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Old 06-14-2018, 11:50 AM   #1
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Default 2400 scr prop thoughts

I’m a new owner to my 96 2400 scr, the other weekend I had the wife and in laws on the boat. When I tryed to get on plain oh my lord a few times I didn’t think it would happen lol.
It’s a 5.7L with alpha one - 3 blade 17 pitch prop aluminum.
Now the manual says I should be wot 4900rpms at 45 mph.
But only reached 36-38mph and 4100 rpms.
I was looking into 4 blade props, one marina recommended 18 pitch 4 blade, the other marina said that will make it worse and go to a 15 pitch 4 blade.
On another forum a guy said he tryed the 15 pitch 4 blade but he ended up blowing up the alpha or somthing along those lines. Anybody have any opinions on this? Is it even worth changing to a 4 prop or should I just leave it.... or try a 16 pitch 4 prop. Ahhhh I’m a rook and really not sure LOL
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Old 06-14-2018, 01:45 PM   #2
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All Mercruiser inboard (including IO) engines have a max RPM range of 4400 - 4800.

Max cruise speed is a bit of a pipe dream unless you have 1-2 people, half fuel, no water and no gear in flat conditions. It's more about marketing than reality.

17" pitch is pretty low.

I'm going to guess that you had everyone sitting in the back in the solon, and possibly had coolers as well.

First off, go out with you and one other person to get a baseline. Try to reduce as much gear as possible. half-fuel, half or no water. no coolers. Get up to the max rpm of the boat. It should be between 4400 - 4800. If it is over 4800 you need to increase pitch. If it is under 4400 you would need to decrease pitch (I seriously doubt you need to decrease pitch).

Adding a blad would be the same effect as increasing pitch.

You more than likely need to shift weight in order to get on plane. I used to store my coolers, honda generator, and dinghy all down below and as far forward as I could. If I had people on board, they needed to move as far forward (not out on deck) as I could get them in order to get on plane. Once on plane, people can move around as needed.
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Old 06-14-2018, 04:22 PM   #3
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What shrew said.
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Old 06-14-2018, 05:07 PM   #4
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Good Morning.
I have a 1995 2400 SCR and at present I am running a 14.5 Dia X 19P with just the Wife and myself With light load 1/2 fuel, 1/2 water and a small ice chest I can only get to 3800 rpms and about 35 mph. And that is on a glass smooth lake.
I would not imho put any prop with more pitch than a 17.
And to answer averyones question I have a 14.5X17p in a box just have not had time to put it on.
Don
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Old 06-14-2018, 05:34 PM   #5
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Quote:
Originally Posted by donald View Post
Good Morning.
I have a 1995 2400 SCR and at present I am running a 14.5 Dia X 19P with just the Wife and myself With light load 1/2 fuel, 1/2 water and a small ice chest I can only get to 3800 rpms and about 35 mph. And that is on a glass smooth lake.
I would not imho put any prop with more pitch than a 17.
And to answer averyones question I have a 14.5X17p in a box just have not had time to put it on.
Don
You have to get your RPM up over 4500-4800. I don't know if the 17P. would do that. The 17P. is 14.5 to?
Normally you should be able to get up there with what you have now, but you may need repower the engine.
I suggest a compression test.
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Old 06-15-2018, 04:28 AM   #6
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The boat came new with a 14.5X17p from the factory. I have the original documentation that came with the boat. even though I am not the original owner.
The max RPMs for that engine is 4200 to 4600 RPMs. The 5.7 Mag runs higher RPMs, and a 1995 was not offered with a 5.7 mag engine Alpha 1 Gen 2.
Don
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1995 Maxum 2400 SCR 5.7 A1 G2 LUNA DE MIEL
1988 Bayliner 2455 5.0 IO (sold)
1987 Seaswerl 18ft C. Cabin 4.3 IO(lost in fire)
1976 16ft. Tahiti 2.5 IO (sold)
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Old 10-09-2018, 02:22 AM   #7
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I just ran across this thread (after 4 months) but wanted to post my story on the prop/rpm discussion.
I purchased my 96 2400SCR with 14 hours on it. It's 5.7L with 2 barrel carb and Alpha 1 gen2 drive. It came with a 17pitch prop. It would hardly get on plane with 2 persons and 3/4 tank of gas! Long story.... I ended up with a 15 pitch prop which got my rpm's up to around 4200. I asked around and everyone said 17 to 19 pitch was spec.
Not on my boat! Later, I purchased an aftermarket out drive and had exactly the same rpm. I thought maybe the drive ratio was mis-marked.
Gave up and just run with the 15 pitch. Never figured it out
Nick
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