I built one out of a 160 gallon/minute ,2" pump with a 5 hp briggs .................. I used a 2 inch suction and it was strong strong .......... You did not want to let it get ahold of your thigh , lol ................. I am not sure how it would react to a 4 inch suction ,,,,,,,,,,,,,,,,,, it has been a long time ago , I used a simple formula and a little trial and error to get the orfice right to create the vinturi inside the T .................... I do remember I used a 3 inch hose to supply the 2 " pump , just to make sure it had all the water the pump could use................... I took a 2 " iron T and cut it at an angle to take one side of the T off ........ I then took a 2 1/2 inch T an cut it off to fit the 2 " cut T ..... welded the cut off piece of the 2 1/2 to the 2 for a little bigger discharge hole ,,,,,,,,,,,,,,,,,,,,,,,,,, I did not answer your question , but maybe you got an idea of what you need .............. I used it to dredge swimming holes here and found tons of valuables............