With a 4.3L, you would have a 1.84:1 ratio drive depending on the year of drive, if in fact it is original etc.,etc.,etc. (the new ratio for replacement drives for your boat is now a 1.81:1 if you ever have to replace) Anyway, back to your question about propping: If you are underpropped and are running over the WOT at say 5200 you will probably be down to around 4800rpm (If everything is the same as when you attained 5200 with respect to weight of fuel, # of people on board,gear etc.,etc Usually, I believe that you loss around 400 rpm for every increase in prop pitch. I am assuming that you have a 14 and 3/4 x21 pitch aluminum three blade prop and if indeed that is the case, you may be able to step up to a 14 3/4x23 pitch aluminum three blade. Prop pitch is based on power to weight ratio but other factors can come into play. (waterlogged hull,growth on bottom of boat, engine performance and probably a few others that I can't think of at the moment). It is basically a learning curve when it comes down to propping through trial and error but just the same you want to be close off the bat instead of being way off in the beginning and buying several props to find out. (like I did)lol But don't forget all has to be the same as when you tested and reached 5200rpms. Also, the engine should be able to reach WOT with the higher pitched prop or it will overload your engine system and shorten life of motor. You only should reach WOT for short periods of time just to make sure engine,drive,prop etc. are able to achieve that goal. I wouldn't be running that engine at 4800rpm let alone 5200 too long or often for fear of overheating or even worse (blowing engine to pieces). Better make sure you got your eyes fixed to the gauges when your doing so! jmho. Again, you are supposed to occasionally reach WOT just to see if engine is operating properly but only for short periods of time. (look at your manual) You will notice that the boat with the higher pitched prop will take a little longer to get up on plain or out of the hole but you will see a little increase in top end speed. If you are doing this simply to lower the over-revving situation I would definitely say do so! If you are doing it to gain more speed I would say forget it! I went through 4 prop changes with a 1:84, 180 horse four cylinder engine and this is what happened: Original well worn 14x 19 pitch,3 blade aluminum over-revved at about the same as yours. Reached top speed of about 32-35 miles per hour. Installed a 4 blade aluminum 14x20 pitch prop and did not gain much if any speed and dropped rpms around 400. (maybe 35-36mph) Tried a 14x21pitch,3 blade and reached about 38 mph at about 4600 rpm. Just installed a 15x19 pitch three blade alum. prop and seems to be doing the best so far at around 35mph at 4200 rpm (my WOT is between 4200-4600) so I am at the bottom end on that but I think it will be ok. Just trying to give you a feel before you go and spend. It may take you more than one try to achieve what you are trying to do. Just sayin, that's all. Every boat is a little different. I just don't know how that loss of 3/4 diameter will help you much. Maybe stay the same with diameter (14 3/4) and go to 23pitch theoretically dropping 400rpm and gaining 2-3 mph.jmho. Worth a try, right? P.S. What year 4.3L and how much horsepower you got? I think some of the newer 4.3's put out up to around 230hp but I think the older 4.3's put out around 180 or 190 hp so there is quite a difference in power if you know what I mean. best of luck, Tom
