On Thunderbirds there is a open spacer between the water pump and front cover - moves the pump forward toward the radiator about an inch or so. The spacer creates a huge space behind the impeller - makes it spin in a large very open cavity. Destroys any hope of pump efficiency - in my opinion. There is available a stainless baffle that sandwiches between the impeller and the open cavity to try and cut down on the volume of the swept space. Seems a reasonable idea.....
Accounts vary on whether it works or not. CASCO (t-bird parts supplier) has run a test you can find on their site - and the test shows the baffle failed to solve any problems. They got better results by (1) using a free(er) flowing thermostat and further (2) by using a modified pump impeller that sweeps more of the opening in the spacer.
Baffle didn't do anything for my outfit at all - waste of labor and gaskets. By comparison, the larger flow volume thermostat showed a change for the better on my infrared temp gun right away. It also helped instantly to put an orfice in the bypass tube between the manifold outlet and the pump. Cuts down on a huge "short circuit" that allows for quick warm-ups - but then never ceases to re-circulate the max temp hot water.
Steve Metzger Tucson, Arizona