Small Block LS Engine Dyno Testing Part II - Big Power, Small Budget

Next, the Texas Speed/Precision... 

   

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Next, the Texas Speed/Precision Race Components L92 heads (see Sidebar) are mounted over the dowels, and a set of optional ARP hex head bolts (PN 46-134-3610; retail $99.99) are lubricated and threaded in. These heads have a total of 15 head bolts with 10 larger bolts located in the center and bottom of the head and 5 bolts at the top. Head bolts 1-10 are torqued to 75 ft-lb in sequence from the center outwards, alternating sides. A second pass takes them to 85 ft-lb. The five head bolts on the surface closest to the intake valley are torqued to 23 ft-lb alternating side-to-side, working outwards. For extreme forced-induction or nitrous use, Texas Speed offers ARP's Pro-Series 12-point head studs (PN 46-234-4317, retail $247.99).

PRC's ported L92/LS3 heads paid dividends with peak horsepower of 630 at 6,400 rpm and torque of 570 lb-ft at 5,200 rpm. Horsepower and torque gains were seen across the rpm range with averages of 12 and 11.5, respectively. Horsepower at the peaks jumped by 28 but torque gains were a more modest 9 lb-ft. The real story lies in the torque gains between 5,300 and 6,500 where they started out at 10 lb-ft and ramped up to 20 lb-ft. Neither torque nor horsepower suffered at the lower end of the rpm range.

The final test was comprised of the cam upgrade and TSP's own 100mm MAF, resulting in a staggering 641.2 hp at 6,400 rpm with 578.5 lb-ft. of torque at 5,200. Average horsepower and torque rose by 6.6 and 6.3, respectively, while the peak horsepower jumped by 10.9 with torque peak gains of 8 lb-ft. Although the peak and average gains were modest, the larger cam and higher-flowing MAF started to pick up almost equal amounts of power and torque from 4,900 rpm to the redline without sacrificing low-end power.

PRC Ported Cylinder Heads
L92/LS3 heads receive porting to the combustion chamber along with the intake and exhaust ports. The "rectangular"-port L92 head is patterned after the LS7 head but unfortunately also suffers from the same exhaust-flow deficiency. A shot inside the CNC machine shows the "D"-port-style exhaust port being thoroughly massaged. Although not shown, the PRC combustion chambers are available in sizes from 72 cc to 66 cc.

For enthusiasts looking to make big power at a budget price, TSP's offerings are right on target. LS2-equipped GTOs are prime candidates for an L92/LS3 head and cam package, since the stock bore size is 4.0 as is the L76-equipped G8. The only fly in the ointment on the G8 is the AFM, which requires a compatible aftermarket camshaft or a conversion to a non-AFM valvetrain in order to reap the full benefits of the blueprinted short-block or higher-flowing heads.

A GM LS2/LS7 valley-plate... 

   

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A GM LS2/LS7 valley-plate cover (PN 12570471) is used in the build rather than the L72 version that contains oiling provisions for the lifter oil-manifold assembly and active fuel-management (AFM or displacement on demand) collapsible lifters offered on the G8's L76 engine. Note the oiling provision block-off on the non-AFM-equipped valley plate.

Owners of LS1-based Firebirds and GTOs who are looking to build big power, remember that the L92/LS3 cylinder head requires a 4.0-inch bore, and with the maximum overbore that can be achieved on an LS1/LS6 pegged at 3.905 inches, it would be more cost-effective to bolt on a set of PRC Stage 2.5 heads (HPP, Oct. '08) unless you're in the market for more cubic inches and more power potential.

Cylinder-Head Flow
All flow numbers are quoted at 28 inches test pressure. Stock LS2 and L92 cylinder-head flow numbers are from the GMPP catalog. The GMPP catalog does not list flow numbers above 0.600 lift. Ported L92 cylinder heads were tested on Precision Race Components' SuperFlow 600 flow bench.

Included with the valley plate...        read full caption Included with the valley plate cover are new gaskets and 11 brand-new bolts. Once the bolts are loosely tightened, the cover is torqued to 29 ft-lb.

Rather than using a stock...        read full caption Rather than using a stock oil pump, TSP uti-lizes an LS6 oil pump (PN 25-12586665M; retail $139.99), which gets ported and its spring shimmed to increase the volume and pressure (10 psi) at all rpm levels. The porting provides extra flow to the main bearings, which is critical in motorsports. Note the pump's oil pickup is lubricated with Red Line assembly lube. To install it, the crankshaft bolt will be removed, the oil pump turned to the correct position and mounted, and the four oil pump bolts torqued to 18 ft-lb.

Once done, the engine is rotated...        read full caption Once done, the engine is rotated over, and a new O-ring seal is placed into the oil pump. The oil-pump screen tube is installed aligned with the correct crankshaft bearing cap stud, and the single 10mm bolt is torqued to 106 lb-in. As opposed to a traditional GM offering where the pickup tube is tack-welded to ensure that it won't dislodge, the thread sealant and integrated O-ring mount of the oil pickup are very well designed.