Like it or not, cylinder head design is a subject that's very complex, and it's impossible to make it simple. Considering that no single component on an engine affects power output more than the cylinder heads, it pays to get educated. As a testament to the blistering pace of cylinder head development, the typical street/strip heads of today can oftentimes blow race heads of just 15 years past into the weeds. While the average hot rodder has benefitted greatly from the extremely competitive nature of the cylinder head business, the problem is that the people in the know aren't always willing to talk. After all, if you know something that gives you a leg up on the competition, why share your trade secrets for free? That's the question our sources asked us over and over again as we harangued them for info in order to compile this story. Fortunately, we somehow got them to divulge their secrets on topics ranging from port location to valve angles, and combustion chamber design, port shape, air speed, short-turn radius shape, to the importance of peak cfm.
Our daring cast of experts includes Tony Mamo of Air Flow Research; Kevin Feeney of Racing Head Service (RHS); Al Noe of Trick Flow; Tony McAfee of Dart Machinery; and Darin Morgan of Pro-Filer Performance, who's the former head R&D man of Reher-Morrison's Pro Stock engine program. As you gawk over that impressive list of all-stars, we'll take a moment to introduce you to CHP's newest department. The goal of our "How it Works" section is simple: tackle the intricacies of complex technical topics in a scope never before seen in a magazine article. Our two-pronged approach for accomplishing this is dedicating lots of space to accommodate meaty tech info and letting the real experts of our industry explain things in their own words. CHP is merely acting as the vehicle through which this otherwise-elusive information is gathered and disseminated. We're going so in-depth, that we only got to address a couple of the cylinder head topics we set out to answer before running out of space. Stay tuned for next month's issue, when we put the wraps on our cylinder head exposé. In the meantime, feel free to send in your suggestions on what tech subjects you'd like to see covered in "How it Works" in greater detail.
CFM and Velocity
Darin Morgan:
"Make no mistake, velocity is the primary variable in the design of the entire induction system. I often say that my job title should be Velocity Manager instead of Cylinder Head Designer. Air speed is 10 times more important than raw flow numbers. If you kill the velocity by 10 percent, you will kill almost 40 percent of the wave and ram energy that dynamically fills the cylinder! Raw airflow cfm is an important variable as well; it's just not as important. If you buy a cylinder head that is properly sized for a flow of 400 cfm and your engine is only asking for 350 cfm, you will not only fail to achieve the power potential that the 400 cfm would have given you, you will also fail to reach the power that the 350 cfm would have given you. That's because you killed all the air speed in the induction system. If your engine is asking for 350 cfm and you give it a properly sized cylinder head flowing 350 cfm, your airflow demand is matched and your air speed is matched. You then have a chance of achieving the power potential that 350 cfm can give you.