GM Performance Parts - L92 Cylinder Heads - Wonder Head

Looking for a badass head, but don't have a lot of bread? Bargain build aficionados, your prayers have been answered: GM Performance Parts now offers the cylinder head straight off its 6.2L (RPO L92) engine used in the new Cadillac Escalade and GMC Denali-series trucks. This brand new mill-with its 4.065-inch bore, variable valve timing, and fuel-saving displacement on demand-is the showpiece of current GM small-block engine technology. But more importantly for all Gen III/IV enthusiasts, the L92's head flows so well, it'll offer bolt-on performance as good or better than many aftermarket CNC-ported heads on the market for a fraction of the price.

How is this possible, you ask? A head that costs comparatively so little may induce fears of the automotive equivalent of an Intel Celeron processor: are these defective, poorly performing castings that didn't come off the assembly line quite right? Or, perhaps they're a cheaped-out, skip-some-important-machining-steps version of a head GM already makes? Fortunately, none of these suspicions come anywhere close to the truth: in fact, the L92 is a top-quality, race-inspired unit that is so inexpensive simply because it's a high-volume production piece.

The photos you see here compare these new L92 castings to other Gen III/IV units GM has already brought to market; we'll note some of the similarities and differences between them in the captions. But what's most exciting is that the L92 is, by and large, an early version of the head that ended up crowning the Z06's 427ci LS7 engine. So in other words, this ain't your ordinary truck head!

How The L92 Came To Be
To get the skinny on exactly how these amazing heads materialized, we talked to some of the folks who know at GM. The story begins a few years back with what would be the LS7 engine program-a project that drew significantly from GM Racing's experience with C5R technology. For the Sixth Gen Vette's killer model to truly dominate the competition, higher-ups decided a minimum of 500 hp would be needed from the engine powering the next Z06. Unsure of what displacement it would take to achieve these numbers in a naturally aspirated application, GM engineers began the task of meeting this mark by designing prototype heads for somewhat smaller bore diameters than would eventually make it to production. Dennis Gerdeman, Cylinder Head Design Release Engineer for the L92, explains. "When the LS7 was first being developed, its cylinder bore was not 4.125 inches. We kind of grew into that diameter as we pushed the envelope further and further and learned more and more from the C5R guys. We finally decided that more cubes would be needed to meet the 500hp goal, and it's at that point that we divorced ourselves from the smaller bores and went down the path of what would eventually become the LS7 cylinder head-maximizing its airflow with larger valves, CNC porting, and other features." But fortunately the LS7 team's early efforts at a smaller-bore head would not go to waste: when orders came along for a small-block truck engine with a minimum 400hp, engineers realized that this early LS7 design could be tweaked to work quite well for truck and SUV applications.

Basic specs on the L92 combustion chamber are as follows: the chamber volume is 68.4cc, and it uses a honkin' 2.165-inch intake and a 1.590-inch exhaust valve. As such, don't even think about bolting one of these suckers to an LS1 or LS6: it'll need at least a 4-inch bore to work. (And though we've been assured that stock piston valve reliefs will work just fine with these heads, we can't promise the large valves of the L92 will work with every possible aftermarket piston: if that's your route, proceed with some caution.)

With its rectangular intake ports, the L92 appears more like a race head than those you'd find on most other Gen III/IV engines. But its price speaks otherwise: bare heads can be had for about $175 each (PN 12582714), and assembled heads for just shy of $400 each (PN 12582713). Note that included with the assembled heads will be LS1-type valvesprings, retainers, and locks-so if you'll be using anything but a stock-type cam, stiffer springs will be in order.