2003 Chevrolet Corvette Z06 - By Any Other Name...

...Rob Rose's Twin-Turbo C5 Would Be Just As Sweet

Steve Temple Dec 1, 2008 0 Comment(s)
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If you're an engineer, a buildup project typically has a precise timeline from start to finish, with performance benchmarks pacing a tight schedule. Miss any milestones, and you might be out of a job. But when you're talking about a high-velocity Vette, it's not whether you complete it on time, but how fast you can pass by those road markers once it's done.

Rob Rose knows both sides of these equations. Since he's handled all sorts of complex computer projects in his professional life, he's accustomed to staying on schedule. After all, he waited three years to the day for his '03 Z06's warranty to expire before calling a number of turbo companies to improve the car's power output. Even so, his buildup project's timeline stretched out much longer than expected until he reached an 800-plus-horsepower benchmark of performance. (Punctuality wasn't the issue, and really, if you're running a bit late, you can always stomp harder on the go-pedal, right?)

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After shopping around a bit, Rose settled on the STS Turbo Systems kit, which mounts a pair of puffers remotely near the tailpipe, replacing the stock mufflers. He chose the STS unit for two key reasons: space and temperature. "There's not a lot of room under the hood," he points out, "and I didn't want to try to cram a turbo in there. Not only that, it can generate a lot of heat. I've seen turbo housings glow cherry red from running hard on the track, and I didn't want that in the engine bay, melting wires, hoses, or other components."

STS claims a reduction in heat by as much as 500 degrees at the turbos themselves, eliminating the need for a turbo timer to prevent coking on the bearings. In being mounted farther downstream in the exhaust system, the STS unit has a few other advantages as well, such as ease of installation (about a day for a moderately experienced wrench, using standard shop tools). In addition, the rear-mounted turbo acts as a muffler, creating a special sound that is completely different from the typical huffing and rattling of a blow-off valve.

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Other benefits include a cooler intake charge for the engine, due to the inherent intercooling effect of the longer tubing, and the fact that no special headers or other exhaust components are required. (Rose nevertheless added Kooks ceramic-coated 1 7/8-inch headers and a 3-inch midsection.) In addition, the system improves on the front/rear balance by putting more weight near the back end. (Factoring in the poundage removed by the elimination of the factory mufflers, the total increase in weight of an STS system is about 125-150 pounds.)

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But Rose's selection of the STS system was contingent on one thing: The kit had to be street legal. While some Corvette tuners might sneer at that requirement, Rose had good reasons for doing so, and STS principal Rick Squires agreed with them. Getting a CARB E.O. number for an aftermarket power-adder can be a daunting task, but the process was vital to the company's marketing plans for the C5 system.

The first turbo that went on Rose's ride was an air-cooled unit with a conventional journal-bearing setup. The results were impressive. With a dual boost controller, he could dial in anywhere from 5 to 8 psi, good for as much as 558 hp at the wheels (around 657 hp at the flywheel, assuming a 15 -17 percent loss from the driveline).

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Rose promptly headed for the track at Willow Springs, and without breaking a sweat, he trounced both a Mustang and a Mitsubishi Evo (which incidentally ended up running off the track while trying to keep up). He particularly liked the way the STS system maintained boost pressure in the exhaust pipes, so there was little if any turbo lag when accelerating out of the curves.

They say power corrupts, but in the automotive world, it can be fiscally ruinous as well. Many an enthusiast has gotten upside down in a buildup, blindly adding more and more upgrades with no end in sight-at least until the money runs out. But Rose, being a very disciplined guy, stuck to Stage Two of his project plan, which included a pair of bigger turbos.

It began with driving his beloved Z06, now turbocharged, from Southern California to Houston with his 18-year-old son. Once there, he dropped off the car at Motorsport Technologies Inc. to have the stock block swapped out with a custom-built, 402-cube LS2 stroker. While the short-block was already in hand, MTI's technicians had less than a week to get it fully prepped and dressed before Rose's return.

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Components on the custom mill included MTI's Stage II-R heads with ARP studs, Ferrea valves, and dual valvesprings. To keep up with the higher airflow from a new pair of new water-cooled, ball-bearing turbos, MTI installed a set of 60-pound injectors.

Rose went with the bigger ball-bearing pinwheels because they spool up quicker and can handle higher thrust loads. The increased durability is essential for anything over 10 psi of boost, says STS' Squires. He feels water-cooling isn't required, but Rose specified it since he had track duty in mind.

A week later, he flew back to Houston to pick up his car, arriving just in time to see the engine being tested on the dyno. The ensuing experience was a revelation. Running at full boost, the mill churned out 853 rampaging horses at the crank.

"Is this enough?" quipped Jayson Cohen of MTI. Rose's cheeks flushed red with enthusiasm, and he didn't pause to answer in the affirmative.

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Once he got the Vette back home, Rose headed out to the track once again, now armed with a new GM T1 racing suspension and Baer Eradispeed rotors clenched by Hawk race pads.

"The car passes everybody on the straightaways like they're standing still," Rose says. "It's a lot of fun." The downside is a newfound penchant for wheelspin in the turns, which can make things pretty hairy in the corkscrew section at the top of the track, where the pavement goes off-camber over a humped blind curve. It sometimes requires an act of faith to keep on the throttle and fly over it to hit the straight section at full chat.

"You have to watch it," Rose says. "You're pretty much drifting on the corkscrew, but it's still controllable. I've driven crazy fast in it and never spun out." And that's another performance benchmark he intends to preserve.

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