RPM to prop for vs dyno chart.
 

I just pulled my motor off the dyno. It made 572hp @5600 when cool. After multiple pulls it made 551@5600
I am using the hot pulls to go off of.

3500-383hp
3600-395
3700-405
3800-417
3900-425
4000-427
4100-436
4200-444
4300-450
4400-458
4500-467
4600-478
4700-484
4800-490
4900-503
5000-512
5100-525
5200-538
5300-544
5400-546
5500-550
5600-551

Last year with a tired 420hp, I could spin a 23 mirage to 5000rpm. This year I was thinking either a 25 or 27 mirage plus and propping it for 5300rpm. What do you guys think my target WOT rpm should be? And what prop would get me there?

I'm curious what all did you do to your engine to go from 420 to 572 hp?

Slightly better heads, bigger cam and a supercharger.

You might be surprised, but your 23 might be the prop.
5700-5800RPM light load, opinions might vary.

I would prop to your peak HP which appears to be around 5600. Otherwise you are leaving performance on the table.

As a baseline I would start in water testing with your existing prop. Yes you may be under propped but you also haven't spun that prop past 5000 rpm either. Once you get a feel for how your boat and prop perform when north of 5000 rpm you can start with prop selection. If you need more prop then work up the pitch ladder.

trial and error. You'll prolly end up with the 25 if I had to guess but like rookie said you may end up with same prop and spin it a little more. Gotta tune it for what it likes including boat characteristics, handling etc. I can give u an example from back in the day with a twin engine 28 I had. Started out with a pair a toad 330's and then built some others with your basic 454 upgrades including worked dart heads, intakes, carbs, comp etc. ended up with 480 hp. So close to yours in regards to gains in power. 150 + -.

Boat ran came new with 23 mirage that ran 46-4700 with the 330's and ended up going with 25's that ran a conservative 5,600 with the new builds.

Will give you some kind of an idea. What were your torque numbers. Also curious what cam you swapped out to cause if I'm not mistaking the 420hp cam is the same one merc used in their 525 sc's. You running 250's or tuned 177's.

Personally I've never had any luck running bbc's much under 5,400/5,500. Anything much less than that just feels lazy.

577 torque at 3600rpm. I went from the 132561 "420" cam to a crane 134561. It made over 550lbs almost everywhere. Torque monster.

I am running a 177 525sc setup. I am running that 134561 cam and 9:1 compression. So I am a little hotter that the standard issue 525sc.

I think I'd try the 25 Mirage plus...

25 Mirage Plus, and prop for 5500-5600 rpms with a normal load of fuel and folks. You would probably need to have the 25 labbed to get your rpms high enough.

Personally I would go with a four blade like a 24 Bravo or maybe a 23 Rev4. My rig, though bigger, runs the exact same speed as Mirage Plusses with Rev4s and handles much better. I found the same results when I tested props on my 22 Whaler, the Rev4 ran just as fast as the three blades.

The more I think about it the more I think the 23 Rev4 would be perfect for you. I hit 71 at 5300 rpms with decent slip numbers with 23" Rev4s

I have heard that the 242 handles bad with a 4 blade. I'll have to play with it.

I will ask endeavor2 what he ran for prop on his. He had a hopped up worked over 427 in his. Will have him post what prop worked at higher speeds etc,

The guy that put the bbc bravo in my boat, claimed 78mph with 630hp. No idea what props though.

I bought a 25p mirage plus today. I'll let y'all know in a week or so how everything works together.

I was gonna say run the 23 and see what you have before buying anything else. but the 25 is a good middle if the road prop that can always be re-sold...and 2 to compare also will make the first couple of runs more fun.

I'd say to prop it for around 5500 based on the cam. Not sure how much you're overdriving the blower though.
You really don't want to spin the 177 more than about 12000 rpm blower speed. I think max rating is 13500 rpms for the blower, but that really creates some heat.

I am spinning the blower 2:1. So that would be 11000rpm max.

You don't want to lift the stern on a 242 and a 4 blade will do that. I tried a pair of 4 blade 22" on my 255 and it was squirmy once it planed out....the boat wanted to dart around like a top water Bass Lure!! LOL

Sounds like it's going to be fun !! Make sure you have a Kill Switch and Lanyard !! LOL

I haven't had mine out at anything over 50 MPH yet, but the 26P Bravo that I took her out with was great. I have both the 26P and another 28P to try once I get some time on her.

I've heard both sides of the story with regard to the 242... some say 3-blade only, others say 4-blade. Personally, I liked the way the boat handled with the 4-blade. Time will tell.

My boat has a blueprinted bottom with the hooks removed. I wonder if that will effect prop selection.

Might. Hard to say. The hook was only on the outer parts of the hull on our boats. Got to get the boat out of the water.