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2008 Corvette Z51 - Queens Garage

Homebuilt Single Turbo C6 That Makes Over 1,000 RWHP in Street Trim

Richard Prince May 3, 2012
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Let's face it, the Corvette engineers did not waste any space on the C6 chassis. So trying to retrofit a turbocharger system is no easy task, which leads many to forgo the traditional single turbo and go right for a low-mounted twin setup to conserve space. In fact, many have said that a single turbo setup on a streetcar is pretty well impossible. The same people would probably say that building a 1,000-rear wheel horsepower C6 out of your two-car garage is also impossible. But since when have New Yorkers gave a damn what anyone else thinks?

Louis Pepe is a 26-year-old restaurant manager from Queens, Middle Village to be specific, and his best friend, Matthew Pospishil, is from just up the road (in Glendale). The two have spent many hours in Louis' garage on past projects, whether it was Louis' '00 WS6 with a 76mm hairdryer or Matthew's own Z28 equipped with an 88m unit. Though Louis has been through a total of five previous engine setups on his 2008 C6 Z51, clearly both him and Matthew are partial to turbochargers. After the timing chain broke on his blown, 418 stroker, he let Matthew talk him into fabricating a single turbo kit from scratch while they were rebuilding. Some may cringe at the thought of tearing apart a 4-year old Corvette, but Louis didn't wait long to put on some long-tube headers and a cam after purchasing the car brand-new – so what's a couple of holes?

Also with help from Chris Jurkowitsch, Louis and Matthew pulled the broken 418 and sent it out for a rebuild at LAB Engines in nearby Lindenhurst. A Callies Compstar crankshaft would continue to provide 4-inches of stroke to the over-square motor with help from Compstar H-beam rods and Wiseco -32cc dished pistons. When mated back to CNC-ported LS3 heads built by Frankie Ford with Ferrea valves, the LS3 had a boost and pump gas friendly 8.7:1 compression. Yella Terra 1.8 ratio rocker arms command the stock sized valves at the instruction of a turbo-friendly, symmetric hydraulic roller from Comp Cams with 224-degrees of duration and .624-inch of lift, cut on a 118 lobe separation angle. A ported stock oil pump keeps the motor lubricated. Meanwhile the engine is topped off with a stock LS3 intake manifold and a ported stock throttle body.

The fresh bullet was dropped back into the C6 chassis where Matthew got to work at mapping out the turbo kit. First thing was first; the air conditioning compressor would have to go in order to make room. Second, the water pump neck had to be changed to a right angle for additional clearance. And last, the radiator was pushed back to be flush against the frame rail (instead of leaned back). This provided enough room for Matthew to fabricate the 2-inch primary headers, a 2.5-inch crossover and 4-inch downpipe using stainless steel from American Racing Headers to feed a Forced Inductions GT-91 turbo. A JGS 60mm wastegate was used to regulate boost, and a JGS blow-off valve prevents surge on the 3-inch V-banded aluminum cold side. A hole was cut in the fender to funnel the turbo's discharge into a CX Racing air-to-air intercooler mounted just behind the bumper, which is also aided by the use of E85 fuel exclusively–supplied by both the factory pump and a Fuelab external pump.

In addition to the welding and fabricating, Matthew was also the man behind the keyboard – providing a custom speed density tune. The MAF was deemed insufficient for keeping up with the fresh air being sucked through the 5-inch K&N filter by the 91mm compressor. The Garrett-based turbocharger also required some massive 120-pound injectors to spray enough E85 to keep up with the fueling demands. On their first dyno attempt at only 15psi this combo made a stout 900 horsepower and 842 lb-ft at the wheels. With just an additional 3psi, as the turbo is climbing into its efficiency range, and tuning, the 418 reached the vaunted four-digit threshold. Though 1,068 hp is more than enough for any streetcar, Louis has talked about turning up the boost. The turbo kit can clearly support it, but we have to wonder whether this is one of those times when you should leave well enough alone (or maybe I'm just getting old!).

Perhaps a testament to the Corvette and GM Powertrain engineers, a great deal of Louis' drivetrain and suspension is stock. A SPEC Super Twin clutch and steel flywheel as well as a DTE trans brace are the only upgrades to the transaxle. Even the shifter is stock on his TR6060. Meanwhile all of the factory Z51 sway bars, shocks and composite leaf springs are also intact for a comfortable ride. With a sticky set of Mickey Thompson 345mm drag radials and M&H skinnies mounted on a CCW drag pack, we expect some impressive track numbers from the C6 in the future, but for now Louis enjoys getting a sense for its seemingly endless power supply on the street – counter-steering required.

In the mean time, Louis plans to add a roll bar to the mostly stock interior. Gauges have been mounted in the middle air vents thanks to a bezel from Double D Mods. The exterior is also a mix of subtle yet very functional and effective upgrades including the Z06 quarter panels that allow such meaty rear tires, Z06 spoiler, ACI front splitter, and the icing on the cake – an RK Sport Violater carbon fiber hood. All body work and color-matching to the factory Jetstream Blue was farmed out to the experts at Sands Point Autobody in Port Washington.

Louis credits his friends Matthew and Chris, who each have pretty potent rides of their own, for putting together his C6 as well as the support of his family. Of course a little help from the professionals is always necessary, but all three should be very proud of what they have accomplished. It truly is amazing what a few guys from Queens can do in a simple two-car garage.

Though 1,068 hp is more than enough for any streetcar, Louis has talked about turning up the boost.

Car: 2008 Corvette Z51
Owner: Louis Pepe
Block: LS3, 418cid
Compression ratio: 8.7:1
Heads: LS3, CNC ported, 2.165 intake, 1.59 exhaust valves
Cam: Comp Cams hydraulic roller, 247/247 duration at .050, .624/.624 inch lift, 118 LSA
Rocker arms: Yella Terra, 1.8:1 ratio
Pistons: Wiseco, forged
Rings: Wiseco
Crankshaft: Callies Compstar, forged
Rods: Callies Compstar, forged
Throttle body: Ported stock
Fuel injectors: 120 lb/hr
Fuel pump: Stock in-tank, Fuelab Prodigy 42401 external
Ignition: Stock coil-near-plug, NGK BR7 plugs
Engine management: Stock, tuned by Matthew Pospishil
Power adder: GT-91 turbo
boost: 18psi
intercooler: CX Racing air-to-air
wastegate: JGS 60mm
Exhaust system: Custom 2-inch turbo headers, 2.5-inch crossover, 4-inch downpipe, American Racing Headers Race muffler
Transmission: TR6060
Clutch: SPEC Super Twin
Driveshaft: Stock
Front suspension: Stock lower control arms, shocks, leaf springs, shocks, and sway bar
Rear suspension: Stock lower control arms, shocks, leaf springs, shocks, and sway bar
Rear end: Stock IRS, 3.42 gear, posi
Brakes: Stock
Wheels: CCW 17x4.5 front, 18x12 rear
Front tires: M&H 185/50/17
Rear tires: MT 345/35/18 drag radials
Fuel: E85
HP/TQ: 1,068/1,028


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