Peer under the hood of the fast cars at the strip or the local burger joint and you'll see the AFR logo etched into more than a few cylinder heads. Racers demand proven performance, so it's no coincidence that many of them turn to Airflow Research for their cylinder heads. Almost forgotten due to the company's overwhelming success in the street/strip arena is its decorated history in the most competitive ranks of professional racing. Over the years, AFR has powered top drag racers such as Bill Jenkins, Warren Johnson, and Bill Glidden to the winner's circle. Likewise, NASCAR legends Richard Petty, Darrel Waltrip, and Cale Yarborough all racked up multiple championships thanks to AFR cylinder heads. In other words, these guys make some darn good stuff.
Unlike other pack leaders of the industry that prefer to stay mum, AFR has never been shy about sharing its expertise with the public. The company's head R&D man, Tony Mamo, visits popular online forums on a daily basis. In addition to battling online myth-spreading with decades of head-porting experience, he encourages consumers to independently flow-test the heads they purchase and challenge the veracity of manufacturers' claims. His candid and unorthodox approach has earned him a reputation as one straight-shootin' SOB, so we're giving him the space to do what he does best: tell it like it is.
"The first step in designing a new cylinder head is to clearly define the direction and goals of the product. For our Gen III head, we wanted to produce a more efficient cylinder head that would make significantly more power but retain the factory port locations and valvetrain geometry. However, keeping everything in the stock location poses a greater challenge in port design because you're not working with any inherent advantages such as a raised intake floor, taller exhaust port, or raised intake roof. In the case of our BBC product, we decided to raise the exhaust port height to help facilitate a port design capable of exhaling enough flow to cover the much improved intake port. This would have been impossible without raising the port, as the height of the factory exit simply makes for too sharp of a turn, and no matter who designs the port, the laws of fluid dynamics would simply never allow a substantial amount of airflow with that sharp a bend."
Gen III cylinder heads flow exceptionally well due in part to their extremely flat valve angles, but Tony feels that too much emphasis can be placed on valve angles. "I'm certainly not going to say a flatter valve angle isn't advantageous, because it is, but the chamber design itself, the port design, the valve job, and the profile of the valve will have a far greater impact on flow," Tony says. A flatter valve angle doesn't guarantee more flow or additional power. It's the package as a whole that must be taken into consideration. Port architecture and location are much more important than valve angle. Much of the airflow benefit of moving from a 23- to an 18-degree head is attributable to better port geometry and layout. "Instead of a 90-degree turn in the intake port, an 18-degree head has a near-straight shot to the intake valve in addition to a higher intake floor, a raised port roof, and much larger valves; it's just a completely superior port layout on top of the fact that it has a flatter valve angle and better chamber design. Another factor to consider is the point of diminishing returns. The factory LS1 15-degree valve angle is already an extremely flat valve angle, and moving it a few degrees flatter doesn't have nearly the same impact as it would in an application that started at, say, 23 or 26 degrees like the old-school SBC and BBC, respectively."