I just repowered from a very tired 84 260 hp. I dropped in a 325 hp 357 Mag (300 hp at the prop). I am starting with the original prop I was running last year, a Rev 4 15 pitch. I am positive this is under pitched. Can anyone recommend what I should start with after that? I am thinking a 19P, but either a Mirage Plus or Rev 4? The boat is a Formula 1984 242LS. HELP. I am hoping for 50 mph.

Need more info. What are your current max rpm and GPS speed along with your outdrive gear ratio?

I would start with a 19P Mirage Plus.

Baseline the old prop first.
From there we can all offer ideas and ultimately BBLADES can offer test propellers to do your dialing in.

Let us know how the new power runs!

Brett

It's a 1.55 ratio/alpha. The new engine is rated for 4800-5000 RPM's. Last year I was at 4500/4700 at 38 mph with a 15 Rev 4. The engine was VERY tired and I needed the low pitch to get out of the hole. Hope that helps. Brett....I will call and talk to you when I get an idea when the projects are going to be done on my boat.

Thanks everyone!

I stand corrected 1.47 ration.....

I'd start with a 17 or 19" 3 blade or an 18" 4 blade.

Run the 15" Rev 4 and see how high it revs. If it goes beyond 5200rpms, then try a 17 Rev 4.
I highly doubt you will pick up 12 mph though.