Editor's Note: This story was assigned to contributor Jamie Meyer, who later took a position at GM Performance Parts-where the L92 heads and intakes are available from. While he does work with the GM components tested, every step has been taken to ensure that this story is as objective as possible, and no special considerations were made to produce the results seen here.
For the last few months, we've been pounding away on a stock LS2 engine at Livernois Motorsports looking for even more power than the factory delivers. As most GM High-Tech junkies know, the LS2 is a 364-inch, 400-horse, 400 lb-ft small-block GM V-8 that comes stock in the base Corvette, GTO, SSR, Trailblazer SS, or as a crate engine from GM Performance Parts. And, as complete as our last study was (see: LS2 Dyno Thrash, Part II: Head Shootout; January 2007), we still had one set of heads that we couldn't fit into our LS2 head shootout. Those heads are the L92 castings that come as standard equipment on the L92 engine, found in such production vehicles as the 2007 Cadillac Escalade in 403-horse form.
What makes the L92 head so special? It's designed straight off the LS7 head-the same head that offers you 505 horses when installed on the 427-inch LS7 in the current production Z06 Corvette. Not only does the L92 head design have a blue blood pedigree, but because they are being built for truck and SUV engines, GM Performance Parts has been able to obtain a large number of these heads for their power hungry customers. What that means is that the L92 head is cheap. Look for these things to sell for under $1,000-for a complete pair-assembled and ready to go. In fact, as you read this, the L92 head has just been released as PN 12582713.
The fact is that the L92 head is one of the most anticipated part releases of the 2006 racing season. Internet LS hotspots have been prophesizing about these heads for months with bold boasts of just how much potential is hidden in these super-affordable high-performance heads. To test the potential of the L92 head, we once again enlisted the help of Dan Millen and his Livernois Motorsports crew. We asked them to look at a stock LS2 with the stock heads versus the same engine wearing the L92 heads with the companion L76 intake (PN 12590123). That intake, by the way, is an interesting story in itself. As stated, the L92 heads can be found on various GM trucks and SUVs. Unfortunately, the "truck" intake for the L92 won't clear the hoods of too many production cars. The L76 intake has been enlisted for use with the L92 heads on several production cars in Australia wearing the Holden nameplate, and it's the perfect companion for a street car, packed with a hopped up LS2, wearing the L92 heads. Our sample L76 intake was quite literally the first one available in the states, and while it looks suspiciously like the stock LS2 intake, there are some very important differences. First, the L76 intake is designed to match up to the wider intake port configuration of the L92 intake. Secondly, the L76 intake has physically larger intake runners than the production LS2 intake. And, lastly, the L76 intake comes complete with a 90mm throttle body, fuel rails, and 39 lb/hr fuel injectors. All of that for around $500 makes the L76 the perfect companion for the L92 heads.
And, while we were swapping L92 intake manifolds, we got a chance to play with the killer new carbureted intake that GM Performance Parts has for these heads as PN 25534401. This allows a quick and easy way to get the L92 heads on an LS2 using your carburetor of choice. But Livernois wanted to take it a bit further. So, they built a prototype elbow and LS2 throttle body adapter for the intake so that you can use custom Livernois fuel rails (yes, there are injector bosses on this GM Performance Parts intake) and the stock LS2 fuel injectors. This allowed us to compare both intakes with the L92 heads using the same fuel system and throttle body. Now, we were getting excited! Testing Parameters For this test, we wanted to hone in on the heads working with the two different intakes. Assuming that anyone who was swapping heads would also be changing the cam, we installed the Livernois Motorsports Stage II cam that specs out at 232/236 @ .050, .600 lift on a 112 lobe separation angle. The valvesprings were also upgraded to support the .600-inch lift numbers on both the stock LS2 heads and the L92 heads. On the engine dyno, each combination was tested with BP premium pump fuel, 60 pounds of fuel pressure, Kook's long-tube headers, and a FAST throttle body. All tests were performed on the Livernois Superflow 901 water brake dynamometer, which is good to 2,000 ft-lbs. The Livernois Motorsports dyno cell is temperature controlled, and it was maintained at 68-70 during each test. Our goal was to keep the air/fuel ratio as consistent as possible from 12.5-12.8 for all tests.
 The hot news out of GM Performance...  The hot news out of GM Performance Parts is the release of a group of affordable, high-performance parts based on the LS7 design. The L92 heads (off of the truck and SUV 6.2-liter engine); the L76 production car fuel injected intake; and the carbureted L92 intake are the result of the technology. |
 The amazing new L92 head is...  The amazing new L92 head is a truly affordable high performance head that makes 500-plus horsepower out of a small-block very easy. The L92 heads are the "truck version" of the LS7 Corvette head. They feature a revised 70cc combustion chamber, massive intake ports, and a highly efficient exhaust port. |
 Valve sizes are 2.16-in intake...  Valve sizes are 2.16-in intake and 1.59-in exhaust. We had heard rumors that they flow 330 cfm out of the gate and over 360 cfm with only a valve job. Sold complete from GM Performance Parts as PN 12582713, they go out the door complete for less than $1,000 a pair! |
 This was the most rare piece...  This was the most rare piece of LS equipment in the country at the time these pictures were taken. The highly hyped L76 intake has been borrowed from a production Holden V-8. The L76 intake or PN 12590123, is what you need to match the L92 heads to your 6.0-liter Gen III/IV. |
 It is sold complete with injectors,...  It is sold complete with injectors, fuel rails, and a 90mm throttle body from GM Performance Parts for around $500. |
 Offered as PN 25534401, GM...  Offered as PN 25534401, GM Performance Parts has just released a new intake manifold that allows you to use a carburetor on your L92-headed LS2. The intake also contains injector bosses for fuel injectors-something that Livernois Motorsports took advantage of during the course of our testing. |