S4Hadi

The boat is a '98 Formula 252LS 7.4MPI/310 bravoIII 2.0 with 28P's and at WOT pulled 4200-4300rpm's at an indicated 56-56mph.

The Formula dealer guide book lists the boat with 26P's at 53-56mph at 4800rpm's and it lists the optional 502MPI with the 28P's. So I concluded that I'm overpropped and ready for a 502MPI transplant... which I did this past winter.

It's all good, she starts, idles, run strong right to the 5000rpm recommended WOT at an indicated 65mph+ (speedo 65 max), wow, what a difference 105HP's made! That was with 2 people and about 85 gallons of fuel onboard.

My questions now is if I'm underpropped? The boat pulls stongly right to 5000rpm's and it feels like it wants to go beyond and there still is some throttle left at that speed.

Is it OK to go beyond 5000rpm's and see if she goes to when the rev limiter kicks in?

Mercruiser literature lists with 502 with a bravoIII with a 1.5 reduction vs my 2.0 that came with the 7.4MPI.

Should I look into changing gear ratios or maybe 30P's... or just have my 28P's re-pitched?

It's all good, mon

Jamal

Mbam

Sounds like you go a good result.

Re-pitching more than 1 inch is not possible. Yuo can see if it will actually hit the rev limniter, but do not hold it there. The Brsavo III props come in both a cupped and uncupeed version, do you know which one you have? Changin to the cupped veriosn will drop you about 200 RPM.

The dirrefanc betwee 2.0 and 1.5 drive ratio would reperesnt a 33% change in pitch, that is 34" form the 26's yuo mention, so something is wrong with this info.

S4Hadi

Marc,

Are you implying that my 2.0 reduction is correct for my application?

I do not have a Formula dealer near by, but I have looked at some Cobolts and Chapparels with the duo props and the all have the 2.0 ratio with 26P's on them.

How can one check to see if my props a of the cupped variety? The part numbers are : 48-823670 and 48-823669. How much difference in rpm's would re-pitching do... abviously it is less costly to do that than to purchase 2 new props.

Any input is appreciated,

Thanks

Jamal

Nordicflame

The next step up in gearing for your B3 would be 1.81:1 and not 1.5:1. I went from 1.81:1 to 2:1 and from 26's to 28's and the boat was much more responsive. Keep your 2:1 ratio and send your 28's to Bronson Hill. They will take 200-300 rpm out of your props and gain you a little speed if your hitting the rev limiter. Merc also makes 30's if this were not enough.

S4Hadi

Thanks for the input. At what RPM's should the rev limiter kick in on the 502MAG? What is involved with the changing of the drive ratio?

I was thinking to maybe wait with the re-pitching the props until I do some more mods to the motor... it's so tempting. I'll do some more testing like how a couple more passenger affect the WOT rpm's.

Jamal

RickA

Jamal

I just finished a repower with a 502 Mag in my 22ft Crownline. I also changed gears in my Bravo 3 from 2.20 to 1.81 and 26 pitch props.

I've only had the boat out twice and the results are as follows...68 mph (GPS) @ 5050 RPM which is right on the stock Merc rev limiter.

Crownlines are far from a performance boat with their hooked hulls, but 68mph (GPS) is not too shabby.

S4Hadi

Very interesting, my friend has a 22.5ft Crownline that he special ordered with a 502MAG... his dealer special ordered 30P's for his boat. Not sure what the drive ratio is... this duo prop bravoIII certainly performs well, he can peg his speedo (indicated) all the way.

Anyone out there than can explain the duo prop/drive ratio relationship. How come there seems to be no mention of the pitch, only the diameter when people refer to the duo props?