Is this aftermarket? It's fitted with a 5mm plastic spacer. Would this flow any more coolant with a standard impeller? I think Ben Ballard used to make high flow impellors for sidecar-x I'm wondering if this is one of his covers?
I have a JBS water pump impeller,
It came with a plastic spacer as the impeller is taller.
It was to be used with the std cover.
I ditched the plastic spacer and made a cover.
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The std impeller IIRC has about 2mm clearance to the cover, I reduced the
clearance to around 0.5mm, could be done with the std cover to get better flow as well I think.