I stopped by Summit today on the way to a job, & picked up a new water pump pulley: http://www.summitracing.com/parts/asp-520141/overview/. This pulley measures at 4.0" diameter as compared to the stock one at 4.5" diameter. I am hoping that the increased water pump speed will aid in cooling when I increase the amount of boost that I am running.

 

Interesting solution. I do recall discussions from long ago when I actually knew a few things that two possibilities can result from increasing impeller speed, one is cavitation and loss of efficiency and impeller erosion , the other is the coolant velocity is increased to the point that it doesn't pickup and remove heat as efficiently as when moving at a slower speed. Guess that's three things.

 

This is the same as the pulley that came from the factory on a 1993 Mustang Cobra. Injected Engineering is running one on a Kenne bell equipped 347 with no issues.