While some can only dream of owning a $70,000 supercar such as the LS7-powered Corvette Z06, some followed their purchase with envy of the new ZR1's output and the means to do something about it. Thankfully the Australian company Air Power Systems (APS) makes a twin-turbo kit with OEM-quality fit and finish that will transform the already potent 427-cube Gen IV into a fire-breathing dragon, and satisfy even the most hard-to-please Corvette owner. With their recent release to the U.S. market and a limited amount of U.S. retailers and distributors, we had only seen a few installed kits on GTOs and F-bodies. All seemed to look and perform marvelously, though, with one of the most complete, well thought out, and high-quality designs out there. When we happened to get wind of an upcoming install at APS retailer and installer Redline Motorsports in Schenectady, NY, I jumped at the chance to get this exciting new product onto the pages of GMHTP and Editor Jensen was happy to comply.
Like all of its late model GM kits, the APS C6 Z06 Twin Turbo Kit comes with two cutting edge Garrett water-cooled turbos, heavy-duty cast manifolds, high efficiency bar and plate air-to-air intercoolers, hot and cold plumbing, a higher capacity MAF housing, twin APS blow-off valves, and TiAl wastegates. For the hungry 427 LS7, APS supplies Garrett GT3582R ball bearing turbos with Inconel turbine wheels that efficiently produce up to 1200 horses at only 18psi knowing that with a few modifications-such as forged pistons-these engines can certainly handle it. Big turbos, though, need big wastegates, so cleverly packaged TiAl 44mm units are tucked under the floor pan. This particular kit also comes with a larger oil cooler (to replace the smaller factory piece), a stainless steel after-cat exhaust, and the necessary fuel system upgrades including high flow fuel rails, injectors, and dual in-tank pumps.
Our '06 test car is Redline's official guinea pig, which owner Howard Tanner had previously had a set of Kooks long-tube headers, B&B exhaust, and a centrifugal blower enhancing the stock motor. He had planned to use the APS kit to eventually make up to 1,000 rear wheel horsepower, so the first order of business was to replace the stock LS7 with a low compression 427 using Diamond forged pistons, as well as a heavy-duty set of rods and a crank, and a re-sleeved block from Race Engine Development. He even decided to have West Coast Cylinder Heads port a set of LS7 heads and put in a larger boost cam. That being said, we expected that even at 6psi dyno pulls would be healthier than a boosted stock LS7. (APS claims 625 horses at the wheels in that configuration.) The added benefit of having the fortified motor is that Howard had no problem cranking up the boost to 9psi on pump gas to give us an idea of what this kit was really capable of, where the stock hypereutectic pistons and lightweight titanium rods might have called it quits.
In addition to installing the APS kit as it has on many C6s, Redline will also be doing a custom tune on the E38 computer. On higher horsepower, boosted applications, the ZO6's ECM has proven quite limited when it comes to fueling control with larger injectors (needed to feed these power levels), according to Howard, Redline's proprietor and expert tuner. With a bone stock motor and 6psi, no issues were to be expected. However, with the modified motor and increased boost we could only hope that the higher capacity APS MAF housing would be able to keep up, or a Speed Density tune would most likely be the only alternative. The E38 PCM has a hard limit of 12,200 Hz, which is the max value the MAF can report. Once this value has been exceeded, the MAF is considered to be "pegged" and the PCM does not know how much air is entering the motor. The larger MAF housing slows down the air signal and provides more range as the result. Either way, Howard was happy to make good use of EFILive, which he says is head and shoulders above any other tuning software for tuning the LS7s due to its "Virtual VE Table" and easy to read data logging features. For initial wide-open throttle tuning and testing of the kit, Redline would also be employing its brand new digital Dyno Dynamics DS450 and high-speed wideband O2. Further tuning would be done on the street, where the ZO6 feels most at home. Though the C6 still has a stock driveline save the RAM dual disc clutch, billet slave, and LG Motorsports carbon fiber driveshaft, we had also hoped to get some track times out of this beast-though the 3200-pound coupe would have little chance of hooking.
EFILive tuning software was used to tune the beast using its unique "Virtual VE Table" function, as the E38 computer uses complex algorithms instead of an actual VE table which we are used to. After starting with the stock tune, 150rpm and ignition timing is added to smooth the idle, and the fuel is trimmed for the bigger injectors. Normally idle parameters wouldn't of had to be modified but the larger camshaft required these changes. Howard made some initial pulls with the 6psi wastegate springs and dialed in the tune. At 9psi, he starts with 12.5 to 14.0 degrees of timing at WOT, which he says is close to APS's tune. Another 3-4 degrees of timing is added from 1600-1800rpm before boost kicks in. Another 2 degrees is added at the upper end by the final tune. Howard says a good rule of thumb is to back off timing at peak torque then ramp back up again. Each pull was data logged with the wideband O2 wired in to make corrections easier. Air/fuel stayed around 11.7 to 12.0 with the final tune, and thankfully there was still some headroom with APS's MAF as it hit only 10,300 Hz. No need for Speed Density just yet.
Logically, the 3psi jump in boost provides a linear increase in power especially from full boost to the over 6500rpm max. As impressive as 654 and 760 peak horsepower sounds, it's not nearly as remarkable as the 600 and 700 ft-lbs of torque available from 3500rpm to 5500rpm. Peak torque numbers were 614 and 730 lb-ft respectively. The incredibly flat torque curve gives a seat-of-the-pants feel comparable to a much more powerful car. The first three gears appear nearly useless with more than a light brush of the throttle. For comparison, a stock ZO6 recently baselined at 450hp and 420 lb-ft on Redline's dyno.
The substantial TiAl wastegates proved steady and reliable, even at 9psi. The increased boost caused only a couple hundred rpm increase in lag, but a much more violent initial hit to the Dyno Dynamics rollers.
Even with a set of M&H 26x12 slicks and skinnies mounted on 16-inch CCW wheels, the turbocharged LS7 still couldn't hold traction on E-town's super-glued launch pad. Almost as soon as boost hit the ZO6 wanted to immediately pitch sideways. One observer stated succinctly, "that car is just evil." After quite a few tries, tire pressure was set at 18psi and Howard walked it out of the hole, making it to the 60-foot in 1.94 seconds. Once he had quite a bit of forward momentum, he was finally able to squeeze into full throttle in second gear. As the result, the 10.68 ET was achieved at 141.3 mph. Most drag racing calculators would attribute that speed worthy of an ET a full second faster. Despite the difficulties hooking, Redline certainly gave us a taste of this kit's awesome potential.