Reply to "Coolant tubes under the car"

The improvement to be realized by increasing the size of the plumbing, especially on the radiator outlet side, is based upon the principles of centrifugal pump operation. Coolant pumps are centrifugal pumps; such pumps do not have a linear output (i.e. flow) verses speed curve. The pump must rotate at a certain minimum speed in order to reach the point in which increases in speed result in increases in output. Below that speed the pump's output does not increase with increases in speed. The speed at which the pump's output begins increasing varies based upon the resistance to flow (i.e. head) at the pump's inlet and outlet. As the resistance to flow increases it requires a higher pump speed in order for the pump to enter that part of it's output verses speed curve in which increases in speed result in increases in flow. The Pump's maximum flow capacity shall also decrease as head increases.

Neither the OEM Ford coolant pump, nor ANY of its replacements, were designed to pump coolant over the distances it must be pumped in the Pantera's mid-engine application. The amount of head in the Pantera's cooling system caused the OEM coolant pump to drop lower in its output verses speed curve. The pump simply doesn't pump enough coolant at idle speed. Considering the nature of centrifugal pumps it should be no surprise that the lay-out of the Pantera's cooling system impinges upon the coolant pump's output.

Coolant pump output can be improved by 3 things:
• A pump with a different output verses speed curve (i.e. the Flow Kooler pump).
• Higher rotating speeds for the OEM pump (i.e. the SACC overdrive pulley).
• Less resistance to flow (i.e. larger diameter plumbing, fewer bends, bends with larger radius).

The rate of coolant flowing through the engine is restricted intentionally by Ford engineers by the singular square outlet hole in each cylinder head. Its been a long time since I measured one, but as I remember its more or less equivalent to a 3/8 inch diameter hole (or was that 5/8?). This is where the backpressure necessary to prevent boiling within the engine is created. These two small outlets are the reason I'm not too concerned about the diameter of the plumbing between the engine's outlet and the radiator inlet. I do not argue however that increasing the size of this plumbing would indeed decrease head.

Once the coolant flows through the radiator there should be as little resistance as possible for coolant flowing to the pump's suction. Why you ask? Simply because that is the parameters the pump was designed to operate within. The suction of the 351C coolant pump has a 1-3/4" OD hose connection. The radiator outlet of all Ford's V8 equipped vehicles was also 1-3/4" OD. In the Pantera the plumbing between the radiator outlet and the coolant pump inlet is 1-3/8" OD, which is obviously smaller than the designers intended. Considering the diameter and length of the radiator outlet plumbing it constitutes the most potentially severe "resistance to flow" in the cooling system's plumbing due to its impact upon the coolant pump's performance. Rubber hoses located on the radiator's outlet plumbing tend to collapse at idle due to the severity of the resistance to flow. Increasing the size of the radiator outlet plumbing to 1-3/4" OD is equivalent to a 62% increase in cross-sectional area. Its a simple and non-controversial improvement. The intention is to bring the parameters under which the Pantera's coolant pump operates closer to the parameters it was designed for.