better hole shot 5.7 mag BIII

[RisqueBznss]

Looking for a better holeshot, esp with a few people aboard. I have an 05 doral monticello cruiser w/ a single 5.7mag BIII. What would be the mods to pursue from cheapest to most expensive?

Thanks!

 

[mcleaves]

Re: better hole shot 5.7 mag BIII

Looking for a better holeshot, esp with a few people aboard. I have an 05 doral monticello cruiser w/ a single 5.7mag BIII. What would be the mods to pursue from cheapest to most expensive?

Thanks!

Props

 

[jerryjerry05]

Re: better hole shot 5.7 mag BIII

You need to post what props you have and what RPM's you are operating at when at WOT.What kind of load etc.
Getting a better hole shot will probably increase your gas consumption and lower your top speed.J

 

[RisqueBznss]

Re: better hole shot 5.7 mag BIII

Thanks, I'll check on my prop size and report back. Does it say the dimensions right on the prop? Or do I need to measure it? How do I measure? Pitch angle and diameter?

Sacrificing top end no problem, it does 45 now and that is more than plenty on Lake Minnetonka. Gas consumption not much of a factor as I don't cruise on plane too much for long. RPM at WOT? I can't remember for sure.

What kind of HP can the BIII handle? I read somewhere 400hp and elsewhere 500hp.

Thanks for your info.

 

[mkast]

Re: better hole shot 5.7 mag BIII

What size boat?

 

[RisqueBznss]

Re: better hole shot 5.7 mag BIII

It is an 05 Doral Monticello, around 26' 6400lb dry, 8'6 beam, power trimtabs

Is there an order of things from least expensive to check?

1. props?
2. engine improvements?

 

[mcleaves]

Re: better hole shot 5.7 mag BIII

A wise old wrench from here (Ok it's Don) once explained to me that these engines are produced by the mfgrs to yield the best possible performance they can. Small tweak here and there are not going to yield much, and will cost a decent sum.

So short of a resolving an existing PROBLEM with the setup, changing props is going to be the faste4st and most cost effective way to go. I run a Volvo DP and have two sets of props. One set gives me a great hole shot but a lower top end. The larger ones are tougher out of the hole but will get me there quicker once up on plane. It's always about compromise

M

 

[TilliamWe]

Re: better hole shot 5.7 mag BIII

Thanks, I'll check on my prop size and report back. Does it say the dimensions right on the prop?

The last 3 digits on the hub of the prop will say either "20P" "22P" "24P" "26P" "28P" or "30P". That is the only thing that matters, as there are no aftermarket props for Bravo 3s. Mercruiser makes them in those 6 pitches only. There is a "cupped" series" of props in those same pitches. There is also a series with a 4 blade forward prop. Propsets new from Mercruiser are $1300.
Here's a link to Mercury's website where you can buy online:

http://www.mercurypartsexpress.com/us/bravo-three-c2101.html

In the meantime, EBay is your best bet for reasonably priced new and used props. And since B3 props don't have rubber hubs, buying them used isn't too much of a crapshoot.

 

[TilliamWe]

Re: better hole shot 5.7 mag BIII

What kind of HP can the BIII handle? I read somewhere 400hp and elsewhere 500hp.

Mercruiser puts the Bravo 3 behind the 496MAG (375hp). They put the Bravo 3X behind the 496MAG HO (425hp), and they put the Bravo 3XR behind the HP525EFI.

Here's that link:

http://www.mercurymarine.com/engines/inboards/sterndrives/bravothree.php

 

[RisqueBznss]

Re: better hole shot 5.7 mag BIII

Thanks Mccleaves and Tilliam! Very informative. I'll check to see what I have and post back.

What kind of improvement can a change in prop setups make? I know it depends on what I already have but I'm not sure of the range here. Is it 10%? 20%? less?, more?

Mccleaves, yep, I understand that lots of R&D goes into these things. Just trying to gain a bit from experts here of any worthwhile improvements. I saw there are supercharger options at around $5,000 but that is a lot of money. Did see a variable vane turbo (aerocharger) for $2500 that has been applied in marine conditions and the design supposedly mitigates heat problems.

But I like starting at the cheapest solutions first then moving down the list.

Thanks!

 

[TilliamWe]

Re: better hole shot 5.7 mag BIII

Without knowing what your current WOT RPM, Top Speed (GPS confirmed), drive gear ratio, and prop pitch, it's impossible to tell you if you would get any improvement at all.

 

[Dave1251]

Re: better hole shot 5.7 mag BIII

You have a classic case of an underpowered boat. The 5.7 will never have the torque needed to make the boat plain quickly. Adding speed equipment will not help hole shot and could even make it worse.

You can make the most of what you have by changing props for hole shot at the expense of top speed. I would try to find a local Merc dealer who will work with you on trying differrent pitches of props on your boat. This will mean that you will have to pay full retail for this service, but it's better than making a $1,300.00 by buying the wrong size on-line.

 

[TilliamWe]

Re: better hole shot 5.7 mag BIII

making a $1,300.00 by buying the wrong size on-line.

Again, once we know what his WOT rpms are, it'll be very easy to recommend a prop pitch. And on Ebay, B3 propsets go for under $500 all the time.

I agree, 300hp 350 is not a ton of power for a 26' cruiser. But, it's not underpowered. My dad's 27' Chaparral Signature (similiar weight with a 9' beam) had a 350MAG MPI, and with a 2.0 to 1 drive and 22p props, it planed quickly and still ran about 42mph top end. And got 2.2mpg when cruising.

 

[RisqueBznss]

Re: better hole shot 5.7 mag BIII

Saw boattest has the 5.7 MPI 300hp 4800-5200 rpm WOT.

 

[Bondo]

Re: better hole shot 5.7 mag BIII

Ayuh,...
With small enough props, That driveline will turn 5200rpms pushing the Queen Mary....
It'll still be Underpowered though...

 

[45Auto]

Re: better hole shot 5.7 mag BIII

Saw boattest has the 5.7 MPI 300hp 4800-5200 rpm WOT

We need to know the WOT RPM your boat is giving you in real life. It's SUPPOSED to be 4800-5200 RPM. Your's may or may not be attaining that recommended max RPM. Your real life WOT RPM is what will determine any prop recommendations.

 

[RisqueBznss]

Re: better hole shot 5.7 mag BIII

Thanks for the info. Guess this will be a spring project as it's already out of the water and i don't know the WOT RPM exactly.

 

[bkwapisz]

Re: better hole shot 5.7 mag BIII

I'm not sure if it helps but my 99 SeaRay 280SS has twin 350Mags with Bravo II's and the MAX WOT RPM is 4800 at best once on plane with the drives trimmed optimally and going full out with empty holding tank, full water (30 gals), full fuel (128 gallons) and just me (275#). This equates to about 47MPH via analog and GPS together. I can't get any more out of the engines without picking up the drives more and I am afraid to get cavitation and have them flare.

Can't tell you the pitch of the props, but they're stock. I have to trim the drives all the way down to get up and then adjust them back up to level. Also have to just about floor it out of the hole but once I got the jist of it it leaps up on plane nicely for a heavy boat, even loaded. If I don't lower the drives to launch it takes forever.

 

[Texasmark]

Re: better hole shot 5.7 mag BIII

My humble opinion. All things being equal, if all you want is a better hole shot and don't want to mess up any other things you have that you like...................vent the prop you have. BTDT

Venting is the placement of one hole per blade just above the blade at the front of the prop. Most HP SS props mfgr'd today are vented.

The holes introduce engine exhaust across the blade at low rpm's. This significantly reduces the density of the medium in which the prop turns, reducing resistance. This reduction of resistance is like doubling the hp of your engine or halving the weight of your boat.

The rpm's come up fast allowing your engine to develop it's hp faster. As mphs increase, the proportion of bubbles to water dimishes until you get to a point (was 35 mph for me) where the water flowing by the prop hub seals off the holes. At that point all your blades see/feel is water and the boat takes off just like the holes weren't there.

If your current prop doesn't have them, a qualified prop shop can drill out some for you. If your prop already has them then you will have to do other things that will affect other things you may not want to change.

HTH

Mark

 

[TilliamWe]

Re: better hole shot 5.7 mag BIII

Mark, venting Bravo 3 propsets (there are two props involved here) is not a good idea. Mercruiser doesn't do it for a reason.