Looks pretty stock, huh? That's...
Looks pretty stock, huh? That's the point!
Though LS1-equipped '04 Goats were certainly stout, the bar was raised even further when GM rolled out the evolutionary Gen IV LS2 engine for the '05-'06 models. In addition to a host of improvements, the bore size was enlarged to 4.0-inches, resulting in an 18 cubic inch displacement increase to 364. Output was increased to 400 horsepower and 400 lb-ft of torque.
With innovation came other changes. The LS2 intake and throttle body are significantly different from previous GM LS1 offerings. While the '04 GTO LS1 engine carried an LS6 intake manifold and cable-operated 75mm throttle body, the LS2 debuted a new style of intake manifold and a 90mm electronically-controlled throttle body.
According to Pete Incaudo of Vmax Motorsports, "The LS2 manifold has a marginal increase in plenum volume over the LS6 and similar runner shapes optimized for the 6.0 liter engine. What changed, other than a 90mm throttle body opening, was the technology employed to produce the manifold. The Gen III LS1 and LS6 composite plastic manifolds were produced using a "lost core" plastic molding process that resulted in a single-piece plastic injected molded manifold."
The process involves the use of a low-melting temperature metal core, which is then loaded into a plastic molded tool, over-molded and then melted-out after the part is formed. Nylon 66 was the standard material used to produce the LS1/LS6 "composite manifold."
Pete continues, "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." Vibration welding, sometimes referred to as sonic welding in the industry, is simply melting the composite together after "vibrating" the materials to produce the necessary friction for a weld. Although the manifold material looks similar to an LS1 or LS6, the manifold is in fact produced using Nylon 6, a glass-filled polymer that is better able to be vibration welded.
The LS1/LS6 engines use a...
The LS1/LS6 engines use a "lost core" manufacturing process, which produces a one-piece manifold. Note that the throttle body opening is for a standard F-car 75mm throttle body. This manifold uses a traditional throttle cable bracket.
"In short," Pete says, "a miniscule amount of air is leaking internally past the welds, costing air flow and power in the process. Although in principle it may seem simple to seal all of the leaking welds on the intake, in reality, welding the seams for a leak-free fit is extremely difficult. The liability of repairing the manifold using polymer based adhesives is unacceptable.
"Rather than repair a manifold, we developed a 'porting' program that will flow more air through it, thus raising the power potential of the head and intake manifold combination to levels typically seen only on high-dollar aftermarket intakes. On stock applications, we normally see 5-10 horsepower increases with up to 20 horsepower on engines with ported heads, higher-lift cams and free-flowing exhaust."
Sold on an exchange basis, LS2 intake porting retails for $300 shipped (carried under PN Vmax LS2 Port). For enthusiasts who are looking to purchase a new manifold, GM carries the LS2 manifold (under PN 89017648), which retails for $421.61.
In addition to porting an LS2 manifold to increase the flow, additional power can be made by improving upon the stock LS2 90mm throttle body. Shaner Performance has been specializing in porting GM throttle bodies since '99. Its latest offering is the S2 series of ported throttle bodies for the LS2.
The throttle body has been extensively modified and includes boring out the main body's restrictive ridge at the leading edge of the throttle blades. Offered on an exchange basis or as a service to your original, the throttle body runs $125 shipped. LS1 and LS6 throttle body porting is also available for the same price, and a polished finish ($159) can be ordered.
 In contrast, although the...  In contrast, although the LS2 intake manifold closely resembles the LS1/LS6, it is a three-piece manifold that is vibration welded together. All LS2 manifolds have a 90mm throttle body opening and are set up for electronic throttle controls. |  For illustration purposes,...  For illustration purposes, an LS7 manifold that was already "separated" will be used. Other than having rectangular ports and a slightly revised port volume for the LS7 engine, the LS7 intake is constructed using the same technology as the LS2. The lower section is in the center, the center section is on the left, and on the right sits the upper section. The center section sits in the lower, and the upper section fits over and around the other two sections. Only the junction between the upper and the lower sections is vibration welded, thus the center section is "clamped" between them. |  Note the large 90mm throttle...  Note the large 90mm throttle body opening and the sealing surface along the entire outer edge of the lower section of the manifold. The area around where the intake is located has a sealing surface. When the manifold is vibration welded, this area isn't welded but instead relies upon tight tolerances to seal. |