But before you pull out the checkbook, know this: it's not a completely direct swap, and in order to bolt a set of these heads to your engine, a few different constraints must be met. First, (and we're repeating ourselves a bit here), although the production L92 engine features a 4.065-inch cylinder diameter, these heads were designed to fit on bores as small as 4.00 inches so as to be compatible with the typical truck blocks already in production. So while these heads will go onto an LS2 or similar bore engine just fine, they will not bolt to an LS1 or LS6. In addition, before clamping these heads down, you will need to get a hold of head gaskets sized for a 4.065-inch bore. This is thanks to the L92's combustion chamber slightly overhanging the cylinder liner when installed on a 4-inch bore, and you don't want your head gasket lying out in the open and getting cooked. Probably most significantly, use of the L92 head requires a dedicated L76 intake manifold, as the high port floors mean a major mismatch with a conventional Gen III or IV intake. Also, depending on the size and style of your exhaust manifolds or headers, you'll need to keep an eye on exhaust port matchup, thanks to the L92's somewhat taller port. Finally, though your existing pushrods can be reused, you'll need to grab a set of offset inlet rockers (GM PN 12569167, less than $10 a piece); although happily, your stock exhaust rockers can be reused. With the above facts in mind, you should be able to bolt a set of L92 heads atop your stock short-block and reap the benefits of huge flow.
Conclusion
Just so you don't think we're operating in a "We Love L92" vacuum here, some comparisons to other head options are in order so as to give some perspective on what all the fuss is about. At around $800 total for a pair of assembled L92s, you're talking less than a third of the price of assembled LS7 heads-and only a few dollars more than what GM gets for a single assembled LS6 head. As far as aftermarket ported castings go, even the lowest of the low end of the Gen III/IV head spectrum will sell for around $1,000 a pair, and the vast majority of these won't even come close to the flow of the L92. High-end aftermarket units-especially those based off of aftermarket castings-can be triple the price of the L92 or more.
Even when factoring in that you'll need to spend a few hundred dollars on an L92-compatible intake (see the L92/L76 story elsewhere in this issue) as well as a few bucks more on any other necessary goodies like offset rocker arms and stronger springs, you still should be way ahead of the game on price point. Terrific flow for low dough-what a deal! Look for plenty more coverage and engine builds with these heads in the coming issues of GMHTP.
 Up close and personal with...  Up close and personal with the original and newer C5R intake ports, we note that the later design has a markedly smaller cross-sectional area (right). This is not a design improvement by any means; rather, it was mandated in a vain attempt to lessen the beating on other manufacturers in the American Le Mans racing series. According to GM engineers, the L92 and LS7 both took their cues from the original C5R head before such restrictions were put in place; nevertheless, it's clear the rectangular-port design remains all in the family. |  Probably the most obvious...  Probably the most obvious difference between the older and newer C5R designs lies in the combustion chamber, with the newer style (right) lacking much of the open contours and features of the original, which presumably interferes with cylinder mixing and flame travel. |  Lying side by side with the...  Lying side by side with the newer-style C5R head (left), it's clear that the L92 chamber got its racing heritage before the rules-mandated redesign took place. Look for the L92 to appear under the hoods of many a street and race car in the years to come! |