Prop starting point
 

Boat is a 22x7 Avanti, basically a standard 24x7 minus 2 feet and a couple hundred pounds. Iy has a small delta pad and the drive doesn't look all that deep either. First run is going to be with a generic stainless 21p three blade. power is a 7.4 nonmag mpi. Im thinking the 21 is going to be on the small side and also thinking of wanting a four blade. Suggestions??

21 should be too small. Used to put 23 Mirage on them with big blocks. They are very stern heavy with the big block. Great riding boat though.