The Dualist

Darren Friedman’s cannily modified C7 Z06 proves its mettle on the street and track

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August 10, 2017

It takes a special car to get the attention of Darren Friedman, who’s no stranger to fast and exciting machines. His ears perked up, however, when in 2014 he read the basic specs for the soon-to-be available ’15 Corvette Z06. The heart of the beast was to be a 6.2-liter, direct-injected LT4 churning out 650 supercharged horsepower. Add in lightweight components, including carbon-fiber roof and hood panels, composite floors and an aluminum space frame; Magnetic Ride Control; electric power steering, the choice of a seven-speed manual or eight-speed automatic transmission; an electronically controlled differential; three different aero packages and a long list of other special features, and the new top Vette promised to combine true supercar performance with unmatched efficiency, civility and longevity. Even better, its starting price of $78,995 undercut the competition by tens of thousands of dollars.

Friedman’s approach to life in general, and cars in particular, is summed up by one of his favorite quotes, which holds that “It’s better to be a racer for a moment than a spectator for a lifetime.” This credo led him to establish Speed Limit Racing, a business that provides a safe and structured environment to promote driving skills through a variety of programs, including driver-education classes, autocrosses and track days. The C7 Z06 was thus tailor made for Friedman, and there was never any doubt about what he’d do with his when it arrived.

Not surprisingly, Friedman specified the Z07 Performance Package for his Z06. This option transforms an already ferocious car into the most track-capable Corvette Chevy has ever produced. The package includes larger end plates for the front splitter, an adjustable transparent “wickerbill” on the rear spoiler, unique suspension tuning, Brembo carbon-ceramic brake rotors (sized at 15.6 inches up front and 15.3 inches in the rear) and summer-only Michelin Pilot Sport Cup 2 ZP tires. Friedman patiently waited for his car to come in, and the moment the dealer called, he was ready to roll. “After receiving my Z06 in May of 2015,” he explains, “I immediately put on the required 500 break-in miles, changed the oil and then headed straight to the track.”

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To paraphrase what the Hair Club for Men’s Sy Sperling used to say in his cheesy 1980s TV commercials, Friedman is not only the Speed Limit Racing president, he’s also a client. In fact, he may well be his own most active client, with more than 150 track events on his résumé. “And that number is growing,” he tells us, “because I’m doing at least three or four events per month, every month, all over California and in neighboring states.”

Friedman has done track days with a wide variety of vehicles over the years, and in addition to his Corvette, he currently competes in a Porsche Cayman GT4, a BMW M3, a Porsche 911 Turbo S and a Kirkham 427 Cobra. So how does the Z06 stack up? “My first impression was that [it offered] a great bang for the buck. Then the reality hit that it doesn’t like spirited driving in the heat. After I completed two or three fast laps, overheating issues set in and caused the dreaded ‘limp mode.’ I had to do something.”

The “something” that Friedman chose to do was neither minor nor cheap, but the results were practically guaranteed: He shipped the hot-running Corvette off to Callaway Cars’ West Coast facility in Temecula, California for a complete SC757 conversion. “The overheating problem was what got me thinking about Callaway to begin with,” he remembers, “but that was only part of it. From doing so much competition over time, my skill level had increased to the point where I wanted the car to be faster, and the SC757 package [would be] a huge help with that as well.”

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The raw meat of the conversion consists of Callaway’s GenThree TVS2300 supercharger and TripleCooled intercooler system, along with a high-flow intake setup whose runners are designed to increase mid-range torque. The GenThree blower was designed in-house by Callaway’s own engineers, with a focus on reducing charge-air temperatures and increasing flow. With Callaway’s previous superchargers (and those of most other manufacturers as well), the compressed air is channeled through a single liquid-to-air intercooler and then downward into a log-style manifold shared by all cylinders. With the new design, engineers rotated the supercharger’s rotor-pack assembly 180 degrees to route the air up rather than down. It then goes through a primary intercooler and around the sides of the housing. The intercooler’s fluid circulates through a heat exchanger positioned in front of the car’s radiator.

Following its trip through the primary intercooler, the air flows through the upper section of the supercharger’s housing. Because the housing extends through an opening in the hood, and is thus smothered in ambient air, it further cools the incoming charge via convective transfer. Finally, the air charge passes through two more intercoolers (one for each cylinder bank) for additional heat extraction before heading into the combustion chambers.

According to Callaway, this clever design yields an inlet-air temperature increase of less than 10 degrees (F), a huge improvement over conventional setups, which typically increase those temps by at least 35 degrees. This reduction helps avoid the “heat soak” phenomenon to which all supercharged track cars are prone.

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The Callaway TVS2300 is manufactured using an Eaton 2300cc TVS rotor pack that is 32 percent larger than a stock Z06’s 1740cc unit. That larger size applies to the outside as well as the inside, prohibiting the installation of the GenThree system under a Corvette’s stock hood. Callaway solved this problem, while also enhancing cooling, by allowing the supercharger’s housing to protrude through a “window” in the hood.

The Callaway SC757 package increases the LT4’s factory output from 650 horsepower and 650 pound-feet of torque to, as the name implies, 757 hp and 777 lb-ft. According to Callaway, an SC757 will rocket from 0 to 60 mph in about 2.8 seconds and turn the standing quarter-mile in 10.5 seconds at 131 mph. Although we can’t confirm those claims, our recent, bracing experience with an SC757-powered AeroWagen (“Shooting Star,” September 2017) gave us no reason to doubt them. (For reference, Chevy claims that a stock Z06 will reach 60 mph from naught in about 3 seconds and cover the quarter in 11.4 ticks at 127.)

While Callaway’s innovative supercharger design and careful attention to air-charge cooling help a great deal, Friedman wanted to further ensure that his car­—which he drives on the street almost daily—wouldn’t have any overheating problems on even the hottest California summer days. To that end, he chose to install an LG Motorsports Super Cool Track Package. “The overheating issue has been a real problem for a lot of Z06 owners, and I was determined to overcome it,” he explains. “I consulted with Donny Yorke, who is a master Chevrolet mechanic, all-around Corvette expert and responsible for all aspects of racecar preparation at Speed Limit Racing. We determined that the LG system was the best available, and Donny did the complete installation.”

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Rather than simply being a collection of new parts, the Super Cool Track Package is a complete, engineered system. It relocates the factory transmission cooler from the front of the car to the rear and pairs it with an additional cooler. The stock engine intercoolers are replaced with LG 12 Super Cooler units mounted in the areas ahead of each front wheel. Large, screen-covered openings in the front fascia feed outside air to these intercoolers, while wind-tunnel-tested louvers in the inner wheel wells route the air out. An upgraded fan kit and radiator round out this comprehensive cooling-system makeover.

LG Motorsports is based in Texas, so it had no trouble testing the setup in extreme circumstances. The company claims that, even running full bore on a track in 100-plus degrees, the Super Cool Track Package kept its test Z06 from overheating. Friedman’s experience has validated this. “I run in a wide variety of very demanding circumstances, from autocrosses and tight tracks to high-speed circuits such as Fontana, where I’m [running at] over 165 mph for lap after lap, and none of my temperatures are high,” he reports. “In fact, everything—including engine coolant, engine oil, transmission fluid and diff oil—gets up to normal operating temperature and stays there, even on the hottest days.”

With his overheating problem solved, and 757 hp on tap, Friedman is delighted with his Z06. “It’s everything I want it to be and more. Among other things, I run the Wilwood Corvette Challenge in the Ultimate Class [he’s currently leading in the championship-points chase], so I compete against some hardcore racers with stripped-down cars running giant wings and so on. This car, with its full interior and cold air conditioning, is competitive with all of them. The Z06 is a fantastic machine to begin with, and the Callaway package truly turns it into a street-legal racecar.”

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Also from Issue 116

  • Modernized C1 Fuelie
  • C6 Buyer's Guide
  • Restored '75 Driver
  • Guldstrand Nassau Roadster
  • LS3 '62 Restomod
  • Racing: Prepping for Le Mans
  • Vette-Powered Cheetah Racer
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