Manufacturing
"All AFR cylinder heads start as raw ingots of A356 aluminum poured at approximately 1,400 degrees. The mold it's poured into is maintained at a specific temperature as well. The casting process is a bit of a black art, and modern foundries are very specialized in what they manufacture. Once the casting is created, the next step is to drill pilot holes that allow us to accurately affix the castings to our CNC fixtures. Every machining operation except the actual CNC porting-such as drilling bolt holes, machining rocker-stud pads, and milling deck and flange surfaces-is done on one of our very large, five-axis, dual-pallet CNC machines. The twin-pallet machines work on a dozen castings at once. Before making their way to the smaller five-axis CNC machines for final porting, hardened seats and bronze guides are installed. Next, the dedicated porting machines handle the combustion chambers and intake and exhaust ports as well as some of the cylinder head engraving. At this point, the heads are pretty much finished but still need to still get a proper valve job, which is a very critical component of flow. The valve-job shape, diameter, and finish depth are all important. From there, it's off to the wash room, where the heads are finally deburred and thoroughly cleaned. Once cleaned, they are transported to our assembly room, where our operators carefully assemble the head with the correct springs, valves, and hardware. It's here that our final QC operator checks every head before it's placed in a box, confirming that the proper parts and machining operations have all been addressed."
Port Volume
Although some consumers equate larger ports with larger flow, AFR strives to keep port volume and cross section to a minimum to promote air speed and cylinder fill inertia. "If you think of air as a liquid, it's easier to understand how a faster column of air will have more energy and inertia to better fill cylinders, with far less reversion issues to boot," Tony explains. "This approach to cylinder head design is especially true if we are focusing on a product aimed more toward a street/strip application than for race use. A reasonably small port that has a strong airflow curve just makes for an explosive package that you need to experience to really appreciate. If you've driven lazy big-port heads and cam stuff all your life in your daily driver and step into a package I just described, you'd never go back." According to Tony, with the proper traction and gearing, that type of combination can yield quicker e.t.'s, since so much of drag racing is about what happens in the first 60 feet.
Porosity
Porosity in aluminum castings was more common years ago, and much of it was attributed to pour technique and speed, as well as how the mold was vented. "While the material itself can play a role, it was the actual pouring process that was a larger issue, as the mold must be heated prior to the pour," Tony says. "How the mold is designed also plays a role, and additional risers in the casting help provide a solid, nonporous surface. Technology and technique march forward, and while porosity may always occasionally rear its ugly head, most modern foundries have it figured out by now. Of course, in the event we machine a head that's porous, it's immediately flagged and pulled off the line so no additional machine time is wasted on that particular casting."