The time has come when having a 9- or 10-second street car is obtainable, provided you have the means and the know-how. Fortunately for Tom Deskins of Abingdon, Virginia, he meets both criteria, and with a little help from Lingenfelter Performance, his rare '99 Firehawk became a twin-turbocharged, 7.0-liter monster capable of passing any DOT sniffer in the country.
Tom's quest to turn a mild bolt-on LS1 into the boosted C5R-motivated machine it is today began a little over a year ago. "I wanted to see how far I could go completely DOT-legal and really push the engineering envelope," he says. With that in mind, he commissioned Lingenfelter Performance Engineering (LPE) to install one of its time-tested engine packages along with a twin-turbo kit. LPE has long been considered the institution for C5R motors given its racing credentials, so Tom was confident in the company's ability to build an invincible short-block able to withstand the capabilities of LPE's ported heads and twin-turbo kit.
After prepping the '04 C5R block, LPE installed a Lunati forged rotating assembly with low-compression pistons. The forged internals would provide a boost-friendly 8.0:1 compression and 428 ci of displacement. LPE's LS1-GT7 forced-induction cam was chosen to actuate the stock 1.7:1 rocker arms for a total of 208/230 degrees duration at 0.050 with 0.554/0.546-inch lift and a 121-degree lobe separation angle. The cam reduces valve overlap to make the most of the LPE CNC-ported LS1 heads. With massaged combustion chambers to accommodate the lower compression and larger bore, as well as enlarged intake and exhaust ports, Tom's stock LS1 heads now achieve 300 cfm intake and 230 cfm exhaust flow at 0.550-inch lift, according to LPE's flow bench. Stainless steel 2.02 intake and high-temp Inconel 1.57 exhaust valves can also be credited for the increased flow.
The hot exhaust gases are recycled through Incon manifolds, with 151/48-inch primaries entering a pair of Garrett GT28R turbos with internal wastegates. Intake air is compressed in the hair dryers and hurled into a pair of bar-and-plate, air-to-air intercoolers with 6x12x3.5-inch vertical flow cores. Mounted in either side behind the front bumper, the intercoolers have the benefit of fresh air from the vents next to the foglights before releasing the intake air into an adjoining Y-pipe and then the FAST LSX intake with LPE 90mm throttle body and a stock MAF. Meanwhile, after exhaust leaves the GT28R's turbine, it is expelled through 2.5-inch downpipes into a Borla Y-pipe with the factory GM catalytic converters and a Borla Cat-Back. Tom also maintains all the factory emissions controls including the air pump, the EGR, and all the O2 sensors.
Between the advanced technology that went into the LS1 cylinder heads and the ball bearing turbos, it appears the only real downside to staying completely DOT legal is finding traction. Despite using the super-sticky Mickey Thompson ET Street drag radials, it is nearly impossible to keep the rear tires from spinning. Tom's Firehawk was originally designed and tuned by LPE to run 16 psi of boost. Stocked with 50-pound, high-impedence (factory style) injectors, a Walbro 255-lph fuel pump, and an Incon boost-indexed fuel-pressure regulator, the Navy Blue Metallic Bird seems to be well prepared.