With the refined nature of today's high-performance GMs, it's easy to forget the endless man-hours needed to make them that way. But that distant memory comes charging back when we bolt up a part that perhaps wasn't the best for streetability, in the quest for more power. It's at that time, when the SES light is burning, the untuned EFI mill is pig-rich, and that aftermarket tuning software that we told ourselves we'd learn how to use is staring us in the face, that we truly start to appreciate the effort needed to create the complete performance package.
As far as performance packages go, they don't get much more complete than the Corvette C6. Jumping off from the damn-good-already C5, a 400-horse LS2 (with a very underrated 400 ft-lbs of torque) and a host of other refinements move the '05-up Vettes ever closer to the blue-blooded world of Porsches and Beemers. That the C6 retains the bang for the buck world title is a given.
Yet there are those who feel that the C6 is too refined. Aurally, the stock exhaust is seriously toned down; when combined with the cabin's outstanding soundproofing, it takes some rpm before the LS2 makes its presence known. The dreaded torque management is back, eager to extend your tranny's lifespan while sucking away power. And let's not forget the Extended Mobility "runflat" tires-a great idea ... for a Malibu. Yep, there's no doubt that this car can be improved upon-but can it be done without losing its pedigree?
One company that attempted this tall order is SLP. Its ZL465 package is not a complete overhaul-more like a carefully chosen group of bolt-ons, a tailored tune, and some optional appearance upgrades that retail for $4,474.
We got wind of SLP's plans when Director of Engineering Brian Reese mentioned that the Toms River, New Jersey-based company was creating a PerformancePac for the new C6. At the time, the LS2-based Vette was brand new, as was its hack-resistant, CAN-based ECM. Scoring a spot on a bad FOX reality show is much easier than cracking this sucker, so we figured that it would be awhile before SLP came up with a pilot ZL465. Mere months later, Reese called us up and asked, "Where do you want it delivered?" Englishtown, my good man!
Here's the ZL465 skinny: as you've probably guessed by now, this designation refers to the amount of flywheel horsepower afforded by the mods. They include a full exhaust upgrade with SLP's 1.75-inch, 4-into-1 coated long-tube headers, 3-inch, high-flow cats, a stainless crossover pipe, and a PowerFlo(tm) cast tip exhaust system. On the intake side, there's an SLP/Blackwing(tm) induction package and an in-house set of 1.85-ratio rocker arms.
A 160-degree thermostat replaces the 195-degree stocker, and SLP will provide custom dyno-based tuning. I say "will", because the ZL465 that we tested didn't have a cracked ECM; only an external "timing tricker" worth maybe 2 degrees of advance. Other, non-performance changes include ZL465 exterior badging and a host of optional interior dress-ups.
On top of those goodies, the automatic-equipped pilot car that showed up at E-town had the following extra mods: SLP 25 percent underdrive SFI balancer, 3.90 rear gears, ACS/SLP lip spoiler, 1/2-inch suspension lowering, and Michelin Pilot PS2 tires. While not part of this PerformancePac, SLP sells everything except for the 3.90 gears and tires.
Since both power and suspension settings had been altered in the ZL465, we ran it on the famous Raceway Park quarter-mile, then set up a few cones on our Real-World Skidpad for some g-testing. Here's what we found:
Overall drivability is very close to a stock C6. The ZL465 starts, idles, goes off-idle, and transitions no differently, and it's crisper thanks to the intake and exhaust mods.
The 3.90 gears and gummy meats enable the type of head-snaps unseen in a factory car. Michelin's PS2s are probably the stickiest true street radials that we've ever driven-idling after a nice smoky burnout, I could damn-near flat-foot it and this puppy would hook. The ZL pulled 1.90 to 1.80 60-foots all day long.
The LS2-like any in the great line of GM small-blocks-is easily modified with a few choice components. But every year, those brainiacs in engineering get the latest and greatest engine closer to optimum from the factory, while making the computers more and more complex. Simply put, the aftermarket has to work much harder for a few extra ponies, and cracking the '05-06 codes continues to be a big problem. However, whatever hardships the ZL465 builders went through, none of them were transported into our test car. Without upping the rev limiter to take advantage of the Gen IV's outstanding airflow characteristics, or changing the tune, SLP was able to enhance that awesome C6 power by a few dozen ponies.
There is a real urgency to its acceleration, untamed all the way to the stock 6600 limit. There is slightly more intake noise, but the best sounds come from the exhaust system-finally, some bark to go with the bite! The ZL465 put down repeatable horsepower all day: all six runs were between 118.2x and 118.9x miles an hour. And through slight adjustments to launch technique, I was able to coax the ET down from an initial 12.04, to 11.87 and 11.84, and finally to the best time of the day, 11.79.
While generally abusing this sucker around the cones, the Vette stuck our heads to the side glass like the C5 Z06 did-no small feat when the test surface has an appetite for rubber. The razor-sharp Real-World 'Pad may have taken a chunk out of a PS2's hide-1 inch by 2 inches, to be exact-but that didn't stop the C6 from posting 1.01 clockwise and 1.02 counter-clockwise readings. If you need more grip on the street than this, you're a danger to society and yourself.
It's fair to say that the ZL465 is as much of a complete performance package that we've tested, and definitely good for 4 or 5 tenths over stock. Taking into account the C6's $45,000 base price, that's a good return for your money.