Wet flow testing allows a cylinder head designer to look at how the air/fuel mixture behaves when routed through a head and into the combustion chamber. The air/fuel mixture is much heavier and behaves very differently than dry air, so managing the mixture efficiently gives much better results than just increasing air flow will. Wet flow testing produces data that represents the operating conditions of an engine far more accurately than traditional dry flow testing.
Dart’s custom-built, computer-controlled wet-flow bench fills an entire workroom. Powered by three 50-horsepower electric motors, this amazing machine can flow 800 cubic feet per minute at a vacuum of 55 inches of water. (For comparison, the industry standard for dry-flow testing is 28 inches of water.) A nonflammable liquid with the same specific gravity as gasoline is injected into the intake air stream at a 13:1 air/fuel ratio. This liquid has a fluorescent dye that glows under ultraviolet light, allowing the flow bench operator to visualize the movement of the fuel as it travels through the port, valve and chamber.
“The wet-flow bench was originally intended to be a tool to develop our Pro Stock heads,” says Tony McAfee, who oversees Dart’s cylinder head R&D program. “But when we tested our production heads on the wet-flow bench, it was a revelation. We realized how dramatically we could improve the performance of every Dart head by applying what we’d learned in wet-flow testing”.
“One thing I look at,” says McAfee, “is whether a port design will maintain a constant air/fuel ratio.” Tests are made at a predetermined ratio, 13.7:1. But the wet flow bench also measures the actual air (in cfm) and fuel (in pph) being used. The air/fuel ratio with the most fuel makes the most power. Remember that the idea is to obtain a homogenous mix of air and fuel. With a better mix, more fuel is actually delivered to the combustion chamber, creating the potential for more power.
Wet flow technology was employed to create Dart’s line of Platinum cylinder heads and continues to be used in current research and development projects.