The center section (lower...
The center section (lower plenum) of the manifold is placed into the lower section. Pete points out that the sealing surface directly behind the 90mm throttle body opening is challenging, from a manufacturing standpoint, to seal. Since the LS2 manifold isn't vibration welded internally, the stacking of minor manufacturing tolerances can lead to internal leaks.
According to Mark Shaner, of Shaner Performance, "The 90mm GM throttle body is more refined and better flowing than the Gen III offerings. By eliminating the air tubes and PCV from the throttle body and designing blade screws that do not protrude into the air stream, much of the flow disruption from prior years was eliminated. Additional flow is achieved by removing material around the entrance and exits of the throttle body blades. Due to the critical tolerances of the throttle blade's movement for idle control purposes, the porting work has to be very precise or else the car will not idle properly."
Now that you know the players and their products, follow along as we perform two stealthy power-increasing LS2 modifications, while flying under the radar of both the dealer and fellow enthusiasts. Before and after dyno runs will be completed to document the power increases.
LS2 intake manifold porting was conducted at Vmax Motorsports, and Shaner Performance ported an LS2 throttle body. Testing was conducted at Real Performance Motorsports of Lewisville, Texas, on an '06 GTO owned by Bob Cook, a CNC machinist from Allen, Texas.
| Dyno Results |
| Dyno | HP | HP Avg. | Torque | TQ Avg. | A/F Avg. |
| Baseline | 348.7 | 326.5 | 353.2 | 334.7 | 12.5 |
| Ported LS2/Ported TB | 357.8 | 332.9 | 363.0 | 341.2 | 12.5 |
| Power increase | 9.1 | 6.4 | 9.8 | 6.5 | 0 |
The center section contains...
The center section contains the lower portion of the intake runners. Pete notes that the upper section seals to the lower plenum between each intake runner. Any mismatch at these sealing junctions results in minor variations in port flow from one runner to another.
The upper plenum, or top section,...
The upper plenum, or top section, of the manifold has a corresponding sealing surface to the previously shown lower section.
The upper section is fitted...
The upper section is fitted and then vibration welded to the lower section. In the aftermarket, composite two-piece manifolds are available and, rather than vibration welding the assembly together, the upper and lower plenums use a traditional O-ring type gasket and fasteners for sealing. Other than higher cost, this type of "removable" top section allows additional porting access to engine builders.
A cutaway of a front section...
A cutaway of a front section of the intake runner reveals the joining line between the upper and lower plenums (aka upper and center sections). Since this press fit is not welded together, it is susceptible to a minor amount of leakage, which results in a reduced transfer of air, in both quantity and volume, to each of the cylinders.
Since the internal sealing...
Since the internal sealing of the manifold can't be addressed in the aftermarket, Vmax Motorsports came up with an LS2 manifold porting program to flow more air through the manifold. The runners are shaped using 1/2-inch and 3/8-inch carbide cutters, which are then polished with 60 and 240 grit roll sandpaper. Porting is accomplished using a Dumore straight handle grinder.
A close look at an intake...
A close look at an intake port reveals that, in addition to removing material in the port, the top and bottom of the runner entrances have received a significant rework. Note how the manifold joins in the runner.
On average, the initial port...
On average, the initial port width on a stock LS2 manifold averaged 0.94 inches, while the ported LS2 manifold averaged 1.051. As shown on the ported manifold, a "center" port measured 1.0455-inches.
After completing the intake...
After completing the intake porting and carefully replicating the porting template, attention turns to the 90mm throttle body opening where the focus is on the floor and roof, in order to transition the air back to the runners more smoothly. A careful measurement of the area directly behind the opening indicated that it was increased from 91.6mm to 94.8mm, after Pete's rework. Refer to the sidebar for flow bench results.
Let's take a quick look at...
Let's take a quick look at the factory LS2 throttle body. Carried under PN 12570790 and retailing for $477.22 directly from GM, this is an excellent factory throttle body. Rather than utilize air tubes to maintain proper idle characteristics, the LS2 throttle body has an intake air control (IAC) sensor and throttle body actuator motor that will electronically open and close the throttle blades a precise amount. One shortcoming, however, is the ridge at the leading edge of the throttle blades.