Are you sure its not 1.32? That was a common ratio for the 454.
The 1.47/1.5 ratio needs a prop with about 2 more inches of pitch to equal the 1.32. So your 19 pitch is like a 1.5:1 with a 21 pitch.

^that was what i was thinking, so if it is in fact a 1.32 or thereabouts and given the rpms he's turning with no trim, that engine must be making some pretty good power.... so, still under propped.

That's quick, mine with the same prop (vengaence 19p) runs only 43mph with the 7,4 330hp merc.
Is the mirage 21p so much better than?

I have a Quicksilver Mirage 48 13702 a41 21p from a boat I had in the 90s totally forgot about it how does this compare to what has been suggested? Thanks

Toss it on and try it. Never hurts. A mirage plus would be a better suit but run what you have and see.

Sure will looks like next year unless we get some warm weather on one of these next few weekends..

I hate that, just got the old bird and have to hibernate it for a few months. Maybe you'll get the weekend you need.

Well this weekend is a wash and I here you when I bought it I new there wasn't much time left in the season but it is still hard.

Her are a few more pictures I also got the little red book with it.

Here is the Alpha 1 drive.