I'll use my best Clinton..... "depends on your definition of efficient."

The star style is the lesser in efficiency of the two you mentioned.
The closed style with the three holes is even more efficient at high
rpm because it doesn't cavitate as badly. The three hole style with the
six vanes were used on the 289hp.

 

Are you sure that's not a backing plate? I know that performance shops sell a pump with a backing plate that improves flow. As I understand it, the backing plate removes the gap between the housing and the impellers.

As far as style goes, I understand the old iron style ones are better than the stamped sheet metal ones. I've heard the sheet metal ones are done because of costs.

Edelbrock makes great HP pumps and probably offer insight here:
Aluminum Water Pumps - Introduction - Edelbrock, LLC.

 

The plated variety for the cavitation reason GT289 mentioned. In fact, adding a screw in plate to the existing impeller is a popular upgrade on Chevy waterpumps to increase efficiency.

 

Thanks for all the answers! I was just wondering because I've seen both on the repro pumps. I might pick up another Flowkooler pump when I rebuild my engine, though I'm kind of hesitant to do so since the old one died in 7 miles...

 

Have you been in touch with the FlowKooler folks ? They've been very reasonable in my dealings with them. I would think they would love to exchange pumps with you, if only to give them the opportunity to examine their failed pump.

Z

 

Good question Kelly.
I have Edelbrock water pumps and like them, when they are cast correctly.
A different story.
Anyway their impeller looks like this.

 

Yep, I've chatted wih them and gotten a full refund. No problemo there. They just had me return it through Summit. Summit is probably getting real used to me returning destroyed parts by now!