1st version - plastic impeller, shattered from fatigue. 2nd version - sheet metal impeller, 3rd version - composite (brown color) impeller. Composite is still OE today and was the final fix. Composite is also about 0.5lb lighter than the sheet (and cast) metal which helps extend the bearing life.
Mainly using my eyes to test flow, lol. Cast impeller has rough, smaller sized ports. Unless you are running an overdrive pulley the pump isn't spinning any faster so how could it have the same flow as an OE pump?
I don't understand the immediate thinking that metal MUST be better. Yes, they screwed up on the plastic one but BMW also never made an OE cast version.
You'd probably have to post-machine the casting to get even and smooth ports. It was easier to do the sheet metal as a quick solid fix when all the plastics were exploding. Then back to a lighter, more durable, and most likely less expensive composite version. __________________ ~Dave~
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