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 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.
All told, VMax's intake-porting regimen resulted in increases of 10 rwhp and 9 rwtq, all for only $300. Even better, most enthusiasts can perform the swap at home in less than an hour. Best of all, the ported manifold is completely stock-appearing and will fly under the radar of fellow enthusiasts...as well as the dealership.
"I am really impressed by the additional power gains that the ported manifold provides," says car owner Tammi Douglas. "The car feels more responsive around town as well as in the upper rpm range. Knowing that the manifold isn't restricting performance gives me confidence that additional modifications will yield results without having to invest in an aftermarket [unit]."
For C6 Z06 owners, VMax has been hard at work on a porting program for the LS7 intake. In fact, a fully ported LS7 unit should be available by the time you read this. For the stock-appearance purist looking for additional performance or anyone intent on having the most powerful C6 around, the need to purchase an aftermarket manifold just became less acute.
In addition to porting the LS2 manifold, VMax offers a ported LS2 throttle body that it recommends to enthusiasts who have made additional engine or tuning enhancements. "On stock applications, the ported throttle body will significantly improve low-speed responsiveness, but it really shines when additional modifications-like a free-flowing exhaust and a performance camshaft-are made," says Incaudo. Sold on an exchange basis under PN VMax LS2 TB, the throttle body retails for $150, shipped.
The factory LS2 throttle body bears PN 12570790 and retails for $477.22 directly from GM. Rather than utilizing air tubes to maintain proper idle characteristics, the LS2 unit has an intake-air control (IAC) stepper motor that electronically opens and closes the throttle blades. One shortcoming of this design is the ridge at the leading edge of the throttle blades.
Although it flows more air than both the 75mm LS1 and 78mm LS6 throttle bodies, the LS2 unit can be ported for even greater performance. VMax's changes include boring and blending out the restrictive ridge at the leading edge of the throttle blades, as shown here.
Flow Testing and Forced Induction
Our LS2 intake was flow tested at 28 inches of pressure using a Superflow 600 flow bench. A stock LS2 cylinder head was used initially to document the head flow using only the Number 6 intake port (Test 1). A stock LS2 manifold was installed for Test 2, and flow was again recorded on the Number 6 port with all other runners blocked. For Test 3, a ported LS2 manifold was installed and the test repeated.
Our results indicated that the low- and high-lift cfm numbers benefited the most. Although the cfm increases weren't substantial, intake-manifold porting isn't all about raw numbers. It also has much to do with the transition and quality of air. Pure cfm increases that decrease port velocity or disrupt flow are often counterproductive to hp.
"In forced-induction applications, the ported LS2 manifold consistently outperforms the LS6 and the popular aftermarket intakes during our test sessions," says Incaudo. "When pressurized, any internal leaking is eliminated, and the overall port volume and runner shapes of the LS2 manifold can perform as intended. On a recent session on a chassis dyno, we gained 20 rear-wheel hp-from 695 to 715-by swapping out an LS6 intake on a '03 C5 featuring our CNC-ported LS6 heads and running 15 pounds of boost."
Port and runner stall at 0.550" valve lift.