2400 scr prop thoughts - Maxum Boat Owners Club

Kanzzi · 06-14-2018, 12:50 PM

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

shrew · 06-14-2018, 02:45 PM

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.

mmwjr · 06-14-2018, 05:22 PM

What shrew said.

donald · 06-14-2018, 06:07 PM

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

Gugi47 · 06-14-2018, 06:34 PM

Quote:

Originally Posted by donald

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.

donald · 06-15-2018, 05:28 AM

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

NickNick · 10-09-2018, 03:22 AM

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

Calguy · 10-25-2018, 03:08 AM

My 1995 2400 SCR is getting top speed of 47 mph at 5k rpm on 350 Mercruiser Horizon Bravo 2 with a 21 inch prop.

shrew · 10-25-2018, 04:27 PM

That seems unusual. The Horizon is a high-torque inboard engine. I've never seen one married to an outdrive. Its max rpm range is 4200-4800. The 6.2L (350) ECT is a new high rpm engine that has a range of 5000-5400.

What year is the engine?

donald · 10-25-2018, 04:33 PM

Good morning every one.
I finally changed the prop on my 95 2400 to a 14.5x17p, and put it in the water to find that I run at 4400 rpm (not sure tach is accurate) and hit 38mph with gps.
All and all I am happy.
Don

donald · 10-25-2018, 04:42 PM

Calguy
was your 2400 repowered?
I have the original sales booklet and it does not show a Horizon as an option.
The only engines where a 4.3 a1g2,5.7 a1g2 & and a 5.7 bravo 2.
Don

Calguy · 10-27-2018, 10:47 PM

It is a 2008 Mercruiser Horizon 350 FWC and port injected. I installed a Smart Craft Merc Meter read out unit connected to the ECM. Performance is great. The Horizon was sold as both IO and inboard. 4800- 5200 red line. I think it is only sold as inboard now...
Take my word for it...hooked to a Bravo 2....

Calguy · 10-27-2018, 10:57 PM

I was so fed up with my carbureted 350 I did a re power in 2008. Purchased at Doug Russel Marine. The engine was shipped in from the the Sea Ray plant as an over stock item. The economy was very slow along with boat sales. Some the engines ended up at retail locations and was able to purchase. Incredible performing engine.

shrew · 10-29-2018, 02:32 PM

Quote:

Originally Posted by Calguy

..
Take my word for it...hooked to a Bravo 2....

I never said I doubted that was what was installed in your boat. What I said was I've never seen one. Both statements are mutually exclusive and can both be true.

Calguy · 10-29-2018, 05:59 PM

No problem shrew ...... I should have mentioned the boat was we re powered in my first reply. The EFI and ECM controlled engine has been so reliable and the performance and fuel economy is outstanding. To add, the dry joint, ceramic coated risers alleviate many major service problems of the past.

Ceemee · 07-16-2019, 04:22 PM

Have had my 2400Scr Maxum changed my prop out a few times had a 15 3/4 by 17 stainless steel did well at high speed wouldn’t let me plane at a low speed at all. I switched it to a 14 by 16 4 blade and I can get on plane at lower speeds but I get a less of top speed ! Anyways you don’t run WOT past a few minutes we cruise at 25 I can push it to 40.

NickNick · 07-16-2019, 09:41 PM

Hey Ceemee
I purchased my 96 Maxum when it had about 15 hours on it. The prop at the time was a 17 pitch aluminum and the boat had a hard time getting on plane with a full gas tank and 4 adults aboard. I ended up going to a 15" stainless prop. The boat will not plane until about 3200rpm at around 24 mph now. It has the 5.7 liter 2 barrel engine with an Alpha1 gen2 drive. I spoke to many persons about drive ratio and stuff but never was able to find if that was indeed "normal". The ratio is correct by the way.

I mostly ride with only one other person so I just got used to it. I don't remember what the wide open rpm is now but it doesn't over rev at a top end of 38mph.
I considered changing the intake to a 4-barrel or fuel injection but never did. The thought was to get more horse power at a lower rpm.

Happy boating!
Nick

Ceemee · 04-02-2021, 04:32 AM

[QUOTE=NickNick;59120]Hey Ceemee
I purchased my 96 Maxum when it had about 15 hours on it. The prop at the time was a 17 pitch aluminum and the boat had a hard time getting on plane with a full gas tank and 4 adults aboard. I ended up going to a 15" stainless prop. The boat will not plane until about 3200rpm at around 24 mph now. It has the 5.7 liter 2 barrel engine with an Alpha1 gen2 drive. I spoke to many persons about drive ratio and stuff but never was able to find if that was indeed "normal". The ratio is correct by the way.

I mostly ride with only one other person so I just got used to it. I don't remember what the wide open rpm is now but it doesn't over rev at a top end of 38mph.
I considered changing the intake to a 4-barrel or fuel injection but never did. The thought was to get more horse power at a lower rpm.

Happy boating! Hello Nick My motor was replaced in 2013 with a 350 mag mpi fuel injection carb alpha 1 gen 2.. My 2400SCR 1997 is fully restored in 2021 from front to back in and out as well. My lower unit rebuilt new by mercruiser same as motor. We just finished rewiring whole boat. I still have the prop 14x16 4 blade but we went back to stainless steel. I get on plane at lower speed but lose a little at WOT. We are trying a 14 3/4 x 17 tomorrow 4 blade stainless steel right now i’m at 5000 rpm at WOT if we don’t like it we will go back to the 15 3/4 x17. With the 15 3/4 x 17 my WOT is 48 thats 2 people flat with full tank of gas and cooler. With the 14 x 16 i’m at 43 WOT. Now that’s not me fastest i had the boat was 40 the dealer tested it rated it I did not. I’m handicapped so going fast i don’t like to i’m a cruiser type 20-24 top for me. With the 14x16 plane at 15 with the 15 3/4 x 17 at 20 mph. I had the boat at 40 another boater grandchild cut himself good we raced him to shore met with the ambulance my wife’s a surgical nurse stabilized him.. Hopefully by now you have your issues resolved if not leave a note here i’ll check back we can swap emails i know fantastic people that can help you out if i cannot there all certified mercruiser specialist too...

djones0154 · 04-02-2021, 12:02 PM

I have a 5.0 L Alpha 1
I had issues with getting on plane with six adults. 4-bladed prop made the difference. must get prop to run WOT in rpm range, that time to get correct prop. I also use trim tabs to help. start with them up and as boat is up to plan speed, toggle the both down and then boat jumps up on plane. can adjust back up a bit until boat is sitting nice.

NickNick · 04-03-2021, 04:40 AM

Thanks! I will look into 4 bladed props. I’m not worried about speed, but I do want the engine to spin at the correct RPM while at full throttle. I think my engine is over propped a little and “lugging” a bit.
The highest RPM for my 96 2400 SCR is currently 4800. That is pretty low for the 5.7 liter engine.
Nicknick