Re: new prop help
OK, with more info I think I am now beginning to see nuggets what your problem may be...
You are very much underpropped. However your initial comment that it is difficult for you to get on plane really throws me off. Boats that are underpropped are VERY fast and easy to get on plane, but their engines over-rev and they have low top speeds.
And now you've made an elevation comment, which opens up a whole extra can of worms as well and we need to know yet more data: What altitude are you at, and what altitude do you plan to normally use this boat at? FWIW, taking this boat to a lower altitude will make it REALLY rev up high if it is revving too high now...
You are correct in fearing going much past 5,000 rpm. Don't do it.
You indeed have a 1998 5.0L 220 HP 2bbl Vortec motor, rated for 4,400 to 4,800.
1.81 sounds to me like a rather low drive ratio for that motor in that boat. And an 18 pitch is a rather low pitch for that motor. As a combo it sounds as though it is geared and propped very low overall. There is a good chance this is because it was set up to run at very high altitudes where it is choked for air and therefore making much less HP? Maybe because it is a "frankenboat" that has had outdrive repaced by someone who didn't really know what he was doing and put on the wrong ratio? I have no idea....
Is there any way you can get a larger pitched prop to borrow, and try to run it and see if your RPMS stay at or below 5,000? Maybe a 21 or 23 prop....especially if you're going to run it at lower altitudes....
We really do need a full speed, WOT run, and all the data from it, from a known prop, to get a good snapshot of how to properly prop this boat. But do NOT risk spinning it past about 5,200 to 5,300 RPM for any length of time. A short run at those speeds to collect data is OK, but no faster than that...I don't want you to damage anything. If such engine speed happens, you need to back out of it, get a larger pitch prop, and try again.
Keep in mind also, if this boat is set at altitude the carb may have been rejetted for the same. If so, it will have smaller jets installed. When you had it apart to rebuild the carb, did you note the jet size? Because if you run the smaller high altitude jets at low altitude, you will run the risk of running the motor too lean...which also may not be a good thing and could damage the motor. I suggest you check the jetting of this carburator with factory specs if you think it may be set up for altitude...before running it at lower elevations.
