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New mercury 400 RPMs ?

Old 08-26-2020, 05:17 AM
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Default New mercury 400 RPMs ?

Decided to ask this question in a new thread due to so many people who just clutter up these threads with negative comments.
One of the culprits were looking at as a potential reason for our lower unit failures is the boat being over propped. Im just wondering what you guys with 400s are running for props, and what RPMs you get out of the motor at full throttle. Weve never seen anything above 5500.
Old 08-26-2020, 05:35 AM
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So you have 400"s now and keep blowing lowers? How many over what period of time?
Old 08-26-2020, 05:39 AM
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Per Mercury's website, it states wide open RPM's as 6200-6800 for the 400. The 400r states 6400-7000.

Think it is safe to say you are way over propped.
Old 08-26-2020, 05:40 AM
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Itís sounds like youíre very very overpropped... you should be up around 6800 I believe on that motor.

Thatís also the rpm range that give a the extra hp over the 350.


edit: PF beat me to it.
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Old 08-26-2020, 06:01 AM
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With 91octane fuel, they should be getting to 6800rpm with a light load in cooler weather. Loaded and during the heat of the summer, 6200rpm is more likely where you’ll be.
Old 08-26-2020, 06:05 AM
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I was seeing 6500 last weekend running with a fishing load (4 guys).

I run with Rev 4 XPs, 14.6 x 21.
Old 08-26-2020, 06:29 AM
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Mercury says to be in the upper half of the RPM WOT range with the boat loaded.

If the WOT Range is 6200 ~ 6800 then you should be above 6500 RPM. Motor trimmed up only to the point of best efficiency and no further.

Over loading a propeller is over loading the motor and also over loading the gear set.

You could very well be on to something to do with your experiencing an excessive number of lower unit failures.
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Old 08-26-2020, 08:24 AM
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Thats what we're thinking now. The boat has never seen a number with a 6 infront of it.

QUOTE=Texas 17;13988753]Itís sounds like youíre very very overpropped... you should be up around 6800 I believe on that motor.

Thatís also the rpm range that give a the extra hp over the 350.


edit: PF beat me to it.[/QUOTE]
Old 08-26-2020, 08:27 AM
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Yep, would love to know what props other guys with big CC are running with these motors. I really think we are way over propped which could be causing this.

QUOTE=alloyboy;13988922]Mercury says to be in the upper half of the RPM WOT range with the boat loaded.

If the WOT Range is 6200 ~ 6800 then you should be above 6500 RPM. Motor trimmed up only to the point of best efficiency and no further.

Over loading a propeller is over loading the motor and also over loading the gear set.

You could very well be on to something to do with your experiencing an excessive number of lower unit failures.[/QUOTE]
Old 08-26-2020, 08:28 AM
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Yep, thats what were thinkng, and yet weve never seen a number with a 6 infront of it.


Originally Posted by davidwademarine View Post
With 91octane fuel, they should be getting to 6800rpm with a light load in cooler weather. Loaded and during the heat of the summer, 6200rpm is more likely where youíll be.
Old 08-26-2020, 08:59 AM
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Way overpropped. You would be overpropped at that RPM with the 300 V8 which is supposed to turn 6000.
What boat is this? How many engines? And what prop is currently on them?
Old 08-26-2020, 10:13 AM
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Originally Posted by fishcop View Post
Yep, thats what were thinkng, and yet weve never seen a number with a 6 infront of it.
I think the outboards can't even pass the dealer PDI without being propped within mercury specs. So your boat should have never been handed over to you. But this is just my understanding....
Old 08-26-2020, 10:22 AM
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PDI performed with one guy and half or less tank of gasoline. Boat gets put into service and everything changes.

Which is why the owner's manual applies to the owner. Not the dealer PDI man.
Old 08-26-2020, 10:30 AM
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Originally Posted by alloyboy View Post
PDI performed with one guy and half or less tank of gasoline. Boat gets put into service and everything changes.

Which is why the owner's manual applies to the owner. Not the dealer PDI man.
yes but his maximum rpm was so low, 5500, I am guessing it didn't reach spec with just one guy.
Old 08-26-2020, 11:10 AM
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Originally Posted by willy13 View Post
yes but his maximum rpm was so low, 5500, I am guessing it didn't reach spec with just one guy.
You could be right.
Old 08-26-2020, 07:28 PM
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I run Rev4 XPís, 24P. Donít remember the exact top end RPMs. Iíll check next time out.
Old 08-26-2020, 07:33 PM
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I’m running quads 400M on a 39 with Bravo FS 27 and with full gas, water, luggage, and 6 people tops between 6200 to 6500 rpms
Old 08-28-2020, 06:38 AM
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Its a 42 yellowfin with 16 x 19p

QUOTE=DeepImpact;13991705]Iím running quads 400M on a 39 with Bravo FS 27 and with full gas, water, luggage, and 6 people tops between 6200 to 6500 rpms[/QUOTE]
Old 08-28-2020, 06:39 AM
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Boat is a 42 yellowfin, popped two in the last 50 hours. Both counter rotators

Originally Posted by OffshoreApparel.com View Post
So you have 400"s now and keep blowing lowers? How many over what period of time?
Old 08-28-2020, 08:09 AM
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either you are 6" over propped, not trimming the motors, or dragging an anchor

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