Story and photos by Steve Magnante
11/15/07

LS1 owners looking for increased port flow can take advantage of readily available oversize intake valves like those offered by Manley and other suppliers. The only snag is they feature 2.08-inch head diameters – which force the installation of larger valve seat inserts in the aluminum LS1 cylinder heads. The added expense and effort of the valve seat swap is a big turn-off that makes a minor surgery into a major one, and presents more than a few opportunities to screw up the heads.

To get around this, Joe Jill and the techs at Superior Automotive have come up with a solution that keeps the stock valve seat inserts in place. Superior simply takes Manley 2.08-inch intake valves and turn the heads down to 2.05-diameter so they are compatible with the existing OE valve seat inserts. You might ask, why not just get 2.05-diameter valves? None are offered at present, so this machining trick is the only way to fly. The result is an improvement in intake port flow of 7-12 percent, and there’s more on tap with basic hand blending.

Head diameter of the stock LS1 intake valve (left) is 2.00-inches. It’s an excellent valve for mass production, but represent a limitation in flow. The Manley 2.08-diameter valve (PN 11398) features swirl polishing and 0.012-undercut stems and is a popular upgrade, but the larger head diameter is just too big for the stock LS1 valve seat insert. If you tried to run the big 2.08 valve on a stock seat, the closed-valve contact face would extend off the steel insert and into the aluminum surrounding it.

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