Hand grinding the intake runners may be the first thing many racersthink of when the subje
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 you make any measurements you take intoaccount the thickness of
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 pen light as he checks to see how well thecommon walls match
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.
"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."
The wall of the runner in this shot extends wider than the intake portof the manifold--exa
Obviously, the best thing is to use the actual block you plan to use andhave 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 laterto remove any scratches.
Likewise, you will also need to put shims on the head to duplicate thethickness of the intake gaskets. Ronald does not recommend using theactual intake gasket because it can interfere with your ability todetermine where the ports do and do not match up. For example, if thegaskets are smaller than the port, it can be hard to see the edges ofthe intake port.
A scribe line (arrow) marks our good wall. This line will be ourbaseline for all the other
"Intake gaskets normally come in various thicknesses, so even though youneed to decide what thickness you plan to run, you can also use thatadjustability to help line up the manifold," Ronald adds. "For mostheads, they offer gaskets with 0.030-, 0.045-, 0.060-, 0.090-, and0.120-inch thicknesses. We usually start out with a 0.060. So say thefloor of the manifold is hanging down. You can thicken up the gasket tobring the manifold up and raise the floor of the runner to match theintake port instead of trying to add material to the manifold."
Line Up and Measure Down
Once the heads are bolted in place at the proper height and shimmed forthe head gaskets, paint the flanges of the manifold with machinist's dyeand place the manifold between the heads. You can use the bolt holes forinitially lining things up, but this will be the last time you will payany attention to them. The priority is the ports: If the bolt holes areout of line after you complete the port match, you can mill slots so themanifold will bolt into place.
Jonathan Leagon uses his baseline wall to find the dimensions for therest of the ports. By
Make sure the manifold is all the way down (you may want to hit the topof it with the flat of your hand to make sure it is properly seated) andcheck to make sure the manifold end rails have some clearance underthem. If they hit the block, it will keep the manifold from seatingproperly. The solution is to either go with a thicker intake gasket ormachine the end rails down some on a mill.
First, check that you have either the floor or ceiling of the port matchup on either bank. With luck, you will get either the floor or ceilingto match up properly on both sides. If not, you can try different intakegasket sizes to move the manifold up (thicker gasket) or down (thinner)in relation to the heads. Because most of the air/fuel charge flowsalong the ceiling of the port, Leagon's usually prefers the roofs matchup.
Next, slide the manifold forward and backward, checking to see where thecommon walls match up. Common walls are the narrow walls that separateintake ports that run side-by-side. The other wall of the port isgenerally called the pushrod wall, because it is the side closest to thepushrod. The common walls are straighter and generally easier to see andalign. Slide the manifold until you get the maximum number of commonwalls to line up. The best case is all four common walls line up on bothsides; the worst case is only one side of one common wall will line upat any one time. This is OK, too. Pick one wall as your starting pointon each side, make a note of exactly which wall you are looking at, andpull the manifold back off the engine.
Leagon's achieves a true horizontal scribe for marking either the ports'roofs or floors by
Now, instead of a handful of scribes, you will need a straightedge, apair of calipers (usually at least 12 inches long), and a single scribe.Start by marking your good floor or ceiling with a line all the wayacross the flange of the manifold. Next, scribe the line that marks thegood common wall, again with a straightedge. Both of these scribed linesshould run right along the edge of the walls of the port we'll be usingas a reference port.
With these two locations (for each side of the manifold) marked, you canbegin the real work. Using your calipers, measure each intake port wallon the head and mark that location on the manifold flange. For example,the first dimension you will measure will be the opposite wall of thereference port. Measure that distance with your caliper (if the walls ofthe port are parallel, you know the perpendicular distance because thecaliper will be at its smallest reading), then find that same distanceon the manifold at the corresponding walls and mark it. If you want tofind the point that is the true perpendicular to the good wall, scribean arc with your caliper. The point on the arc farthest from the goodwall is perpendicular to that wall. Always make your measurements alongthe straight walls of the ports--never on the radii that transition fromthe floor or ceiling to the walls.
A milling machine can be used both to help lay out your port lines aswell as cut out mater
Mark all the port locations, first by measuring on the head and thentransferring those distances to the manifold. Always return to your goodport wall for measuring to another point. This is your constant. Now youcan see why you want to make sure you always remember exactly which portwall is your reference--both on the head and the manifold. When you arefinished, you should have all the port locations from the head mappedout on the manifold flange. Best case, the manifold runners line upclosely with your marks.
Cut and Try
On the top of the manifold, you want the opening to match the spacer youwill be using. Not
"Those scribed lines are your road map," says Jonathan Leagon. "When youbegin grinding, you want to work to those lines, but never grind overthem. If you do that, you lose your ability to gauge how parallel youhave the port walls, your maximum size, everything. A good rule of thumbis to have the manifold runner about 0.015-inch smaller than the intakeport all the way around. This is for several reasons: One, it gives youa cushion when you are porting and two, the worst thing you can do ishave the air and fuel hit a wall in the transition from the manifold tothe head, so keeping the manifold part a little bit smaller helps ensurethat doesn't happen."
Now it's almost time to start cutting metal, but before you do, makesure you have a cutter that is the right size. The determining factorhere is the radius that forms the transitions between the floor andceilings and the walls of the intake ports on the head. It is criticalthat the radius of the cutter you use matches the radius in the intakeports. The right cutter will automatically make the right radius in themanifold as you are doing your grinding work. Consider, for example, youare grinding out the floor of the manifold runner. If the cutter is toosmall, if you grind out the floor to your desired location all the wayacross, it will leave that radius too tight. If the cutter is too large,once you have ground out the floor correctly, the cutter has also eatentoo far into the metal that makes up the adjoining walls.
Click the picture for Intake Valve Specs.
The easiest way to match-up your cutter to the port radius is to paintthe radius with a little machinist's dye. Pick a cutter that looks aboutright, lay it in the radius of the port, and turn it by hand a fewtimes. If it cleans up all the dye, then you have the right cutter. Ifit leaves dye in the center of the radius, the cutter is too large. Ifit leaves dye on either side of the center, the cutter is too small.
Now, finally, it is time to begin grinding, but at Leagon's the work,even at this point, is still supplemented by machine. "On intakemanifolds, you start with the most critical part, the runner exit, andthen work your way to the top," Jonathan explains. "We have found that amilling machine helps us really get the port shapes dead-on for a coupleof reasons. The milling machine makes the work faster, but it also helpsus shape the ports better. Eventually, you are going to have to get inthere with a hand grinder, but whenever you can use a machine like thisit helps take the variable of the human element out a little more."
Click the picture for Exhaust Valve Specs.
Jonathan uses a digital readout on his mill to help determine hiscalibrations. Before cutting anything, he uses a pointer in the chuckand the instrument panel to make sure all his measurements line up. "Iwill use both the hand calipers and the readout on the mill to make suremy measurements are correct before I cut anything," he says. "That way Ihave a double redundant check.
Cutting is done only with a cutter of the correct diameter for thecorner radius. On the first port, Jonathan is very careful only to makeminimal cuts until he is sure everything matches up correctly. Becausethe manifold runners have so many curves, the mill is limited in itsusefulness.
"It allows us to make near-perfect runner exits but, because all thewalls are curved, we can't cut very deep," Jonathan says. "The insiderunners have relatively straight walls, so sometimes I can cut downabout an inch there, but in most places I can't get 3/8- to 1/2-inchbefore I start cutting too deep into the metal or run out of material tocut. But, the mill still does excellent work where it can reach, and itgives me a good foundation continuing on up the runners by hand."
Of course, this assumes that there are no restrictions on manifoldmodifications. Many racing classes limit manifold port matching to nomore than an inch (or less) from the bottom of the runners. In thatcase, everything becomes a game of give and take. You want thetransition from the manifold to the intake port to be as seamless aspossible, but you don't want to screw up the manifold runner in theprocess. In this situation, it becomes critical to find a manifold thatmatches up well to begin with and to improve from there really requiresa lot of experimentation on the flow bench and even the dyno.
Don't Forget the Gasket
So now you have perfectly matched your intake manifold to your cylinderheads, but what about the piece of material that gets pressed betweenthe two? "A lot of people don't give any thought to their intakegaskets," Ronald says, "but what if I fix you up a really nice head, andJonathan fixes you up a really nice manifold to go with it, and then thegasket that gets put on there doesn't match up right? It defeatseverything we've done and all that money you have just spent."
Fortunately, matching up the gasket to intake ports isn't a difficultjob. The first thing to do is secure the gasket to the head so it willnot move. Contact cement usually does the job well. Put a light coat ofcontact cement on the gasket, locate it on the head so the bolt holesline up, press it in place, and then leave it overnight to dry. In themorning, when the glue is dry, press clean shop rags into the ports anduse an Exacto knife to trim away any areas of the gasket that intrudeinto the port. Also, if you do have a sharp transition from the manifoldto the head because of porting limitations, you can take advantage ofthe gasket's thickness to help reduce that problem. Simply cut thegasket on a bevel to help reduce the transition angle between therunners. At best, this trick is a Band-Aid, but sometimes a Band-Aid isbetter than nothing.
The second chamber and its ports have been through Leagon's Stage IIprocess, which can be
If You Can't Beat 'Em...
We don't normally talk about cheating in the pages of Circle Track, butwhile working on this story the folks at Leagon's Racing Heads showed usa cylinder head that really caught our attention. This head has had itsNo. 2 combustion chamber ports modified and disguised in what RonaldLeagon will describe as the company's "Stage II process." We don't claimto be experts in this area, but it's one of the best jobs we've everseen.
"It's a tough situation to be forced to have to offer a product likethis," Ronald admits, "but there are so many series where we knowdrivers are racing against cheated-up heads. There are some racingseries that do not allow porting on the heads, and they do a good job ofkeeping that stuff out. But there are other series that say they don'tallow it--but if you are running by the rules you don't stand a chance.It's for racers that are in this situation that we offer this Stage IIprocess so they can at least be competitive."
The head Ronald showed us had one modified intake port while its brotherwas left original. The ports had almost exactly the same volume, but allyou had to do was feel with your index finger to know that the modifiedport was much improved. The shocking part was how hard it was to tellthe difference visually.
Naturally, nobody at Leagon's was eager to tell us the specifics on whatwas done to the head, but they did allow us to carry away a flow testcomparing Stage II versus stock intake and exhaust flow. Keep in mind,these numbers were obtained on Leagon's flow bench, but we have noreason to believe their numbers were doctored. For both ports, valveswere 2.020 intake and 1.600 exhaust, intake port volume was 200 cc andthe chamber volume was 64 cc. The flow numbers were derived at 28 inchesof water.