There are two basic 'styles' of water pumps for the redblocks: closed impeller, and open impeller

This pic is of three B230 water pumps:

...on the left is a Volvo pump [a used one], showing it's use of the closed impeller

...in the middle is a Hepu brand water pump, also showing it's use of the closed impeller

...on the right is an aftermarket [unknown origin] water pump, showing it's use of the open impeller.

The closed impeller flows better than does an open impeller, with less cavitation.

I have used Volvo and Hepu water pumps for years. Both are of good quality, and perform well and are durable.

I try to stay away from open impeller pumps. They do not flow as well; and I have had a few problems with overheating during hot summers on motors that had open impeller pumps. Just changing over to a closed impeller pump corrected the problem.

and yes, those three pumps are sitting on a freshened 1992 B230F shortblock.....knurled pistons, new rings, and bearings. Just about ready for install. It will be getting the Hepu pump.