I have a Powerquest Spectra 222 XL that had a 330/Bravo 1. With that power I could turn a 21p Mirage plus at 46-4700rpm @ ~57-58mph. Would turn a 23p Mirage plus at 44-4500rpm @ ~58-59mph. I am in the process of replacing it with an old Mercruiser 425 that seems to be in good health. Any idea where to start as far as prop and what kind of mph I should expect? Was thinking of buying a 23p as the one I tested was borrowed, but don’t want to go too small. Thanks in advance.

the 23p mirage plus 3blade seems to be the prop to start with for most boats. Depending on what kind of hp and rpm's you can turn will determine your mph. If you can get that 23 spinning up around 5200rpm you "should be" in the 67-69mph range with all things being equal.

After several projects of getting hyped up about new power, I am sure 99% of people on OSO would say start with your old props first. Assuming the new power can push a few more RPM, you probably will be fine with the 23P.

Sounds good, I’ll start with the 23 and go from there. Thanks for the replies!

The 23 should be near perfect. You want to spin a 425 to 5000-5200rpms.

Okay, now that I think I know where to start with propping I have another question. Do I need a solid hub with 400+hp in a 4000lb 22’ boat with a B1? What is the difference between the old mirage plus that looks like it doesn’t have a removable hub and putting a solid hub kit in a newer mirage plus?

I run the Merc delrin/plastic hubs on my 415hp 502mpi's and have not had any issues. They are not rated for that much HP, but I've never had one go bad.

Hi Griff. Remove the sleeve and check it on the nut end where the aft adapter slies in. Cracks will start to form there first before failure.
I'm sure you keep spares on board as well.
Mercury says over 400 hp should use solid inserts,

Once you have run the 23p, you can input the results into a prop selector..

.https://www.mercurymarine.com/en/us/...or/#!/step-one

Just suggesting you take the prop selector with a grain of salt. When I worked for Mercury service and even more when managing Mercury Racing's propeller Lab, I was asked to help develop the prop selector. I fought that since every identical boat is different. Really, they are all a bit different and people load and use their boats differently.
That being said, the selector can be a starting point but do not take it as the final word. You are better getting base line info with a known true stock propeller and contacting BBLADES or a trusted set up pro to help you achieve your particular goals.

Brett