When introduced for the '05 model year, the C6 received the evolutionary Gen IV LS2 powerplant, which carried ratings of 400 horsepower and 400 lb-ft of torque. While the new engine's cylinder heads and cam specs were all but identical to those of the outgoing LS6, the LS2 differed significantly from its predecessors in other areas. Gone were the LS6 intake manifold and 78mm throttle body, replaced by a new-style intake and a 90mm electronically controlled throttle body.
Enthusiasts and the aftermarket naturally deduced that there was potential in the new intake setup, and testing quickly ensued to determine if retrofitting the updated manifold and throttle body onto Gen III platforms could provide an easy and inexpensive performance boost. But surprisingly, it was determined that the LS2 parts didn't perform as well as their old LS6 equivalents, and C6 owners were left to wonder how much power they were leaving on the table by retaining the factory intake configuration.
"According to GM, the LS2 manifold has a marginal increase in plenum volume over the LS6 and [has] similar runner shapes optimized for the 6.0L engine," says Pete Incaudo of VMax Motorsports. "What changed was the technology employed to produce the manifold. The LS1 and LS6 manifolds were produced using a 'lost core' plastic-molding process that produced a single-piece manifold."
The LS1/LS6 intakes used a...
The LS1/LS6 intakes used a "lost core" manufacturing process, which produces a one-piece manifold. Note that this manifold has a 75mm throttle body opening and is distinguishable as an F-car version thanks to its traditional throttle-cable bracket. Although LS1 and LS6 manifolds look very similar, the EGR-tube provisions reveal this one to be a pre-'01 LS1 unit.
The lost-core process involves the use of a low-melting-temperature metal core, which is loaded into a plastic-molding tool, over-molded, and then melted out after the part is formed. Nylon 66 was the material used to produce the LS1 and LS6 manifolds. "The LS2 and LS7 manifolds utilize a more traditional plastic-injected-molding process that produces three different intake-manifold sections, which are then fitted together and vibration welded around the edges," says Incaudo.
Vibration welding, sometimes referred to as "sonic welding," involves melting the composite together after vibrating the materials to produce enough friction for a weld. Although the new manifold material looks similar to that used in an LS1 or LS6 unit, it's actually Nylon 6, a glass-filled polymer that is better suited to the vibration-welding process.
"After conducting numerous tests on our Superflow 600 flow bench to benchmark the LS6, LS2, and aftermarket manifolds, it was determined that the one fatal flaw of the LS2 design was that it allowed a minuscule amount of air to leak internally past the welds," says Incaudo. "As the combined head- and intake-flow requirements increased on modified engines, the problem was amplified, especially in the upper rpm range."
While it might be tempting to simply seal all of the leaking welds, welding the seams for a leak-free fit is actually quite difficult. Furthermore, the potential for failure when modifying the manifold using polymer-based adhesives is unacceptably high. "Rather than 'repair' the manifold, we developed a porting program that will flow more air, thus raising the power potential to levels typically seen only on high-dollar aftermarket intakes," says Incaudo. "On stock applications we normally see 5-10hp increases, with up to 20 hp available on engines with ported heads, higher-lift cams, and free-flowing exhaust."
Sold on an exchange basis, the ported LS2 intake retails for $300 shipped and carries PN VMax LS2 Port. For enthusiasts who need to purchase a new stock manifold, GM offers the LS2 unit under PN 89017648 for $421.61.
Follow along as we provide an overview of this stealthy, budget-friendly modification. Once that's done, we'll swap a ported manifold onto a stock, six-speed-equipped '06 C6 and gauge the results on a chassis dyno.
Although the LS2 intake manifold...
Although the LS2 intake manifold closely resembles the LS1/LS6, it's a three-piece unit that is vibration welded together. All LS2 manifolds have a 90mm throttle body opening and are set up for electronic throttle controls.
We'll use this previously...
We'll use this previously disassembled LS7 intake for illustrative purposes. The lower section is in the middle, the center section is on the left, and the upper section is on the right. Only the junction between the upper and the lower sections is welded during assembly; the center section is clamped in between.
Note the large 90mm throttle-body...
Note the large 90mm throttle-body opening and the sealing surface along the entire outer edge of the manifold's lower section. This area isn't welded but rather relies upon tight tolerances to seal.