(moving from the 370 thread) So looking for some thoughts. New to me 1998 370 7.4 MPIs. 310 HP. WOT spec is 4000-4400. Current WOT is 3800 rmp. Assumed it was prop related as they are not the stock 3 blades but 4 blades. Per the SR parts manual, stock pros are 18 x 21 3 blades. So I assumed a previous owner just swapped props -- 18x21 4 blade. Just pulled the nuts off so I could get a look at the markings, I was half right. Current prop is 17 x 21 4 blade (Austral 1721L4Q). So they kept the same pitch but reduced dia 1 inch, assuming to make up for the RPM loss? Reading the interweb, there is conflicting information regarding effect of dia on RPMs -- some say little effect, some say 400-500 rpms per inch. Looks like most owners here replaced their 3 blades with 18 x 19 4 blades (2 inch pitch reduction). My understanding is the 2 inch pitch reduction will offset the RPM reduction caused by the 4th blade. So is my best bet just to add some 18 x 19s and enjoy? Thanks in advance.