In "LS1 Power Plan" (HPP Aug.-Oct. '08), our subject '00 WS6 T/A registered 381.1 rwhp and 365.8 lb-ft of torque, having gained an impressive 62.1 hp and 36.5 lb-ft. That "cam-only" configuration was both powerful and well mannered on the streets, and it put down a 12.79 e.t. at 109.59 mph to back up the dyno numbers.
To further separate the car from the crowd and generate more than 400 rwhp, the next stage was a "heads/cam car." Research for a set of higher flowing LS1/LS6-style cylinder heads that would fit with the stock LS1 bore led to myriad choices, both in factory- and aftermarket-based products. Adding real-life family budgeting, however, eliminated much of the aftermarket cylinder-head offerings. Luckily for the enthusiast, there are budget-friendly alternatives in ported factory heads, which led us to Texas Speed & Performance and Precision Race Components (PRC), that suggested using its PRC 220cc 5.3L Stage 2.5 heads.
According to co-owner Jason Mangum, "Those looking for a considerable gain in power for street/strip, small-bore LS series engines such as this, the 5.3L head offers it at a budget price. Along with raising the stock compression up to 11.00:1 to generate additional power, the head also performs almost identically to the costlier LS6 and LS2 castings. The key to making power with the 5.3 head is to revise the combustion chamber size and to replace the small stock valves (1.89/1.55-in) with oversize stainless steel ones. Although various sizes are available, the Stage 2.5 offerings come with 2.02-inch intake and 1.575-inch exhaust stainless valves."
Since the testing and development of the CNC program focused on maintaining a strong port velocity and a balanced intake and exhaust flow, the heads are well matched to the existing Comp cam (XER273HR, 224/230-degrees duration at 0.050 and 0.581/0.588 lift on a 114-degree lobe separation angle) and the supporting SLP LS6 manifold and Jet-Hot exhaust system with Corsa after-cat.
In addition to the heads, Jason strongly recommends that the small 26.4-lb/hr factory injectors be upgraded to a larger set of F.A.S.T 42-lb/hr injectors to ensure they can supply the engine with adequate fueling. As well as the increased flow rate, the F.A.S.T. injectors feature a wide 30-degree spray angle for superior fuel atomization and state-of-the-art technology to improve injector opening times and ensure crisp throttle response. Jason says, "The F.A.S.T. high-impedance injectors are high-quality and, unlike some other brands on the market, very easy to tune to achieve excellent idle-quality and low-rpm response."
After picking up a set of bare PRC Stage 2.5 heads (PN 199-PRC2.55.3) for $1,000, we swapped over the Comp Cams 921 double springs and titanium retainers from "LS1 Power Plan" and took you through the installation of the PRC Stage 2.5 heads in Part I.
Follow along as Matt Garzonie at Real Performance Motorsports in Lewisville, Texas, wraps up the installation of the PRC head package and replaces the factory fuel injectors with the F.A.S.T. ones. Once complete, Harold Baker's automatic-equipped '00 WS6 T/A will be retuned by Brian Lohse and unleashed on RPM's Dynojet chassis dyno. After documenting the results from the dyno session, the T/A will be strip tested at San Antonio Raceway in Marion, Texas.
 Since the stock injectors...  Since the stock injectors were already pushing up to 104-percent duty cycle at the end of the quarter-mile, a set of F.A.S.T Precision-Flow 42-lb/hr fuel injectors (PN 304208, retail $656.91) was supplied by the Comp Performance Group. Though the injector is rated at 43.5 lb/hr, at the LS1 fuel pressure of 58 psi, the injector flows a whopping 48 lb/hr, more than enough to support up to approximately 605 naturally-aspirated horsepower. |  PRC's package includes oversized...  PRC's package includes oversized Rev 2.02/1.575-inch stainless valves. |  Priced at an affordable $1,199.99...  Priced at an affordable $1,199.99 (PN 199-PRC2.55.3), the PRC Stage 2.5 heads feature new GM 5.3L aluminum cores that are CNC ported to flow 312 cfm on the intake and 234 on the exhaust at 0.600 lift. PRC sells the ported Stage 2.5 heads without valves for $1,000. |
 Customers have their choice...  Customers have their choice of "Stage" porting and either PRC or Comp Cams (shown) valvesprings. |  After installing the heads...  After installing the heads and exhaust system, the T/A was lowered, and the dipstick tube, coil packs, and plug wires were installed. Since the SLP LS6 intake manifold had previously been removed, it was placed on a clean surface and the two 10mm bolts on each side of the manifold that retain the injector rail were removed. Firm upwards pressure was applied, allowing the fuel-rail assembly (injectors and fuel rail) to come out as a unit. |  The fuel-injector rail was...  The fuel-injector rail was turned over, and a flat-bladed screwdriver was used to remove the clip that holds the injector in the rail. The process is repeated for the remaining seven injectors. (Before beginning the installation of the new ones, ensure that the lower O-ring seals on the spray tip end of each injector are removed.) |