Click the picture for Intake...
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...
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.