Equipped with a 400-horse, all-aluminum, 364ci LS2 powerplant, an '05 or '06 GTO is a sophisticated modern-day musclecar. Dubbed a "Gen IV small-block" by GM, the LS2 took the LS1's bore of 3.90 inches and brought it out to 4.00 inches while retaining the same 3.62-inch stroke. Compression was raised from 10:1 to 10.9:1 by the use of flat-top pistons and the more efficient LS6 cylinder heads that debuted on the Z06 Corvette. Conservative camshaft specifications of 204/211 at 0.50 and 0.520/0.520 lift on 1.7:1 roller rockers and the 116-degree lobe-separation angle ensure a smooth idle and crisp performance. With 400 lb-ft of torque on tap, stock GTOs routinely rip off low-13-second e.t.'s while simultaneously providing one of the most balanced ride-and-handling packages ever offered by a domestic manufacturer. So why mess with success? Because there is no such thing as too much horsepower.
LS2 owners looking for more are doing exactly what many original GTO owners did: replace the cam and exhaust system with the best the aftermarket has to offer. Although 500 hp was obtainable with a built 389, along with the power came a radical idle and poor street manners. Since the LS2 idles as well as any modern car of its generation, what would happen if you swapped out the cam for a more aggressive design and freed up the exhaust? How much more power could be added by putting on an LS2-specific nitrous-oxide system?
Enter Horsepower Engineering (HPE) of Houston, Texas. Founded in 2003 by owner Chuck Anders and currently housed in a 13,000-square-foot facility, HPE has been pushing the envelope on late-model GM performance ever since.
According to Chuck Anders, "Substantial power gains can be achieved with the LS2 by optimizing the camshaft and the exhaust system. Our GTO Package has at its heart either a 'C' or 'S' series camshaft. The 'C' series cam was custom-designed for the owner desiring stock-like driveability, moderate lope at idle, and noticeable power gains. Owners looking to maximize the power of their LS2 with an aggressive cam choose our 'S' series cam.
"Although the LS2 exhaust manifolds are an improvement over the LS1 design, a highly efficient exhaust system that utilizes either American Racing's or Kooks 171/48-inch stainless headers and 3-inch connection pipes will really allow the heads to flow to their capabilities. Combine the camshaft package and enhanced exhaust flow with custom PCM tuning, a Lingenfelter cold-air kit, a ported throttle body, and an underdrive pulley, and we routinely get gains of 80-100 rwhp.
"Owners looking to make over 500 rwhp can opt for the Nitrous Package, which features a Cold Fusion Nitrous plate system that is jetted to safely add another 100 hp. Optional equipment, such as the Cold Fusion billet-aluminum remote bottle opener and bottle heater, adds great functionality to the system."
Follow along as HPE searches for big power in an LS2 by installing a GTO and nitrous package on an '06 GTO owned by Corey Poiencot of Houma, Louisiana. In stock configuration the Goat belted out 344 rwhp at 5,800 rpm. Let's see what it does after the mods. Technician Dan Taber of HPE will handle installation of the components, while HPE tuner Chuck Anders will dive into the powertrain control module and retune the Pontiac to maximize the power potential.
GTO Power Package
HPE's GTO package retails for $2,499 and consists of matched cam and exhaust components and a few other items.
Each customer has a choice between either a "C" or "S" series camshaft custom-ground by Comp Cams. The "S" series cam used in the test car features an aggressive duration of 238/240 degrees at 0.050 on a 112-degree LSA and 0.605/0.609 lift with 1.7 rockers. Conversely, the "C" series camshaft, though it's also a strong performer, specs out at a more mild 232/234-degrees duration at 0.050 on a 112 LSA and has 0.595/0.598 lift with 1.7 rockers.
Patriot Gold dual valvesprings, titanium retainers, Super 7 locks, locators, Viton rubber intake and exhaust valve seals, and Trick Flow 7.40-inch-length, 51/416-inch one-piece chrome-moly pushrods complement the cam.
American Racing Headers (ARH) or Kooks Custom long-tube headers with 171/48-inch primaries are also utilized. Each header is fully mandrel-bent T304 stainless steel with heavy-duty 31/48-inch flanges and 3-inch collectors for excellent flow. A 3-inch off-road connection pipe from ARH or Kooks is included as well. Each header kit has O2-sensor extensions to take care of the revised O2-sensor placement on the header and connection pipe.
The Lingenfelter Performance Engineering (LPE) GTO Performance air intake for the '05-'06 GTO consists of an air-filter assembly and filter housing that includes an S&B cotton-gauze, washable air filter. It replaces the factory airbox with a custom-manufactured airbox that was designed to form-fit into the old airbox location. Rubber seals on the bottom and top of the box seal out transient heat from the engine, allowing the intake to pull cool, dense air from behind the grille and core support.
An Auto Specialties Performance (ASP) harmonic-balancer underdrive pulley replaces the factory harmonic-balancer pulley and slows down the accessory drive by 25 percent, reducing parasitic drag. The ASP pulley is constructed of aluminum and is SFI rated.
NGK TR-6 V-Power spark plugs feature a patented V-groove center electrode that forces the spark to the outer edge of the ground electrode, placing it closer to the air/fuel mixture.
MSD 8.5mm Super-Conductor spark-plug wires are available in red or black and feature dual-crimp terminals and factory-style plug boots. The 8.5mm jacket is constructed of silicone and proprietary synthetic materials to protect against high heat and abrasion.
GTO Power Package Options
• HPE's Custom Throttle Body Porting Service ($150) reworks the GM 90mm casting to remove the machined-in leading edge, allowing for a smoother transition of air into and out of the throttle body. The porting service is available for all LS-series throttle bodies, and all work is done in-house.
• Hypertech's 160-degree PowerStat (PN LS2-160, Retail $35.18) thermostat combined with custom programming of the GTO's fans improves performance by allowing the engine to run cooler, thereby reducing the chances of detonation under load, which can damage components.
• HPE's Custom Dyno Tuning ($425) ensures maximum safe horsepower. The company uses LS2edit for '05-'06 GTOs, as well as a Dynojet Model 248 dyno and a Mustang MD-1750 in-ground dyno for tuning purposes.
• GTO Package Installation (PN, LBR, Retail $1,100). Professional installation of the GTO Package is highly recommended and should be completed by a mechanic who has the knowledge and specialty tools necessary to perform major LS-series engine work, such as camshaft and valvespring replacements. Labor generally takes 12-14 hours depending on the level of options chosen.
GTO Nitrous Package
HPE's GTO Nitrous package retails for $650 and fits the '05 and '06 GTO. It features a kit made by Cold Fusion Nitrous of Houston, and it contains a wet-plate system designed for the LS2. Cold Fusion was founded by Mike Wear in 1995 as a nitrous manufacturing company that supplied solenoids and all manner of nitrous parts to many of the large retail-based companies. After 5 years, Cold Fusion began selling retail, manufacturing all of its products in the United States.
The Cold Fusion Nitrous LS2 Plate kit features a 90mm, billet 6061-aluminum plate that mounts to the LS2 throttle body, N2O and fuel Super Power solenoids, a 10-pound bottle with a high-flow valve and liquid-filled pressure gauge, and all necessary accessories such as braided stainless steel lines, wiring, and a throttle-activated window switch.
Nitrous Package Options
Although the GTO Nitrous Package lists as a kit, the following options are commonly added by customers when ordering a nitrous system. On the subject '06 GTO, each of these options was chosen except the bottle-heater pressure switch.
• Cold Fusion Remote Bottle Opener (PN CFN-117C, Retail $199.95). Since the valves on nitrous bottles should not be left open, invariably an owner has to pull over to the side of the road, pop the trunk, and open the nitrous valve. The Cold Fusion remote bottle opener allows the owner to open and close the nitrous bottle from the driver seat. Made of billet aluminum and featuring an advanced servo-powered motor, the bottle opener fits all standard-size nitrous bottles including 5, 10, 15, and 20-pound units. Integral to the design is a quick-release mechanism that allows the valve to be removed for bottle filling. Included in the bottle opener are plug-and-play connectors and a switch.
• Cold Fusion Purge Kit (PN CFN-1700, Retail $89.95). For consistency and the most power, any nitrous vapor in the lines should be removed, allowing the liquid N2O to be available to the nitrous solenoid for instant power. The Cold Fusion 4AN purge kit comes with an electric solenoid, a 4AN adapter fitting, a 11/48-inch hex nipple, and both fittings for the inlet and outlet with 28-inch 11/44 poly line.
• Cold Fusion Bottle Heater (PN CFN-104, Retail $84.00) and Bottle Heater Pressure switch (CFN-103, Retail $48.95). The company recommends running a bottle pressure of between 950 and 1,000 psi in order to ensure the gaseous content of the nitrous has turned into a liquid. In general, temperatures of between 85 and 95 degrees Fahrenheit will provide the proper pressure. Bottle pressures below the optimum range don't provide enough nitrous and the car will tend to run rich, while excessive pressures can cause a lean condition. Cold Fusion offers a 12-volt, 300-amp bottle heater that wraps around any standard-size bottle and is secured with Velcro straps. When combined with a bottle-heater pressure switch, the owner can open the nitrous valve, turn on the heater, and allow the adjustable switch to regulate the pressure.
The Super Power solenoids were mounted on the fenderwell. Each one has 0.130-inch inlets and outlets and employs a Teflon plunger and Viton seals.
• MSD Electronics Digital RPM Window Switch (PN 8969, Retail $99.99). An MSD programmable rpm window switch is used to determine when the nitrous system is turned on and off. Once the switch receives a wide-open throttle signal, it will activate only when it is between the predetermined rpm window. The subject GTO is programmed to come on at 3,200 rpm and to stop at 6,400 rpm. This switch is wired into the GTO's ECU and in essence reads rpm out of the computer to enable it to send a signal to the nitrous solenoids to open or close. The MSD switch works in conjunction with the standard Cold Fusion wide-open-throttle window switch, which is mounted under the gas pedal inside the vehicle.
• Nitrous System Installation (PN, LBR, Retail $500). Professional installation of the Cold Fusion Nitrous kit is highly recommended. In addition to the obvious challenges of mounting the solenoids and bottle brackets, a good knowledge of automotive electrical systems is required to get the systems to operate properly. Installation of accessories such as the remote bottle opener, bottle heater, RPM window switch, and purge kit are priced at $100 for each. In total, because the package and accessories were installed together, the total labor was reduced to $750. Labor to install the nitrous system, along with a complementary retune of the computer to ensure safe engine operation, took a total of 10 hours.
Conclusion
When the HPE GTO Power and Nitrous package installations were complete and the final tuning adjustments were made to the ECU, the LS2 responded by picking up a total of 176 hp and a phenomenal 199 lb-ft of torque at the wheels. The GTO Package showed outstanding gains of 91 hp and 55 lb-ft of torque at the wheels, and the large-duration cam doesn't seem to have negatively impacted the low-end torque. On the contrary, torque gains between 3,000 and 6,000 rpm are consistent, showing that a properly designed and matched camshaft package can increase horsepower and torque across the full spectrum of the rpm range versus trading top-end power for low-end torque, which has been the case for decades in many old-school engines.
Cold Fusion's nitrous bottle is installed in the trunk and is outfitted with the optional remote opener and heater. The former allows the driver to open the bottle from the cockpit, and the latter helps ensure consistent bottle pressure.
Adding the 100-shot of the Cold Fusion Nitrous kit boosted rear-wheel horsepower by 99, but more importantly, put up staggering torque gains of 155 lb-ft. Not only were the torque gains huge, the peak numbers came in a full 600 rpm below the peaks on the Power Package.
According to Chuck Anders, HPE owner, "Both the 'S' and 'C' cam GTO Power packages work extremely well either with or without a power adder such as nitrous. Although the peak numbers of the 'C' package average 10-15 rwhp lower than the 'S,' the broader torque curve is perfectly suited for the daily driver. In designing cams, the LSA and overlap played key roles in balancing peak power and average torque. By using extremely aggressive ramp rates, the LSA could be tightened, yet we could still retain good idle quality and torque. Both cams have additional exhaust duration to take advantage of the off-road header and connection-pipe exhaust system.
"When you add in the Cold Fusion Nitrous kit, the atomization provided by the innovative 90mm plate system really helps fill the cylinders, especially in the meat of the torque curve, and provides excellent power gains. From a convenience perspective, enthusiasts love to be able to remotely monitor and arm their nitrous systems."
Cold Fusion's Purge Kit was also added to this system to clear the lines of nitrous vapor, thereby ensuring liquid nitrous is at the ready the instant the nitrous comes on photo courtesy of manufacturer.
According to Corey Poiencot, a 24-year-old machinist and owner of the subject GTO, "In stock form the LS2-based GTO was powerful but, due to the refined nature of the platform, never really felt fast enough. All of that changed in an instant when I drove the car to HPE in Houston for installation of the GTO Package.
"Though the GTO is a daily driver, the aggressive 'S' cam idles well and pulls hard to the redline of 7,000 rpm. Adding almost 100 rwhp to the engine by swapping in a cam and related exhaust and intake components really woke up the car and gave it an aggressive personality. I was so impressed by the quality and performance of the work that I scheduled a second trip into Houston to have the nitrous package installed. I really like how the Cold Fusion kit mounts with a plate directly behind the throttle body, along with all of the accessories that will allow for increased convenience and performance.
"When the nitrous system engages at 3,200 rpm, the Goat pins you back in the seat and takes you for a wild ride. Although my stock LS2 clutch probably won't last long, I plan to upgrade the clutch and get the car out to the local quarter-mile dragstrip to see if I can turn some low-11-second e.t.'s."
GTO Package
Testing of the '06 GTO was performed at Horsepower Engineering in Houston, Texas. HPE has both a Dynojet Model 248 and a Mustang MD-1750 in-ground dyno. An in-car monitor is used to collect real-time air/fuel ratio (A/F) data on the load-simulating Mustang Dyno, while the Dynojet is used for final dyno results. The GTO required both part- and full-throttle dyno runs to dial in the computer program using LS2edit.
Configuration AIT HP RPM Torque RPM + HP/TQ Stock 58.6 343.8 5,800 350.0 4,500 - - - - GTO Package & Tuning 77.5 434.3 6,{{{300}}} {{{405}}}.0 4,800 {{{90}}}.5/55.0
Nitrous Package + GTO Package
After the Nitrous package was installed, the car was tuned again to ensure safe operation. Timing was unaltered until 4,000 rpm where 1 degree was pulled out; then at 4,200 through the redline of 7,000 rpm, 2 degrees were removed. These changes, along with a slightly revised air/fuel ratio of 12:1 (versus 12:5:1) in the same 4,200-7,000 rpm powerband resulted in a drop in naturally aspirated peak rear-wheel horsepower from 434.3 to 421.0. Torque was also down from 403.2 to 393.5. The GM LS2 ECU is not capable of storing two separate tunes, so the final tune was optimized for nitrous use.
Configuration AIT HP RPM Torque RPM + HP/TQ GTO Package with Nitrous Tune 69.0 421.0 6,300 393.5 4,800 - - - - GTO Package with Nitrous Package& Nitrous Tuning 69.0 519.9 6,300 548.7 4,200 98.9/155.2 Grand Total - - - 519.9 548.7 - - - - 176.1/198.7
