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1991 Chevy Corvette ZR-1 - Purple Streak

Robert DeMarco’s ZR-1 exemplifies the golden era of C4 performance tuning

Christopher R. Phillip Dec 10, 2013
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Robert DeMarco, an energy-service specialist from Frankenmuth, Michigan, counts himself among the most passionate of late-model-Corvette owners. He’s a member of the ZR-1 Registry, the Pace Car Registry, the Grand Sport Registry, and the National Corvette Museum. He owns a 1991 Shinoda ZR-1, a 1993 Callaway 40th Anniversary ZR-1, and a 1998 Pace Car. However, it may just be his latest acquisition—a Purple Pearl Mist 1991 ZR-1 with a Callaway Aerobody kit and a Doug Rippie Motorsports DRM 500 engine conversion—that amplifies his affection for America’s Favorite Sports Car like no other.


His royal-colored Corvette’s saga starts with second owner Jim Caldwell, who decreed that the majesty of his pre-owned “King of the Hill” ZR-1 was simply the starting line for more potential. Inspired by the bright-purple Callaway CR-1 Corvette on the front cover of the Feb. 1993 issue of Road and Track, he resolved that his Steel Blue stocker needed to lift some significant DNA from the Old Lyme, Connecticut, tuner’s one-off supercar.

His first stop was Corvette Connection in Denver, Colorado, in January 1993, where shop owner Rich Lenhart and his techs installed a Callaway Aerobody kit. The package included a one-piece fiberglass front bumper with integrated turn-signal lenses and hood-emblem relocation, Callaway “teardrop” hood bulges, side fenders with Aero Gills, lower-rocker flare extensions, door-skin overlays, lower-rear-quarter Aero Gills, a one-piece fiberglass rear bumper, and bubble taillamp lenses.


Assorted previous owners added more than $40,000 in mods to this ZR-1 before Robert DeMarco purchased it in 2011.

The shop’s painters then sprayed an interpretation of the Callaway cover car’s exterior hue onto the Corvette’s body. “It was truly Jim’s vision for his ZR-1,” Lenhart says.

In April 1995, Caldwell dispatched his ZR-1 to Doug Rippie Motorsports (DRM) in Buffalo, Minnesota, where owner Rippie and his team upped the LT5 engine’s brawn from 375 to 475 hp. The transformation included DRM custom camshafts (the LT5 has four); CNC-ported cylinder heads, plenum, and injector housings; a 63mm throttle body; a modified air-filter lid and K&N air filter; and custom ECM calibration.

“We wanted a high-horsepower package that was 50-state legal, and that forced us to retain the factory exhaust manifolds,” Rippie recalls. “With GM’s permission, we sent LT5 heads, plenum, and injector housings to their manufacturer, Mercruiser for the same race-porting package they were delivering to professional Corvette teams like [Tommy] Morrison and [Kim] Baker. GM also allowed us to work with Engine Power Components in Grand Haven, Michigan, which ground the camshafts for the LT5 engines. EPC worked with us to develop our proprietary cam, which shared the same primary profiles as the factory units, but [had] more-aggressive secondaries with higher duration and lift.”


Originally rated at 375 hp, this LT5 now makes around 500 horses at the flywheel, thanks to a battery of well-executed upgrades.

Rippie says he also installed one of his signature Quick Quarter suspensions onto Caldwell’s ZR-1. The conversion entailed swapping out the factory trailing-arm brackets for custom units that offered a better launch off the starting line. Custom camber brackets, meanwhile, minimize the amount of camber change on the rear wheels.

Later that year, Caldwell enlisted Auto Master of Palm Desert, California, for even more speed mods: a Fidanza lightweight flywheel, a Carolina Clutch and Performance Stage 2 clutch, a Ron Davis aluminum radiator, E10-ethanol-compatible injectors, and a Dana Super 44 limited-slip differential stuffed with 4.09 gears.

In 2000 he sold his ZR-1 to Clint Hooper, who added Callaway-style O.Z Racing Mito wheels before he, too, sold the car in 2002.

The Vette passed through several more owners over the next four years, eventually ending up in Mark Sidwell’s collection in Rome, Georgia, in 2006. “The factory transmission was making a noise, so one of the first things I did was have a new-old-stock ZF six-speed and aftermarket short-throw shifter installed by Corvette Country in Fairburn, Georgia,” he says.


Sometime later, he enlisted the expertise of Aaron Scott of South Georgia Corvettes in Thomasville, Georgia, who performed additional porting on the heads and port-matched them to Watson long-tube headers, which he installed along with a B&B Tri-Flo exhaust. “It made the ZR-1 sound pretty aggressive,” Sidwell says.

In 2010 he sold the car to Calvin Smith, a Corvette collector in Charlotte, North Carolina.

That brings us back to this ZR-1’s current owner. “I first saw [this Vette] on an Internet forum in May 2011, where members discussed seeing it in an online auction with a buy-it-now price of $28,000,” DeMarco says. “I contacted Smith, but to my disappointment he told me that he was reserving it for a potential buyer.


“I wanted it so badly that I called him every day for two weeks straight to check the deal’s status,” he continues. “On day 14, he told me, ‘I’ll give him one more day, or you can buy it if you want it.’ Twenty-four hours later, I called him again, learned the other buyer had not responded, and bought the car sight unseen.”

Since then, DeMarco has bolted up Baer EradiSpeed drilled-and-slotted rotors. He also had Mark Haibeck of ZR-1 Specialist in Addison, Illinois, install Quick Time Performance’s Electric Cutout (QTEC), custom-tune the ECM, and strap the ZR-1 on a chassis dyno, where it opened up and roared to the tune of a respectable 421 hp/389 lb-ft at the rear wheels.

Now with only 35,000 miles on its odometer, this unique-colored ZR-1 really enjoys its royal life. “Since my wife and I have daily-driver Corvettes, we use it to travel and attend car shows. To date, it’s won Concours honors and Top 30—out of 5,000-plus competitors—at Flint, Michigan’s Back to the Bricks, in 2011,” he says.


So what does the future hold for this King of the Hill?

“I plan on installing custom twin turbos set to four pounds of boost, and repurposing the front-fender Air Gills to draw air into the impellers,” DeMarco says. “Since the factory LT5 ECM was never designed for such a modification, I’ll also install one of the new aftermarket LT5 ECMs being produced by Megasquirt. I anticipate the upgrade will produce 580-plus horsepower at the rear wheels”

At that level, DeMarco’s ZR-1 will give brand-new Corvettes a lesson in royal sovereignty. After all, once a king, always a king.


Paul Deutschman–penned Aerobody kit included rear-quarter Aero Gills and bubble-style rear taillamps, among other modifications.

Spec Sheet

1991 ZR-1

Owners Amy and Robert DeMarco; Frankenmuth, MI
Block LT5 Aluminum
Displacement 350 ci
Compression Ratio 11:1
Heads 32-valve LT5 aluminum, ported by Doug Rippie Motorsports (DRM) and South Georgia Corvettes
Valves Stock 1.54-/1.39-in
Camshafts Custom DRM with stock primary (approx. 214-deg duration, 0.229-/0.214-in lift) and custom secondary lobes (approx. 230-/230-deg duration, 0.390-/0.390-in lift, 110-/114-deg LSA)
Crankshaft Stock nitrided forged steel
Rods Stock forged steel
Pistons Stock cast aluminum
Intake Manifold Stock with ported housing and plenum
Throttle Body DRM 63mm
Fuel Injectors RC Engineering
Fuel Pump Stock
Ignition Stock
Exhaust System Watson long-tube headers with 2-in primaries, B&B Tri-Flo exhaust (first-generation), Quick Time Performance electric cutouts
Transmission ZF six-speed manual
Clutch Carolina Stage II clutch, Fidanza lightweight flywheel
Driveshaft T-6 aluminum by Denny’s Driveshaft
Front Suspension DRM coilovers (Bilstein shocks, Hyperco springs, DRM custom spring rates and valving)
Rear Suspension DRM coilovers (Bilstein shocks, Hyperco springs, DRM custom spring rates and valving), DRM Quick Quarter package
Rear End Super Dana 44 with 4.09 gears
Front Brakes Baer EradiSpeed 13-in drilled/slotted discs, stock calipers
Rear Brakes Baer EradiSpeed 12-in drilled/slotted discs, stock calipers
Wheels O.Z. Mito; 18x10 (front), 18x12 (rear)
Front Tires Goodyear Supercar 285/40ZR18
Rear Tires Mickey Thompson 345/35-18 E.T. Street
Fuel Octane 93
Weight 3,939 lbs with driver
Best E.T./MPH 11.99/116
Best 60-ft. Time 1.89
Current Mileage 35,000
Miles Driven Weekly Less than 50



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