Hand grinding the intake runners...
Hand grinding the intake runners may be the first thing many racersthink of when the subject of intake port matching is brought up, it isactually the last of many important steps in the process at Leagon'sRacing Heads.
You understand the importance of getting a good air/fuel charge into thecombustion chamber. It's not just quantity; it's also velocity and ahomogenous air/fuel mixture. To get that, you have invested in qualityheads and spared no expense to make sure you have the state-of-the-artwhen it comes to intake ports. But what about the rest of the tortuouspath the air/fuel mixture takes from the carburetor boosters to theintake port in those expensive heads? What happens between point A andpoint B? Not good stuff if you aren't careful.
Good head porters and engine builders earn their keep by minimizing thelosses that can occur in this area. The prime culprit, of course, is theintake manifold. No matter how you slice it, it is difficult to keepfuel in suspension in rapidly moving air as it makes the many turnsrequired to finally get into the combustion chamber. Matching up theexits of the intake manifold runners to the entrances of the head'sintake ports is usually the biggest improvement that can be made toimprove flow in this area. Heads and manifolds are both created fromcastings, which can suffer from core shift. Plus, port locations canvary slightly from one manufacturer to the next. Ideally, these portsneed to be matched up so the transition from manifold to head isinvisible to the air/fuel charge as it travels toward the intake valve.
It is critical that before...
It is critical that before you make any measurements you take intoaccount the thickness of both the head and intake gaskets. Instead ofusing the actual gaskets, Leagon's will replicate their thicknesses withshims, which are easier to work around.
Port matching has been done for years, but the most popular method(reaching through the manifold to scribe lines where the ports do notmatch up) is not necessarily the most accurate. For one, more than halfthe time you are trying to scribe in areas you cannot see, and the humanhand operating blind is not the most accurate tool when you are tryingto stay within ideal tolerances of 0.015 of an inch. Another reason iswith many manifolds, such as dual plane pieces, you cannot effectivelyreach the port transition with any type of tool.
Ronald Leagon uses a flexible...
Ronald Leagon uses a flexible pen light as he checks to see how well thecommon walls match up between the intake manifold and cylinder head.Once you get one wall to line up (as well as either a floor or roof) youcan use that as a reference for everything else. Notice how the flangeat the bottom of the manifold does not touch the block. If it does, someof that flange will need to be milled off so the manifold will seatproperly. That gap is taken care of by either a gasket or bead ofsilicone.
Leagon's Racing Heads was founded by Roger Leagon, a longtime WinstonCup head porter. Roger is currently the manager of the cylinder headdepartment at Dale Earnhardt Inc. While Roger spends most of his time inMooresville working in DEI's engine department, his brother Ronaldhandles the day-to-day business at Leagon's in Blacksburg, SouthCarolina. Also helping Ronald are Roger's son Jonathan Leagon and ButchRoberts. The three agreed to show us a method of intake port matchingthat 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 knowthe deck height of your block," Ronald says. "Even though you areworking on the interface between the manifold and cylinder heads,everything is affected by the location of the heads on the block. Youhave to have a block to mount your heads on before you can start portmatching. Ideally, it's best if it is the same block, but it doesn'thave to be. In this case, the block that we normally use here forChevrolets has a 9-inch deck (from crank centerline). In this case, theblock for these heads that we are working on has a 9.062-inch deck. Wemade up the difference with a couple of shims. You also have to takeinto account the extra height that the head gaskets will add once youput them under it."