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Old 06-06-2017, 02:29 PM   #1
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Default Mercruiser 5.0 230 BHP

What's the safe operational rev range of the Mercrusier base engine (5.0l) with Alpha drive fitted in the Maxum 2400SCR - its a 2004 model.

Reason I ask is a friend has a decent size Cranchi with 2 x Turbo Diesels and he can top out at just over 4,000 rpm.

My SCR seems to run out of puff at around 3,000 revs, I/E it wont go any higher than that - is that normal ?

Perhaps the throttle control is wrongly calibrated ??
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Old 06-06-2017, 04:07 PM   #2
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The 5.0 should have a WOT (wide open throttle) of 4400-4800 rpm, however should only be ran at this rpm for a very short time. Normal cruise rpm for this engine and boat should be 3000-4000 rpm.

If overproped, too much pitch you will not be able to achieve proper rpm. A dirty bottom will also cause this or a tired engine.
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Old 06-06-2017, 04:32 PM   #3
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thanks.

which then asks the question, and forgive me but new to this, what's the standard / correct size and pitch of prop for the boat and engine ?

And what sort of performance would it achieve with the standard prop - I don't seem to be able to get anything more than around 25/27 MPH at just less than 3,000 RPM with the trim set ?
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Old 06-06-2017, 05:28 PM   #4
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Basic principle is to have a prop (pitch/dia/etc) that allows the engine(s) to achieve proper operating range. In your case, The 5.0 should have a WOT (wide open throttle) of 4400-4800 rpm. Small variances in prop types (combo of style/# blades/dia/pitch/etc) allow for the fine tuning to certain goals. Ex: 4 blade tends to provide better hole-shot but a slightly reduced top-end. Both should still be operating in the suggested range!

Speed will be an output from the proper matching of prop & engine, not an input.

Many of the Maxum's seem to be over-propped by the dealers or previous owners under the assumption that more pitch = more speed.

I just reduced the pitch (2 in) on my setup (3000 SCR, 5.0L BII) to achieve the WOT called for. Speed dropped only 1/2 knot, but the engines are happier operating in their proper rpm/power band.

In summary, there is no "standard" prop that satisfies all conditions.
Landing on the "right" prop requires that you measure current performance (WOT RPM) with a tuned engine, normal load (gas/people/beer?).

Rule of thumb to get started would be to add (or subtract) 1in of pitch for each 200 rpm needed to get to the desired WOT.

In my case, I was overpropped (WOT was only 4200). I needed to remove 2in pitch to get to the 4600 I targeted as my WOT goal.

Hope this helps..
For each 200 RPM needed to get to desired WOT rpm
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Old 06-06-2017, 09:23 PM   #5
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Hi All!
I have a 1995 2400 SCR with a 5.7 235HP A1 G2 and it came with a 14.5 X 17p prop!
Hope that helps!
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Old 06-06-2017, 10:08 PM   #6
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No such thing as a standard prop size. Its size is based on the engine, hull length, beam, chine, .... weight. Others have provided inputs on what they are using but you can also try mercruisers prop calculator to see what it suggests.
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