Always a tough one to call. Old school rules on props usually say that going pitch to pitch like for like from ally to stainless will always drop your rpm a fair bit and gain some speed top end.
this can be true...but on the odd occasion, you can find that the stainless prop (especially if it’s a good one) can give you that much hull lift over the ally prop, that there is less resistance and drag to push through the water...then what can happen is the engine can occasionaly gain rpm over an ally prop. Of course gaining pace too.
mall depends on the prop really. The black max ally prop is an outstanding prop to be fair. Certainly in terms of ally props in general.
Id never be so bold as to assure anyone how a prop will perform on a boat and set up I don’t actually know or have seen or been on in person...but I do know that in most cases, mirage plus props and their often 1” more diameter over the usual of the same pitch...can be a handful to swing well or to best effect.
Id hazard a guess, that in your situation, you’d most likely drop rpm with the change over. But you have rpm to play with, given your current situation. Long story short...diameter can make a difference. No doubt about it. Especially going from ally same pitch to big stainless same pitch, but an inch more diameter. If your hull doesn’t take to the mirage plus, it may drop 200rpm or close...but if she does take to it...who knows. She could see the same rpm, but noticeable top end improvements and mid range cruising certainly.
So many Variables, it’s almost un fathomable on occasion.
