If Obi-Wan Kenobi was a cylinder head designer, he'd have a Haas five-axis CNC machine in his basement. Although his Jedi starfighter clearly makes use of a propulsion system much more advanced than a mere internal combustion engine, from a technological standpoint, the analogy is entirely appropriate. The capabilities of a modern CNC machine represent the pinnacle of cylinder head design. Think of them as Xerox machines, but for cylinder heads, that replicate intricately contoured ports and combustion chambers by whittling away metal. Only those who have spent countless hours porting cylinder heads by hand can fully appreciate what's possible with a CNC machine, and Judson Massingill of the School of Automotive Machinists is one of those guys. The school has recently added CNC courses to its curriculum, so the timing was perfect for us to drop by and get educated. With the help of instructors Jonathan Waitt and Andrew Bishop, the crew at SAM walked us through the entire process from hand-porting, to digitizing, to creating the final product on the five-axis machine.
All the technology in the...
All the technology in the world isn't worth squat if you start out with a poor set of heads. As such, the first step in the CNC process is some good old-fashioned hand porting. With symmetrical heads, where every port and chamber from cylinder to cylinder is the same, only one set of ports needs to be designed by hand. With siamesed heads, such as 23-degree small-block Chevy castings, two sets of ports must be designed. SAM students and instructors coaxed 460 cfm out of the prototype port and chamber on these Edelbrock Victor LS-R heads.
Although it's impossible to become a professional machinist by simply observing experts go about their business for a day, watching the CNC process up close is pretty darn cool. Biological creatures are simply no match for the port-to-port consistency and time savings CNC machines offer. "Between the digitizing probes, scanners, computer software, and the CNC machine itself, it really is like Star Wars technology. When porting a race head, you can easily spend two weeks designing one intake port, one exhaust port, and one combustion chamber," Massingill says. "What really kills you is trying to replicate those same ports and chambers seven more times for the remaining cylinders, and trying to achieve consistent flow from port to port. If you use snap gauges and molds to try to minimize port-to-port variation, it can add 10-15 hours of labor per head. Likewise, the short-turn radius is very difficult to get right, as slight variations in its shape will dramatically affect airflow. Even the best porters in the world can't get the short-turn the exact same every single time. The more complex the shape of a port-such as having a slanted port floor-the harder it is to match by hand."
The challenges of traditional hand porting are all but eliminated with a five-axis CNC machine. "On heads with symmetrical ports like the LS1, you only have to design one set of ports. The CNC machine can then make perfect copies of those prototype ports for the other seven cylinders in half a day whereas if you ported a set of race heads by hand, that process would take you months," Massingill says. Thanks to continual advances in CNC technology, port accuracy is phenomenal as well. "Just a few years ago, the goal was to get a CNC'd port to flow within 5-10 cfm of a prototype port. Now, you can get a CNC'd port to flow within 1 cfm of the prototype port."
Just like the fastest car doesn't always cross the finish line first, however, it takes a highly skilled machinist to get the most out of a CNC machine. As its name suggests, Computer Numerically Controlled machining operates using lines of numeric computer code. With the assistance of digitizers, it's the machinist's job to write complex strings of code that tell the CNC machine how to rotate around its axes, and where and how much to cut. To help its students meet these demands, SAM's CNC curriculum includes eight separate classes totaling 541 hours, over half of which are dedicated to hands-on training in the lab. During our visit, Massingill and company were hard at work porting a set of Edelbrock Victor LS-R heads for a 3,000hp drag car projected to run 6.70s at 220 mph in the quarter-mile.
The Victor LS-R heads are...
The Victor LS-R heads are a full-race design with peanut-sized ports and no real combustion chambers at all. While they give professionals tremendous flexibility in designing ports, they also require tremendous skill to properly shape. That means more room for error when porting by hand, which makes a five-axis CNC machine an invaluable tool in this type of application.
Haas Automation offers over...
Haas Automation offers over a dozen different models of five-axis CNC machines. Prices start at around $100,000, and they can be optioned with an assortment of tool magazines, chip removal systems, fixtures, and tables. SAM uses a state-of-the-art Haas ES-5-4T unit.
A five-axis CNC machine can...
A five-axis CNC machine can be used to cut things as simple as header flanges, or complex hunks of metal like blocks and cylinder heads. Consequently, Haas offers a number of different rotary tables in different shapes and sizes. A rectangular table works best for cylinder heads, and Haas makes fixtures to hold them in place as well. The table itself moves in three different axes: from left to right along the X-axis; a full 360 degrees of rotation along the B-axis; and up to 100 degrees of rotation along the A-axis, which runs through the centerline of the A-stand pivot point.