You understand the importance of getting a good air/fuel charge into the combustion chamber. It's not just quantity; it's also velocity and a homogenous air/fuel mixture. To get that, you have invested in quality heads and spared no expense to make sure you have the state-of-the-art when it comes to intake ports. But what about the rest of the tortuous path the air/fuel mixture takes from the carburetor boosters to the intake port in those expensive heads? What happens between point A and point B? Not good stuff if you aren't careful.
Good head porters and engine builders earn their keep by minimizing the losses that can occur in this area. The prime culprit, of course, is the intake manifold. No matter how you slice it, it is difficult to keep fuel in suspension in rapidly moving air as it makes the many turns required to finally get into the combustion chamber. Matching up the exits of the intake manifold runners to the entrances of the head's intake ports is usually the biggest improvement that can be made to improve flow in this area. Heads and manifolds are both created from castings, which can suffer from core shift. Plus, port locations can vary slightly from one manufacturer to the next. Ideally, these ports need to be matched up so the transition from manifold to head is invisible to the air/fuel charge as it travels toward the intake valve.
Port matching has been done for years, but the most popular method (reaching through the manifold to scribe lines where the ports do not match up) is not necessarily the most accurate. For one, more than half the time you are trying to scribe in areas you cannot see, and the human hand operating blind is not the most accurate tool when you are trying to stay within ideal tolerances of 0.015 of an inch. Another reason is with many manifolds, such as dual plane pieces, you cannot effectively reach the port transition with any type of tool.
Leagon's Racing Heads was founded by Roger Leagon, a longtime Winston Cup head porter. Roger is currently the manager of the cylinder head department at Dale Earnhardt Inc. While Roger spends most of his time in Mooresville working in DEI's engine department, his brother Ronald handles the day-to-day business at Leagon's in Blacksburg, South Carolina. Also helping Ronald are Roger's son Jonathan Leagon and Butch Roberts. The three agreed to show us a method of intake port matching that they feel is vastly superior to the old scribe-and-grind method.
Deck 'Em "The first thing you have to do before you can do anything else is know the deck height of your block," Ronald says. "Even though you are working on the interface between the manifold and cylinder heads, everything is affected by the location of the heads on the block. You have to have a block to mount your heads on before you can start port matching. Ideally, it's best if it is the same block, but it doesn't have to be. In this case, the block that we normally use here for Chevrolets has a 9-inch deck (from crank centerline). In this case, the block for these heads that we are working on has a 9.062-inch deck. We made up the difference with a couple of shims. You also have to take into account the extra height that the head gaskets will add once you put them under it."
Obviously, the best thing is to use the actual block you plan to use and have it already decked to the correct height. If you go this route, leave 0.002-inch extra material on the deck and then shave it off later to remove any scratches.
Likewise, you will also need to put shims on the head to duplicate the thickness of the intake gaskets. Ronald does not recommend using the actual intake gasket because it can interfere with your ability to determine where the ports do and do not match up. For example, if the gaskets are smaller than the port, it can be hard to see the edges of the intake port.