Prop Guidance
 

Ok guys time to turn to the boat gods and get some opinions. I've finished the upgrades on my 1989 Formula 272 SR1. Motors are running drives are installed going to be time to hit the water soon. boat was pretty stock a few years back when I bought it. Was a stock 454 330hp twin screw. The bravo drives had standard mirage 25p 3 blade props. Now I know these boats are heavy and built to handle the rough stuff. I know I'm going to need to go up in prop size. Ive installed stroked 489's at 525hp per side. So a bit of a upgrade. Im trying to decide prop size on this old heavy bird. Im also looking for suggestions on the prop to go with. I was thinking about going with a set of 29p hydro-motive four blade cleaver style, but some said they might not work well on a heavier boat like mine. some have suggested going with a Bravo or a mirage plus. I think id rather go with a Bravo prop between those two but I want to know your thoughts on this. any idea where I should also start with size? I was thinking around a 28 or 30 pitch would be a place to start, but the prop game is something I will admit that I know nothing about.

I am assuming you will be running the new engines at a higher RPM then the original. Run the old 25 inch mirage props and see what happens. Record the data and post it. You really need a base line to get an idea what is needed.

Padraig

No way you will be able spin 29 Hydro's with enough rpms. Like was said, try your 25's and then go from there. You'll prob want to spin the 489's to about 5400 rpms.

That was my next question. What is a safe rpm to shoot for?

I will echo what the others have said. Too many people upgrade HP and immediately jump into unknown prop land. Use the original props, get the motors sorted out in the boat, log some good prop data (rpm, GPS speed in increments of 250 rpm from idle to WOT). THEN post the data and we can see where you might want to go.

If you go from a 25" 3 blade to a 29" 4 blade you will bring the motor to it's knees.....The rpm you need to target should be based on the internal parts, and cam/head selection where peak HP is attained. 5400 rpm as Griff suggested would be where I would start.

As others have suggested, what is the max RPM/redline on those motors and what RPM's produce the max torque and or horsepower? I would also do as others of suggested and get a baseline with your current props... GPS mph vs. RPMs.
I am still just learning but I would target a prop that let your motor spin up to about 95% of its redline.

Do you have dyno sheets??? WOT rpm really depends on internals. If your build is pretty typical with decent parts and it makes a true 525hp, its probably making that HP in the 5400-5600rpm range.

I don’t have any dyno time but here’s the list of parts on motors.

Mark 4 489
eagle rods
eagle cranks
srp Pistons
088 heads
inconel valves
Insky springs
crane gold rockers
Comp roller cams
mellings pumps
9.7/1 Comp
4/7 firing order

To echo what Griff said...the dyno sheets for my built 496's have been lost but I have been told 5,600 max rpm.

Are they carbed or EFI and whats the specs, whats the spec's on the cam,

Holley 850 carbs.
I don’t have dyno sheets. I’m going off of what I was told. Bought these motors after they were put together. They were pulled out of a cig.

Very hard to beat the 4 blade Bravo One props for all around.
Like others said. log your originals first.

I've got twin 502MPI on a 32ft Sutphen. About 450hp but stock cam, just exhaust and much higher timing than stock. Run premium fuel though.
Run 79 with 28P bravo at 5050, fairly light load.
Run 76 with 26P bravo at 5250(my motors are out of hp by then)

Lihe he said below, 25/3 to a 26/4 blade is a jump already. Dont go buy any 28's just yet.
good luck.

So I actually got in contact with the original builder of these motors. And from what he was saying these seem like pretty healthy done motors. Came out of a flat deck cig from Ohio. Ray said he’s going to find me any or all the paperwork he has on them. He said the cam’s power band is at 5800 rpm. He said no dyno time on them as he never did it. But he said they don’t have more then 50 hours on the rebuilds. And that it pushed his gun to gps run of 70mph. Now I just gotta work On getting this trailer back together with new brakes and bearings and shove it in the lake and see what I can do with it.

My 292SR1 with built up 454MAGs spun 26P Bravo 1 props a little north of 5k RPM. I always wanted to try 28P but never got around to it. The box stock 26P Four blade wheels worked great all around for me.

Yea I for sure want to get rid of these three blades and would really like to go to a bravo 4 blade.

4 will always be slower than 3's...........someone on fb was selling some 28's

Is fours something I shouldnt be considering? I dont care about that 1 0r 2 mph. (atleast not yet) I want something that handles good and is overall a smart move. I dont want to get ahead of myself but at the same time I dont want to be behind on things either. Before I make a solid decision I want valuable information to make that decision. Thats why I turned here, I know there is a wealth of knowledge.

Id prop for out of the hole and cruise.........I had 28 4b on a 38 TG with 500 efi's and they worked well

Smoke eater,

I've always had good luck with the Bravo 1 four blades on my Formula's, the 357SR1 I have now has a set of 3 blades on it and I plan to try out 4 blades in the future. The 4B seems to get out of the hole effortlessly and provide me with a solid cruise characteristics. TomZ piloted my last 292SR1 a few years back and may have some input on how the ride was. We are rarely lightly loaded since we typically have friends, kids, and gear aboard so we were always propped for midrange performance. The 292SR1 was into the low 70s with 4B props.

Awesome Thats how I will be as far as being a heavy load with gear fuel and family. I just wanted to make sure I wasnt going to make a mistake by going with a 4Blade.

The 4-blade will be good on the 272... it really worked well on the 292 and being that they're pretty much the same hull, I think they'll do just as good. However, I would go ahead and run what you have now for a baseline. The 25P Mirage may be a pretty decent in terms of getting into the proper WOT range. What do the engines have for cams?