The solution is to reduce the head diameter to 2.05-inches, the maximum size that will work with the stock seat inserts. Superior’s Fred Simpson uses a carbide-tip cutter and feeds the cutter into the valve head by hand. He says: “The only tricky part is finding the right feed speed. The stainless material doesn’t always cooperate. Go too fast and the cutter chatters, too slow and the carbide tears the metal, leaving an uneven, scarred surface. Your ears are as important as your eyes in making a good cut.” A steady spray of chloride-based Petrochem Microfinish cutting lube from Champions Choice helps things go smoothly and prolongs cutter life.
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| As the valve head diameter is reduced to 2.05-inches, the thickness of the valve margin grows by 0.020 to 0.030-inch. This is a good thing. Not to be confused with the valve face – that’s the circular region that seals against the head – the margin is the transitional area between the end of the face and the beginning of the valve head – indicated here by the calipers. Generally speaking, a thicker margin on an intake valve improves flow. Fred Simpson explains: “The thicker margin serves as a directional aid to help the flowing intake gasses move more efficiently past the unavoidable obstruction caused by the valve head.” It’s a nice side benefit of the diameter reduction process. Notice the thicker margin on the valve after head diameter reduction work (right). | The stock 45-degree LS1 valve seats must be re-ground to match the larger valve head diameters. The pen points to the new valve seat’s placement on the outermost edge of the steel seat insert. Fred says the big valve swap is good for a 7 to 12 percent more intake port flow on an un-altered seat. Sharp eyes will notice that some contour work has been performed to merge the seat insert into the port. Though not mandatory, removing the now-unused valve seat insert material from the ID of the insert directly beneath the valve heads delivers an extra 3-8cfm per port. |
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