While the new Z06, with its 505hp LS7 engine, may be a relative bargain-that is, if you're also shopping cars with the label "Built in Maranello"-it doesn't automatically fit the budget of every Corvette-performance junkie. Indeed, with a base price of $65,690, the '06 Z06 commands an approximately $21,000 premium over the standard, LS2-powered Vette.
The gulf in sticker prices may be wide, but closing the gap in performance isn't as daunting. Pick up any Corvette parts-and-accessories catalog and you'll find a seemingly endless list of bolt-on products designed to boost power. But bolt-ons will make only modest changes, at best. To really affect the output of an engine, you've got to fundamentally change its capacity to ingest and digest air. And since cylinder heads are basically the lungs of an engine, they are generally the most effective way to elicit a dramatic increase in horsepower.
But just as an engine is analogous to a human heart, simply bolting on new cylinder heads doesn't necessarily provide better performance-just as buying a set of new running shoes won't automatically lower your blood pressure. Freer-breathing heads are only effective when complemented with a systematic approach to the engine's breathing-including a camshaft with sufficient lift and duration specifications, which will open long enough to allow the combustion chambers to draw in the greater quantity of air the heads can flow.
The entry and exit points of the engine's breathing must also be expressed, because the heads' flow capability is only as good as the amount of air they can draw from the intake manifold. Similarly, the extra air drawn into the engine produces a greater quantity of exhaust gases, so an upgraded exhaust is warranted, too.
When it comes to figuring out the best combination of aftermarket heads, intake, camshaft, and exhaust, you could either go back to school and earn that engineering degree or turn to someone who has already figured it all out. The latter choice was the path Tampa resident Robin Wahler chose when seeking to increase the horsepower of his red, automatic-equipped C6. He took the car to Tampa's Rev Xtreme tuning shop for a holistic approach to increasing the output of his Vette's heart.
Rev Xtreme has put together a head-and-cam package for LS2 owners seeking Z06-like performance. The basic recipe includes a set of ET Performance 215 cylinder heads with 58cc combustion chambers, a Comp Cams camshaft with 0.581/0.588 lift andand other bolt-ons. 224/228 duration, a modified FAST intake manifold, LG Motorsports long-tube headers,
"It's a great combination of parts because there are no compromises in engineering, performance, or driveability," said Rev Xtreme's Dino Clark. "For someone who's looking for a car that operates and drives mostly like a stock Corvette, but with a ton more power, it's the way to go."
With the new parts and requisite tuning, output on the red Vette jumped from its baseline of 311 rear-wheel horsepower (rwhp) to 443 rwhp-an increase of about 43 percent. Depending on the drivetrain-parasitic-loss factor you use, which is generally more through an automatic transmission, the increase in horsepower puts flywheel output on par with the Z06. That's none too shabby for about $5,000 in parts, installation, and tuning charges.
The way we figure it, Wahler's Vette has attained Z06 performance for a quarter of the cost difference between it and the standard C6's base price. This is daily drivable, normally aspirated horsepower that doesn't have an adverse effect on driveability or comfort. And with its stock appearance, this little red Corvette is sure to surprise more than a few stoplight warriors.
Rev Xtreme's package is built around ET Performance's 215 LS1 cylinder heads. The 215 designation refers to the 215cc intake ports. The LS2's stock heads have 210cc intake ports-remember, they're from the previous LS6 engine, not the LS1, which had 200cc ports. ET Performance CNC-ports the heads, carving out the larger flow path the company says flows 301 cfm at 0.500 inch of valve lift. Exhaust flow at 0.500 is 204 cfm, giving the heads a healthy exhaust-to-intake flow ratio of 69 percent.
The heads are all-new castings with thicker-than-stock decks and valve angles rolled back to 11 degrees. Also, the valves are moved closer to the center of the cylinder bore to unshroud them. And while 5 cc doesn't seem like a large increase, it's enough to increase flow by approximately 14 percent over stock. That's a 14-percent flow increase in all eight cylinders-a significant gain for an engine with unchanged displacement.
The heads on Wahler's engine also boast 58cc combustion chambers, which are 6.5 cc smaller than the stock LS2's 64.55cc chambers. This effectively gives the engine slightly higher compression, but with careful tuning and a strict adherence to premium fuel, detonation isn't a problem. The heads also have the stock-size 2.00/1.55-inch valves. The heads retail for about $2,400; a pretty good value, if you ask us.
Camshaft and Valvetrain
Selection of the camshaft fell to an aggressive Comp Cams grind, the Xtreme XE-R, with 0.581/0.588-inch lift specs, 224/228 duration specs, and a 114-degree lobe separation. Comp's XE-R grinds are designed primarily for normally aspirated applications, like Wahler's LS2, giving the valves plenty of hang time to ingest air and expel exhaust gases. The Xtreme XE-R cam works particularly well at high rpm, where the LS2 belts out tremendous power with its increased airflow.
The new cam's specs are abstract, however, without comparing them with stock specs. The '02-'04 Z06 factory camshaft, on which the LS2's cam is based, was good for 0.550/0.550-inch lift and 204/218 degrees of duration at 0.050-inch lift. The lobe-separation angle was 117.5 degrees.
With its more aggressive nature, the Comp camshaft gives the LS2 an unmistakable "rump" at idle, sort of reminiscent of an old-school, hear-every-piston-fire big-block. Frankly, it sounds great, but tuning to maintain a good idle quality can be tricky.
The higher-lift characteristics of the camshaft negate the use of stock valvetrain components, including the rocker arms and springs. Stiffer double-style springs and 1.7-ratio roller rocker arms, all from Comp, were installed.
Intake and Exhaust
This modified LS2 draws its breath through a Halltech Stinger cold-air intake system, sending the air to a modified FAST LSX intake manifold, modified by A&A Corvette Performance to fit better beneath the C6 hood. The Halltech intake keeps the mass-air sensor in roughly the stock location, so air metering and tuning issues are negligible to nonexistent.
While comparisons with a FAST intake and a factory intake may show little difference on a stock engine, the airflow advantage is clearly evident on a modified engine such as this one. The FAST intake, like the new camshaft, really shines at higher rpm, providing not only an increased volume of air, compared with the stock intake, but excellent velocity.
While the intake system supports the airflow into the engine, a set of LG Motorsports Pro long-tube headers backs up the engine's exhaust-expelling requirements. These are monster, stainless steel headers, with 1.75-inch primary tubes that stretch 32 inches in length. And while not CARB-certified, they may be configured, as Wahler's car is, with high-flow cats mounted to a 3-inch X-pipe.
Along with the heads, cam, and intake/exhaust mods, Wahler's Corvette also received an ASP underdrive pulley, a 160-degree thermostat, and a pair of Corsa's free-flowing, great-sounding Sport mufflers. The whole package was installed at Rev Xtreme, with tuning performed by Jeremy Formato.
"Every car is different, but our experience with these head-and-cam packages means we can usually get the tuning done in two or three hours," said Clark. "Idle quality on Robin's car is great; it's his daily driver, so a good idle was a must."
The engine's 311-rwhp baseline performance was typical for an automatic C6, but Clark says the car's final 443-rwhp output was actually a bit lower than it might have been under different circumstances. "We installed a looser converter, with a stall speed of about 3,200-3,600 rpm," he said. "That always masks horsepower on the dyno. The car is probably putting out about 460 hp through the tires on the street."
That's considerably more than the street output of the vaunted Z06. For those whose checkbook balance won't quite stretch to nearly $66,000, Rev Xtreme's simple, but effective, heads-and-cam combo proves there are more economical ways to have the fastest Vette on the block.