Harken back to the heyday of the musclecar revolution and imagine using hindsight to sit across the desk at your favorite Chevrolet dealer to order up a 1967 Corvette with the legendary RPO code L88. For a scant $947.90, you could have checked the option for the aluminum headed 427 that was conservatively rated at 430 gross hp (at 5,200 rpm) and 460 ft-lbs of torque (at 4,000 rpm). The Chevrolet big-block featured a 4.251-inch bore, 3.76-inch stroke and 12:5:1 compression. With a mechanical lifter camshaft that featured 264 degrees of intake and 269 degrees of exhaust duration (measured at .050-inch lift) with .560-inch intake and .580-inch exhaust lift, it was designed to be revved to 6,400 rpm, where it would wake up and reach its power potential. This was a solid lifter race motor, never meant for daily driving. GM tried to keep the actual horsepower of approximately 500 a secret, and to a degree was successful with only a mere 216 Vettes factory equipped with the L88 from 1967-69.
Fast forward to 2006 and you can walk into your Chevrolet dealer and check off option code 1LZ or 2LZ and order yourself a new Z06 Corvette featuring the 7.0 liter (427 cubic inch) LS7 engine. The upgrade to a Z06 carries with it a $21,200 price tag, but includes much more than the LS7 engine and its crate motor retail price of $13,895 (under PN 17802397). Carrying a conservative net horsepower rating of 505 (at 6,300 rpm) and 470 lb-ft (at 4,800 rpm), the all-aluminum engine is the ultimate factory Gen IV small-block and a direct descendant of the impressive C5R racing efforts. The rigid aluminum block carries 6-bolt main caps, a 4.125-inch bore by 4.00-inch stroke, and an 11:0:1 compression rating. The hydraulic roller cam specs out at 230/231 at .050 with .591-inch lift on 1.8 roller rockers and is designed to be revved up to 7,000 rpm.
LS7 owners looking for increased power are doing exactly what the original L88 owners did; replacing the cam, exhaust manifolds and exhaust system with the best that the aftermarket has to offer. Horsepower of 550-575 was obtainable with the L88, but along with the power came a radical idle and poor street manners. Since the LS7 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? Enter Horsepower Engineering (HPE) of Houston, Texas. Founded in 2001 by owner Chuck Anders, the 13,000 square-foot facility has been pushing the envelope on late model GM performance. As the shop that lays claim to the fastest LT1 F-body, along with the fastest stock block LS1 in the country, big power and HPE go together.
According to Chuck Anders, "the LS7 is a fantastic engine with excellent street manners. Substantial power gains can be achieved by optimizing the camshaft and the exhaust system. Our C6ZS2 (Stage II) camshaft package was custom designed for the owner desiring stock like drivability, moderate lope at idle and noticeable power gains. Although the Z06 features hydro-formed tubular steel exhaust manifolds and a 3-inch exhaust system, the LS7 heads are quite restrictive on the exhaust side. Anything you can do to increase the flow of the exhaust helps power on the LS7." By utilizing a set of the new D-port Kooks 1 7/8-inch headers and 3-inch mid-pipe with high-flow metal substrate cats, increased exhaust duration is allowable due to the excellent scavenging of the Kooks components. Throw in a ported HPE throttle body and a Halltech PowerCore air filter and the engine wakes up very nicely.
Follow along as HPE searches for big power on an LS7 by installing a custom ground camshaft, Kooks headers, Kooks mid-pipe with high-flow cats and a Halltech PowerCore high flow LS7 air cleaner on a 2006 C6 Z06, owned by Sanjay Mehta, a radiation oncologist from Houston, Texas. With a mere 3,500 miles on the odometer, his stock-configured Z06 belted out 465 rear-wheel horsepower. Shop manager and lead technician Josh Ledford of HPE will handle installation of the components while HPE owner Chuck Anders will dive into the powertrain control module and retune the car to maximize the power potential. After wrenching and replacing the parts, we'll show you how much power was added to a bone stock Z06. Will the LS7 respond to the changes much as the L88 did and put out close to 575 horsepower?
HPE's Z Series Camshaft and Power Packages
The HPE C6Z series of camshaft packages retails for $999.95 and consists of cam, dual valvesprings, titanium retainers, Super 7 locks, locators, seals, custom length pushrods, and new crankshaft balancer bolt. The custom-ground COMP Cams are offered in Stage I, II and III varieties. The Stage II cam specs as used in our test car, come out at 230/242 at .050 on a 114 LSA with a .607/.620 lift on 1.8 rockers. The Stage III cam specs are under lock and key somewhere in the Dominican Republic and would require 32 members of the Mafia and one very loud 300-pound opera singer to get them past Chuck's lips.
COMP also supplies the custom length Hi-Tech 3/8-inch pushrods. The pushrods are a one-piece design constructed of 4130 seamless chromoly with an outstanding wall thickness of .080 in. The pushrods are heat treated to a "60" hardness on the Rockwell "C" scale and finished in a black oxide.
Patriot Performance "Gold" dual valvesprings (PN 8401) are capable of up to .650 lift and include titanium re-tainers, machined bases, Super 7 locks and Viton rubber intake and exhaust seals. The Patriot Gold springs feature an open spring pressure of 380 pounds, with 135 pounds closing pressure as compared to approximately 310 and 110 pounds for the factory springs.
In addition to the camshaft packages, HPE offers the following components to make up a Power Package. Key to the power packages is intake and exhaust changes designed to maximize flow.
The Kooks headers ($909.95) are constructed of mandrel bent T-304 stainless steel and feature 1 7/8-inch primaries and heavy-duty 3/8-inch flanges. The D-Port equal length headers feature 3-inch collectors with integral scavenger spikes. All pipes are TIG-welded with the inlets and collectors hand ported to ensure maximum flow.
The Kooks 3-inch mid-pipe ($703.95) features an aluminized center section with a built-in X crossover and two hi-flow MagnaFlow stainless steel catalytic converters. The 3-inch version bolts onto the 3-inch collectors of the Kooks headers and exits at 3 inches, accommodating the Z06 cat-back. The X crossover is positioned as far forward as possible to help scavenge additional exhaust from the engine. An off-road X-pipe is also available. Both systems require the Kooks four-piece O2 sensor extensions to take care of the revised O2 sensor placement on the header and mid-pipe.
HPE's custom throttle body porting service ($125.00) reworks the GM 90mm casting to remove the machined in leading edge to allow 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 typical gains are 7-10 rwhp. All work is done in-house.
The Halltech Z06 High Flow PowerCore air filter (pictured on right) retails for $199.95, and the company claims the filter features 19 percent lower restriction at 850-cfm than the stock Delphi OEM PowerCore filter supplied by the factory.
After completing the exhaust, install the crankshaft balancer and the remaining components that were removed to facilitate the transformation. Fill the engine with eight quarts of factory fill Mobil 1 and replace the Dexcool with fresh coolant. After checking the car over several times, Josh fires up the willing LS7 and allows it to idle, while carefully checking for any fluid or exhaust leaks. Once verified, the car is allowed to cool before being strapped onto the dyno where Chuck Anders refines the idle, air-fuel and timing tables until the LS7 is ready to be unleashed.
Recommended Parts and Supplies:
LS series valve tool
Wire wheel or wire brush
When the HPE Z06 camshaft and power packages were installed and the final tuning tweaks were made, the LS7 responded to this mild camshaft upgrade by picking up a total of 48 hp and 44 lb-ft of torque at the wheels. The addition of the Halltech high flow air cleaner boosted the gains up to 51 and 46 hp and torque, respectfully. Just as important as the peak numbers are the phenomenal increases across the entire power band. It's one thing to desire a radical idle and stratospheric peak numbers, but this engine makes gobs of power without sacrificing anything in the way of drivability. The idle has just the slightest hint of a lope and until the driver cracks open the throttle to allow the dual-mode muffler to vent exhaust without baffling, nobody would be the wiser that over 500 rear-wheel horsepower lurks in the car.
According to Z06 owner, Sanjay Mehta, "In stock form, the Z06 was a screamer from the day I drove it off the Bowling Green assembly line, but didn't quite have the power of my LPE 415 ZR1 or Procharged C5. Although the camshaft package was small, it fit my needs. The car runs beautifully, and these mild mods really bring out the personality of the LS7. It will now run neck-and-neck with my LPE 415 ZR-1, and it feels quicker below 4,000 rpm on the street than the Procharged C5. The effortless power at any RPM is intoxicating ... it really roars above 4,000, but I can pass smoothly at 1,800 rpm in Sixth. The cam has a very mild lope ... enough to know something is going on, but not enough to be annoying in traffic. I wanted to retain the stock drivability and reliability, while unleashing some of the potential of the LS7. During before-and-after quarter-mile drag testing at Houston Raceway Park, the best stock run was an 11.8 at 123.5mph on a 2.1 60-ft time with the stock Goodyear F1 tires. After the power package installation, the Z06 turned an 11.35 at 130 mph with a 2.05 60-ft time. Of course, I was promptly booted off the track for running below 11.50 without a roll bar, so I switched on the A/C and XM radio for the cruise home. No detonation, no clutch issues, no Check Engine lights, just stock like drivability, with more power and a crisper, more authoritative sound." According to Chuck Anders, owner of HPE, "I was happy to see that the Z06 responded as well as it did to the mild camshaft and exhaust changes. The extremely refined nature of the LS7's heads and the excellent factory exhaust make it more difficult to achieve the type of results we see on LS1 and LS2 engines. Even with the mild Stage II cam, the engine is putting out right at 575 horsepower at the crankshaft. Not bad for a motor that will pass any emissions test in the country and propel a Z06 to very low 11-second time slips. Additional power gains can be coaxed out of the LS7. We have several customers who have put down over 550 rear-wheel horsepower by going with our Stage III Power Package, even a couple have made over 560, with the only changes being the use of the off-road Kooks mid-pipe and an electric water pump. Mild or wild with an LS7 and the results are the same--phenomenal street power!"
Testing of the 2006 C6 Z06 Corvette was performed at Horsepower Engineering in Houston, Texas. HPE has both Dynojet Model 248 and Mustang MD-1750 in-ground dynos. 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 Z06 required both part and full throttle dyno runs to dial-in the computer program using LS7 Edit.
All testing was done in Fourth gear with traction control off. The barometric pressure, air intake temperature and SAE correction factors for the run are listed here. Correction factors use a standardized SAE calculation, which include reference temperatures of 77° Fahrenheit, and a barometric pressure of 29.23 inches of mercury.
Test Number 1 - Stock Z06, Test parameters: Inlet Air temperature 64.1° Fahrenheit, barometric pressure 30.14, Humidity 6%, correction factor .95
Test Number 2 - Z06 with Camshaft, Power Pack and Tuning, Test parameters: Inlet Air temperature 89.5° Fahrenheit, barometric pressure 30.08, Humidity 26%, correction factor .99
Test Number 3 - Z06 with Camshaft, Power Pack, tuning and Halltech air filter, Test parameters: Inlet Air temperature 90.3° Fahrenheit, barometric pressure 30.11, Humidity 24%, correction factor .99