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Old 04-17-2012, 01:28 PM   #1
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Default A: "What prop is best for my boat" again :) 2300 SR 5.7 efi

As the topic title suggests,

I'm having a hard time to choose a prop for our boat. It's a Maxum 2300 SR, 1998, with a 5.7 EFI mercruiser and alpha one drive. I don't know what ratio this drive is, or how to find it? If i'm correct this is a 250hp engine.

Currently we're using a high 5 prop, but i'm not to pleased with pick up nor top speed. (37 mph with 3 people onboard, half tank of gas.)

I've been reading sooooo much about props, i simply don't know what to do anymore :s

Who has real hands on experience and performance figures for this boat? And perhaps some other ways to increase performance for this engine? Any input is greatly appreciated.
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Old 04-17-2012, 02:09 PM   #2
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Max RPM for that model is 4800 to 5200. What are your average RPM's at WOT? What are you referring to when you say 'Pickup"? Is this getting out of the hole and up on plane from a dead stop? You should remain within your MAx RPM range. That being said, you are going to trade hole shot for top speed. Better hole shot, lower top speed. Higher Top Speed and slower hole shot. Everything in between is a compromise.
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Old 04-17-2012, 02:34 PM   #3
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Hi, with pick up i indeed mean starting from dead stop or walking speed.

Out of the top of my head, max rpm was at 4800rpm, but could also have been 4700 bit in doubt there. The boat will be put in the water again in about 2-3 weeks so than i can test again to be sure. I'm supposed to get a call later this afternoon of the people where the boat is in the winter for the details of the current prop.

edit:
And i thought for this engine the rpm's were 4400-4800? Thats what i get when i search the web

Edit2:
Just got a call back from the people who service the boat, it currently has a 13.25x19 high 5 prop fitted.
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Old 04-17-2012, 03:40 PM   #4
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welcome to the zoo....the standard carbed engine is between 4400-4800 rpm wot...the efi or mpi engines are 4800-5200 rpm depending on where the rev limiter is set.....so if your running the efi engine...you should hit wot at about 5200rpm.....anything under that ..your over propped....anything over that your under propped.....nobody can give you exact numbers cuz you need to go by what is wot....do you have trim tabs.....use them to help get out of the hole...do you run with the drives all the way down out of the hole and then bump the drive up as you get out of the hole??..that can affect the performance too..

a few other things to think about....is the hull clean..???...engine in tune....gas fairly fresh....??...all of these factors can affect the boat's performance...

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Old 04-17-2012, 03:50 PM   #5
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Ok, i will look into the rpm's when the boat is back in the water. Boat/hull were clean, gas fresh. The hull is cleaned every year and antifouled.

Usually from dead start either the trim is at it's lowest or a tad above the lowest position, once the boat is on plane it's trimmed up to get it more out of the water. The boat does not have trim tabs installed.
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Old 04-17-2012, 05:53 PM   #6
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If this is a 5.7 TBI EFI it is 4400-4800 WOT

See attached
Mercruiser Service Manual _17 page 1B-8.pdf

Mercury has a really good Prop selector tool on their website

http://www.mercurymarine.com/propellers/prop-selector/
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Old 04-17-2012, 08:13 PM   #7
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Yes, it's a Thunderbolt V EFI.
I've walked through the prop selector a couple of times, unfortunately it doesn't have the info on our boat I've tried to enter as much as i know and then it gives about 8 possible props. (un)fortunately, not the one we have.. So improvements should be possible

Does anyone have any performance figures with different props?

Furthermore, is this the engine on which it's possible to gain about 20-30hp with different exhaust manifolds? Sounds a bit to good to be true to me But i was looking at the IMCO marine Thumper Power exhaust kit, http://www.imcomarine.com/cal_store/...kit-black.html or the http://www.imcomarine.com/cal_store/...m-mercury.html

Will these give a noticeable increase in performance, and also finally release some of the V8-gurgle? Now it almost sounds as a sowing machine... My 4 cilinder 3.0 mercruiser sounded more dangerous lol
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Old 04-18-2012, 07:36 PM   #8
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I found a number of links that also state max RPM is 4400-4800. I'll recant my previous statement. You're already at the top of your max rpm range, so you're not going to be able to do much for hoel shot. Increasing pitch will increase top speed but decreawse holeshot. Does this boat have trim tabs? Are you working the outdrive trim as well. Trim tabs would help get on plane faster as well. Almost 40mph with that boat is not bad. You could probably eek a bit more out of it. How many seconds to get on plane?

I don't think performance exhaust is the way to go. No offense, but this simply doesn't sound like the boat for you. A cuddy is not really a performance boat.
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Old 04-18-2012, 08:20 PM   #9
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Cuddy?? It's a bowrider (SC is cuddy, we've got an SR)

Personally i don't think i'd have picked this boat... But it's my dads and now basically me and my brother have got it at our house. He uses it about 1 or 2 times a year. And well, we just would like a little bit more 'oomph'


It's without trimtabs. Once we've picked it up from the winter housing i'll do some tests on how many seconds it takes to get on plane and what rpm's it really does at WOT. I always use the trim depending on what we're doing.
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Old 04-18-2012, 09:03 PM   #10
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Based on the performance of my 2400 SC3, which has 50 more HP, a B3 drive, but is a little heavier, your boat ought to do mid 40's for MPH and get on plane in probably 5-6 seconds with a light load. Try to find out what the original prop specifications were and work from there.
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