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Old 02-04-2018, 05:47 PM   #1
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Max rpm for Volvo D4-300

On my ST44 my engines were topping out at 3450 and 3400.

I got a prop fixed at a local shop, who said the rake was off by 3/4".

Now I have one engine at 3450 and the other at 3630, almost 200rpm higher for the Angie running the repaired prop.

Both props were fixed about 1.5 years ago after striking an object. I only sent one in recently as I thought it was the cause of some vibration.

Anyways, any thoughts? I'll probably have them pull the other one and fix it as well.

Also, what rpm does your ST44 max out at?

Thanks!
Mike
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Old 02-04-2018, 06:55 PM   #2
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Well first, how are you measuring rpm. If with a dash tach, they are often unreliable. Measure the rpms with a phototach- less than $20 at eBay or Amazon.

Since the Volvo D4 is rated to make its 300 hp at 3,500 rpm, that is the minimum you want to run at wot, and preferably 3,600 rpm. If your tachs are accurate, one engine is over propped.

David
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Old 02-04-2018, 10:42 PM   #3
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Mike,

Not a direct answer but perhaps of some use...I realize you have a much bigger and inboard boat.

My D4-260 was rated for WOT 3400-3700. Initially it was propped for about 3450 with a full-load. We went "down" in pitch one propeller set (outdrive) which gave us 3650 at WOT. After the change, she really felt better all through the RPM range, and especially at cruise. My expert technician was very happy to see us make the change, as well. So I recommend trying to stay at the top of the recommended WOT range.

Good Luck
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Old 02-04-2018, 10:54 PM   #4
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Mine are hitting 3650 but one engine's turbo boost is 5 psi lower than the others... anyone else seeing that difference on their turbos?
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Old 02-05-2018, 12:01 AM   #5
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I'm going by my dash tach and it had shown 3450 before the prop fix and now shows 3630.

I do have one turbo that shows 4 to 5 psi higher but they even out at WOT.
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Old 02-06-2018, 08:25 AM   #6
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My turbo pressure is about 1/2 psi out between the engines. I thought this could be the gearboxes, one running in reverse taking more power?
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Old 02-06-2018, 09:23 AM   #7
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I would get the owners manual and look up the maximum RPM. Your props should allow the engines to reach that speed.

That's what my book says.
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Old 02-06-2018, 09:26 AM   #8
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D4 should have a digital tach readout on the engine display. Use that for rpm data, it should be dead accurate.

You should have had both props scanned even though only one needed repair. Then with both in the shop they could have matched the pitch exactly.

For a 3500rpm engine, I would target 3550 as desired full power rpm. Prop shop will need that as well as the rpms you get now.
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Old 02-06-2018, 11:12 AM   #9
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Quote:
Originally Posted by Ski in NC View Post
D4 should have a digital tach readout on the engine display. Use that for rpm data, it should be dead accurate.

You should have had both props scanned even though only one needed repair. Then with both in the shop they could have matched the pitch exactly.

For a 3500rpm engine, I would target 3550 as desired full power rpm. Prop shop will need that as well as the rpms you get now.


Yes, I definitely should have done that. Oh well. I did ask the prop shop about this after the fact and they said since they scanned the prop they can just match the other one to the one they fixed.

I also checked with an authorized Volvo service center and they show that max rpm should be 3600.

Lastly, I used the digital tachs on the EVC panel.

Thanks,
Mike
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