Larry Shepard and his bunch discovered the five blade fan moved more air because it breaks the air up more since the blades are offset. Similar to the external fans on a GM alternator. Each blade is a different size. If you've ever looked at one, you know what I am talking about. The Mopar fan achieves the same effect since it's blades are offset. I'm no physicist, but it makes sense. I have actually proven it. I replaced a seven blade symmetrical fan with a five blade non symmetrical MP fan and the car ran cooler. Some people argue that a clutch fan cannot move more than a fixed blade, but that's false. The MP viscous fan is thermostatically controlled. It has a bimetal spring on the front that expands as it heats up. The fan can and will achieve 100% lockup under a heavy load as temperatures increase. The advantage they have is, they don't ALWAYS move the most air they can as the clutch allows slippage which saves horse power and increases mileage. It also reduces wear and tear on the water pump. Those old guys weren't stupid.
