New water pump 6 impellers whats up with that!

The depth of the cavity behind the impeller is not important in this case. that is the intake side, and with that open impeller design you can't pull much head anyway.

What is more important is the clearance between the blades & the cast housing. The closer they fit the better. This allows it to produce pressure at the tip.

The next trouble spot is the open design of the impeller. to work well it needs to sit close to the surface behind it in the timing chain cover. Again, the closer it fits, the more effective it is at pumping.

Those two things you have some control over. The final thing that determines pump performance is the ratio between the outside diameter of the impeller, and the diameter of the intake bowl.

Do you have a picture of the dreaded 6 blade pump to compare?

Before you install that pump, measure the clearance between the blades & the pump casting.

Then measure the hang out from the gasket face to the back surface of the impeller.

Then measure the depth of the impeller cavity in the timing cover from the gasket surface. Or use a bit of modeling clay, and trial fit the pump with no gasket.

whatever method of measurement, what is the net clearance of the impeller?

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