PRC Stage I Heads
Next up was a set of PRC Stage I heads. The Stage I heads are based on new LS6 castings (PN 199-PRCLS61 retails for $999.99 each) and are CNC-ported to achieve 310-cfm flow on the intake, while retaining the factory valves and LS6 valvesprings (capable of .550 lift). The head was designed to utilize the stock combustion chamber and valve sizes of the LS6. Texas Speed & Performance suggested testing the LS6 version of the Stage I head because of the casting's popularity with enthusiasts, especially for naturally aspirated applications. According to Mangum, "The 64.7cc chambers yields a compression ratio of 10:9:1 when utilizing a .040-inch Cometic head gasket. Optioned with our performance valve job and optional PRC Gold double valvesprings we feel that the Stage I head offers a tremendous value." For people who will run over a .550 lift but don't need a spring capable of .660 lift, COMP Cams' 26918 beehive valvesprings can be added for $150. A replacement set of Texas Speed & Performance chromemoly pushrods (PN 25-7350, retail $109.99) in a 7.350-in size are used to compensate for the .005 of head milling performed to ensure a flat sealing surface.
After a quick swap to the PRC Stage I heads, the engine was warmed up to 165 degrees while Jason edited the tuning files to put in an additional 2 percent fuel down low and 1 percent over 5,800 rpm. Timing was locked at 26 degrees as in the previous tests. Once the initial dyno run was complete the engine responded with peak horsepower of 525.1 at 6,500 with 462.1 lb-ft of torque at 5,200. That's a 43 horsepower gain from cylinder heads alone. But wait, the engine's air fuel ratio registered between 12.6 and 12.8 between 3,000 and 6,500, which is a bit rich for the target of 13:0:1. Rather than edit the PE tables again, this time the timing was bumped up to 29 degrees from 3,200 rpm up through the redline. Would the extra timing bring more power and achieve the targeted air fuel ratio? In a word, yes. Horsepower jumped to 529.5 at 6,600 rpm, while torque nudged up slightly to 464.3. The air fuel averaged just a bit over 13.1, which led Jason to conclude, "The extra 3 degrees of timing really helped out the cam's power production. Not only did the peaks come up but the average horsepower (398.4) and torque (431.7) jumped by 6 hp and 2 lb-ft of torque. A total gain of 48 hp and 25 ft-lbs of torque were achieved. Based on the positive results of adding timing, Jason says "I believe the cam only combination would have benefited from additional timing as well. Hindsight is a great tuning aid but 5-10 hp worth of gains was probably on the table for the taking."
Bolt-Ons
Rather than stepping up the airflow in the heads by going to a Stage II or 2.5 head, this was the perfect opportunity to see how well the little 346 would respond to bolt-ons designed to increase airflow through the motor. According to Trevor Doelling, "The F.A.S.T. 90mm composite intake manifold [PN 111-54003, retail price $849.99] has consistently shown power gains when used on engine combinations where the airflow ability of the heads exceed 285 cfm." In addition, cubic inch displacement plays a significant role in the gains achieved with larger displacement engines benefiting the most. When combined with a Precision Tool and Machine (PTM) 90mm billet throttle body (PN PTM90, retail price $389.99) we routinely see 15-20 horse improvements, although the gains are greater when upgrading from an LS1 intake manifold. To supplement airflow, the stock LS1 75mm MAF is replaced with a specially calibrated SLP 85mm composite MAF (PN 33-23060, retail price $170.99). With the claimed ability to flow some 895 cfm (versus 805 cfm for stock), the MAF supports greater power potential." After removing the LS6 intake and all supplementary hardware such as the fuel injectors, the F.A.S.T. intake was installed, followed by the PTM throttle body and SLP MAF.
After repeating the warm-up procedures, the engine was loaded up and run to redline. Peak horsepower responded with 544.7 at 5,600, while peak torque came out to 472.8 ft-lbs. Gains attributable to the bolt-ons were 15.2 hp and 8.5 ft-lbs of torque. Interestingly enough, the air/fuel ratio registered at 12:7:1 at 3,300 rpm, but progressively fattened up all the way to 12:1 at 6,600 rpm. Clearly the target air fuel ratio of 13:1 wasn't achieved, so Jason once again went into LS1Edit and adjusted the tables. After a cool-down period, the engine was warmed back up to temp and pulled. When all was said and done, the air/fuel averaged 13:0 and the engine responded with additional power. Peak power jumped to 551.0 hp at 6,600 rpm and torque was also gained, showing 476.3 ft-lbs. Average horsepower registered at 403.3 with torque averaging 440.2 lb-ft.
Conclusion:
The little LS1--all 346 ci of it--is clearly a remarkable piece of engineering hardware. Any engine that can put out 400 hp with over 410 lb-ft of torque in stock configuration is phenomenal. Although it is commonly accepted that the SAE correction factors reward an engine in a minimal fashion as the heat increases and the atmospheric conditions degrade, there was no denying that this garden-variety used LS1 gained a phenomenal 151 hp and 65 lb-ft of torque while on its relatively short stay on the dyno. For a cam-only enthusiast looking to maximize the horsepower of their engine, the Magic Stick 4 is an excellent choice. According to Trevor Doelling, "The mainstay of our business is providing the enthusiast with the best value in terms of performance and quality for their hard earned pay. For owners that can afford to step up to a ported cylinder head, our Stage 1 series of GM casting cylinder heads are very economical yet they flow exceptionally well for a stock valve size. By using the smaller valves an enthusiast can not only save money but they can retain the factory piston to valve clearance." Let's face it, not everyone can afford to build a custom short-block or buy a set of heads designed to flow 350 cfm on their weekend race car. For the average enthusiast that has a stock-block car and wants reliable big power, the Texas Speed and Performance camshaft packages and Stage I heads offer a tremendous value.