Back to the choice of pumps - the Lotus Elise K2o swap -
he said this about the 200 vs. 400 series pumps, when I suggested that the 200 might be enough for mid engine/K24, referencing the BMW application;
View attachment 63584
Hmm.....
Well, from a coolant flow standpoint the N52 (CWA200 OE application) and N54 (CWA400 application) are almost identical. Extremely similar open deck block, same coolant outlet housing, shared hoses, similar radiator, same thermostat, and so on, except it has two turbos to feed coolant to as well.
I'm not sure how valid that logic is either. Many, many cars cannot run on a dyno continuously and keep themselves cool without absolutely ridiculous fans. At APR/Dinans main facility, for example, they have to have massive centrifugal blowers with intakes 5 feet in diameter in order to move enough air to keep even stock cars cool on the dyno for any period of time. It sounds like the poster above was simply using the radiator cooling fans, and while the CWA400 may be the difference between being able to get away with that and not, that does not mean it's necessary or optimal.
Imagine using
fourty amps (500w) just for your water pump before factoring in the fans, on a measly (lets be honest, in the scope of things) 240hp engine. No wonder it was mentioned as "not being an efficiency/power increase"- that's an issue with the implementation, not the water pump itself.
If you're having to blast coolant through the block and radiator at 100mph in order to keep the engine cool, you have an undersized radiator and are wasting electricity (power) as a coverup. The minimum flow determination should come from little more than making sure your temperature across the engine is not excessive- for maximum efficiency, once that is met (plus a little bit more to help out your radiator), there is no need for more coolant flow. Also, when fitting such a ridiculous pump to a system, you also have to be aware of restrictions on the intake side. With a pump so powerful, it would not be hard to pull enough of a vacuum on the intake side to create significant cavitation- something the CWA will not hold up to.
For reference: the largest pump Davies Craig makes, the EWP150, which is regularly used on Big Block V8s and track cars, flows 60lpm at 6psi pressure differential. Under the same conditions, the CWA200 flows over 120lpm. At flow rates approach 20lpm, the favor begins to shift towards the DC pump, but at flow rates you're more likely to see in the real world, even the little CWA200 blows it out of the water. This isn't to say the EWP150 is bad- it's absolutely not, but just for comparison. It uses 2/3 the power of the CWA200 as well.
Also, those pump curves look...interesting.. but I am not familiar with their specific design traits to know if that looks valid or not.
Even though the safe answer is to just go with the 400 and set the maximum speed to where it begins to cavitate, I seriously do think the 200 would be more than adequate itself. The 400 is just another example of BMWs tendency to go overboard with Factor of Safety on drivetrain components, just like their engines and transmission (selection).