever reached the pavement of a racetrack. As a note, the results of those tests lead GM engineers to make suspension improvements for the up-coming Grand Sport Edition Corvette. Interestingly, the DRM team chose to retain the anti-lock brake system (ABS) as an advantage item. DRM felt that keeping the ABS would be an asset on wet track conditions.

 

Once the chassis dynamics were sorted out and basic fabrication complete, the chassis was sent to Old Lyme, CT for the installation of the finely massaged Callaway Twin Turbo power plant. Once, the drive train was completed by Callaway Advanced Technologies, the necessary peripherals were placed on the bare-chassis, the chassis and a Callaway Aerobody Kit were returned to DRM for body installation. The power output for the Callaway/ DRM Corvette is limited by the rules to 400 hp. Because the rulebook allows balancing and blueprinting of the engine, this is a natural for the Callaway Advanced Technologies motor.

 

Testing

 

To complete an early spring test prior to the start of the IMSA season, the DRM team travels to Arizona’s new Firebird road course for a shakedown run and some track time in their new creation. During the first test run of the Callaway/ DRM Corvette under the Arizona sun, multiple problems were identified, beginning with fuel starvation problems. The DRM team spends two track testing days tracing the problem back to a collapsing fuel line within the fuel tank. Also testing the Bridgestone tires for the first time, the DRM team unfortunately is only able to produce mildly valuable test runs at the very end of the test session due to the time spent with the fuel problem and a new soft track that lacked curbing. The final result is a concern that the Corvette is going to be too heavy and the brakes and tires are not going to last in competition. During the month April 1991, the DRM team is back on the test track, this time at Road Atlanta for the main test of the new series mandated Bridgestone Potenza tire. Final results are successful test runs with few mechanical problems, but still concern over the weight of the racecar leading to brake fad and tire wear. At this point, the DRM crew employs some “creative engineering” to help solve the potential brake problem. Due to excessive heat build-up on heavy braking, the stock aluminum brake caliper would flex and lose grip. DRM modifies the caliper by drilling three parallel shafts through the caliper (3.0 inches by 0.25 inches) and placed stainless steel pins in the shafts. Welding the holes closed on the ends to avoid suspicion, the stainless steel would act as a heat sink and retain its stiffness at a much higher temperature. Likewise, to assist in further heat deflection away from the caliper, a thin sheet of titanium was placed between the caliper and the brake pistons. Similarly, the brake pistons were replaced with stainless steel units.

 

The Series: Short but Sweet

 

For the new IMSA Corvette series, the race format is 30 minutes with no pit stops, no driver changes and series supplies tires. Originally the Birdgestone Potenza tires were a medium-hard compound sized at P275/40ZR17 for the front and P315/35ZR17 in the rear. With a mandated minimum weight of 3814 lbs, the race ready Callaway/ DRM Corvette weighed very close to 3300 lbs, similar to the previous Challenge cars. To reach the new series minimum weight, DRM had to add 500 lbs of lead ballast, combined with fuel and driver the racecar weighed 4100 lbs. far too much for DRM to feel comfortable with the stock braking system and available springs.

 

In the inaugural race of the IMSA Bridgestone Potenza Supercar Series at Lime Rock, CT, the potential of the Callaway/DRM/ Valley Chevrolet Corvette is immediately noticed even though the car was never tested at race speeds. At the very last moment, before the series, the sanctioning body decides to switch the Callaway/ DRM Corvette from the class standard 315 width for the rear tire, to a 295 which was thinner and provided less traction and stopping power. Despite IMSA’s best attempts to slow down Boris Said and the DRM/Callaway Corvette, the car is very competitive. As the third fastest qualifier, behind the pole sitting Consulier and 14th overall, American Boris Said III jumps to the lead after 11 laps. On the 25th lap the Corvette suffers from a right side turbo failure and is retired.  The second race of the season at Watkins Glen, NY the Corvette is again one of the swiftest qualifiers setting second only to the eventual series champion Brumos Porsche of Hurley Haywood. Unfortunately for the Callaway/ DRM/ Valley Chevrolet team, the Corvette is retired again for a right side turbo failure after lap 18. Frustrated with the IMSA sanctioning body and the persistent turbo failure, Doug Rippie and Reeves Callaway decide to discontinue their involvement in the series and the car is sold to Corvette enthusiast Chip Miller. Driver Boris Said III finishes the season 28th in series points.

 

Due to a nearly runaway season by the Brumos Porsche, the 1992 rulebook reflects several key changes to keep the heavier rear wheel drive, non-turbo racecars competitive.  Most significant is a reduction is minimum weight from 3814 to 3400 lbs. Also, new for 1992 is the use of front brake ducting to assist in cooling the stock brake package. As the story goes, Doug Rippie contacts car owner Chip Miller and asks to “borrow” the car because he believes with the 1992 rule changes, the Callaway/ DRM Corvette could once again be competitive.

During the first race of the 1992 season at Lime Rock the Callaway/ DRM Corvette suffers again from a right side turbo failure and scores a DNF. Following the race, the car is being disassembled at the DRM facility and long time friend and founder of Borla Exhaust; Alex Borla notices that the right side exhaust header design seems unsuitable for a racing application. Upon suggestion by Alex Borla, pictures of the right side header are shown to the “God Father” of turbocharged racing engines Alwin Springer of Porsche Racing. Alwin Springer’s review of the design suggested that it would be perfectly fine for a performance streetcar, but for a demanding race environment the design might not be suitable. He commented that the unrestricted path of the exhaust gasses to the turbo allowed the gasses to be traveling too fast at high engine speeds and thereby spinning the turbo on the right side faster than its bearings could tolerate. The problem was never noticed in testing because the car was never run under race conditions for an extended period of time. As the Corvette pushed the performance envelope, the blades of the turbo on the right side would spin too fast for the bearings to manage. The flow of the coolant oil could not keep the bearings cool and they would start to bind. This binding led to a bending of the turbo blades in response to slowing of the turbo shaft against the gas flow. Eventually, the bearing would seize and the turbo blades would break, thus imploding the turbo.

 

According to Doug Rippie, the redesign of the header was a simple repair that could have changed the entire outcome of the first years of the series and the domination by the Brumos Porsche. The car was so competitive in the initial series races; IMSA feared the potential of the car and tried to slow it and Boris Said III down. Unfortunately, the Callaway/ DRM Corvette was never on the right side of lady luck and did not have the chance to display that potential in the winner’s circle.  The Callaway/ Doug Rippie Motorsports Corvette was repainted and returned to the collection of the late Chip Miller where it remains today.

 © 2006 Mike Roberts

©  2005 Callaway Owners Group and their respective authors – all rights reserved.

 Please click on any of the images for a full size version.

   

   

 

 


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