C6 Corvette 500HP Upgrade Kit - Quick Test: SLP ZL500 PerformancePac

Travel with us to the magical land of Toms River, New Jersey, and watch as the performance prestidigitators of SLP Performance Parts summon Z06-level horsepower from this innocuous-looking C6.

Call us automotive fashionistas, but there's something tremendously satisfying about affixing the latest, hippest cloisonn emblem to the fender of one's Corvette-particularly when the badge in question signifies an accompanying increase in horsepower. That being the case, it came as no surprise when Toms River, New Jersey-based performance-tuner SLP Performance Parts recently announced the availability of a new 500hp C6 upgrade package called, appropriately, the ZL500 PerformancePac.

Because we did not litter the SLP dyno shop with Fiery Hot Cheetos during our last visit (see "Quick Test: SLP 330HP PerformancePac," Feb., '06), Team VETTE was invited back for an exclusive first look at the new package. As before, we were impressed with the engineering effort the company put into the kit, which includes a specially picked head/intake combo, an underdrive crank pulley, a host of induction and exhaust upgrades, and package-specific computer programming to tie it all together.

According to SLP Director of Engineering Hank Daniecki, "The goal of the project was to put together a package that could be used on a daily driver with no change to the vehicle's street manners-except for the neck-breaking power. We accomplished the 500hp level by utilizing the stock camshaft, making the ZL500 Pac a true bolt-on package."

Here's a look at what's included in the SLP L92 cylinder head/manifold kit. The heads come complete with Comp 918 springs, titanium retainers, and GM Performance Parts L92 head gaskets. They're decked to a 64cc combustion chamber, but retain the stock 2.16/1.60 valves. Meanwhile, the intake is shipped with a set of pre-installed 40-lb LS7 fuel injectors. This top-end combo accounts for a bigger power jump than any of the other included parts: 32.8 hp and 31.3 lb-ft of torque at the rear wheels.

As with its other Corvette PerformancePacs, SLP developed and tested all of the included components together in an effort to optimize output and eliminate guesswork. The idea behind this "package" approach is to ensure consistent power numbers and eliminate the possibility of parts mismatches.

According to Daniecki, "The highlights are a modified version of GM's L92 cylinder head/intake manifold package and SLP's underdrive crankshaft pulley. We chose these cylinder heads after months of testing on both the engine and chassis dynos. The heads were up-fitted to heavily modified SLP ZL402 [402ci] short blocks, as well as stock LS2 engine assemblies. All tests showed remarkable results using the out-of-the-box head from GM Performance Parts.

"We then decided to mill the L92 cylinder heads to 64cc combustion chambers to match the compression ratio of a stock LS2. This testing resulted in even more power. Testing on both LS2 and ZL402 engines showed results that were even with, or better than, some highly rated-but pricier-aftermarket LS heads. With these results, it was an easy decision to use the new SLP-modified L92 heads in the ZL500 package."

With an '07 Atomic Orange convertible as our test subject, we were afforded a part-by-part look at the ZL500 package, and we were later given a front-row seat as the car was strapped to SLP's chassis dynamometer to lay down the numbers. Before we see how things played out on the dyno, let's take a closer look at the hardware itself.

Labor Times For Installation of SLP ZL500 Performance Pac

This composite photo shows the difference between the stock L92 heads and the finished-chamber SLP version. Note that the SLP heads have their own application-specific casting numbers.

The ZL500 package comes with a choice of four different SLP exhaust systems, all of which run from the midpipe back and are built entirely from stainless steel. Shown above is the PowerFlo system equipped with the company's signature cast tips (Part No. 31076). SLP reps say the PowerFlo exhaust is great if you want to let everyone know you're coming without sacrificing civility under normal driving conditions.

The second exhaust choice is the PowerFlo system with 3.5-inch polished round tips (Part No. 31079, above). SLP says this system is perfect if you enjoy a quiet cabin with the majority of the sound coming from the back of the vehicle. Expect 10.3 hp and 9.7 lb-ft from either of the two PowerFlo systems.