Over their lengthy production run, some later engines in the LS family tree got what is known as “two-corner” cooling, while earlier motors often used “four-corner” cooling—the distinction refers to the quantity and location of the steam vent ports on the LS cylinder heads.
Without going into a long dissertation on the subject of steam vents, the GM LS uses them near the top of the engine to help purge air bubbles in the cooling system. And those steam vents are darn effective too—so much so that GM engineers discovered that, instead of using a vent at each end of the cylinder heads, they could get by with just the two front steam vents for certain engine applications.
A few years into LS production, GM engineers not only eliminated the rear steam vents, they designed a new intake manifold that was introduced on the top-performing Gen. III LS, the LS6. Thanks to its improved airflow, that new stock LS6 manifold soon became a popular performance retrofit for earlier LS motors.
Problem is, the LS6 manifold (and some other aftermarket LS performance manifolds) was designed to work with the new two-corner steam vent system, and those earlier LS engines had four-corner cooling. That meant folks had to think of all sorts of ways to make the two play nice together.
The easiest method is to simply block off the ports in the back—and the easiest way to do that is with Summit Racing’s Coolant Crossover Delete Kit. Not only does the kit have everything you’ll need, it has a unique low-profile design that adds more clearance, while making it easier to remove the cylinder head bolts.