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Old 04-03-2021, 12:30 PM   #61
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B&B
Good reply.
Perhaps it only needed 1500 before, and at 1650 slippage robbed additional speed.
Anyway the old filters were saturated with oil and crud so it was time to renew one way or another.
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Old 04-03-2021, 12:31 PM   #62
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Originally Posted by backinblue View Post
Did anything else change? That sounds "fishy" to me. lol. Not disputing what you experienced, but here's my take. A better filter may allow you to gain more HP, but your props are spinning at a speed in proportion to your engine RPM. Your boat speed should depend on how fast your props are spinning, not how much horsepower it takes. So whether it takes 400 HP or 500 HP to spin your props at a given RPM, your props don't know the difference and your boat speed should be directly related to your prop speed and engine RPM. Sounds like something else was in play like wind or current or cleaner bottom or less weight on board (fuel and water etc).

Where an air filter would make a difference, if WOT got you to 3000 RPM and now gets you to 3100, that could mean you are now making more HP and able to spin the props faster. Similarly, if your GPH went down for the same RPM, your engines are now more efficient than before (i.e. using less fuel to create the same RPM because there is less air resistance from your filter allowing your engine to spin more freely)

I'm sure there are others who will tell me I'm all wet (pun intended again), so I'll look forward to feedback.
I believe this is what Smitty said in his shorthand.
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Old 04-03-2021, 03:56 PM   #63
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Thanks for the worthless reply.
"Whereas before 1650 RPM was needed to achieve 7.5 to 8 KN, now it only needs 1500 RPM."
Please describe how the condition or existence of an air filter would affect the amount of rpm required to reach 7.5 knots?
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Old 04-03-2021, 04:12 PM   #64
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"Whereas before 1650 RPM was needed to achieve 7.5 to 8 KN, now it only needs 1500 RPM."
Please describe how the condition or existence of an air filter would affect the amount of rpm required to reach 7.5 knots?
There is now more air in , therefore more air out the exhaust giving it a boost.
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Old 04-03-2021, 05:06 PM   #65
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There is now more air in , therefore more air out the exhaust giving it a boost.
I now understand your problem.
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Old 04-03-2021, 07:05 PM   #66
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B&B
Good reply.
Perhaps it only needed 1500 before, and at 1650 slippage robbed additional speed.
Anyway the old filters were saturated with oil and crud so it was time to renew one way or another.
Clean filters are always a good thing, whether there's a noticeable difference or not.
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Old 04-05-2021, 10:51 AM   #67
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AIRSEP installed on DDC 4-71 Natural

Walker makes a kit to upgrade the older DDC 4-71 Naturally Aspirated engines. Easy to install but there a few engine differences that you need to share with them to see if you can just remove he "Oil Bath" setup, or if you need an adapter if removing the "Farr" rectangular air filter box.


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Old 04-05-2021, 11:42 AM   #68
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Backinblue,
Check out Tony Athens website for some info on CCV systems. https://www.sbmar.com/articles/crankcase-ventilation/
Also you might find the following article, written mainly about his ideas relating to Cummins engines, but the general principles of what a good CCV system should accomplish apply. https://www.sbmar.com/articles/envir...arine-diesels/
To me, his basic concept of "letting gravity" do most of the work, capturing the excess liquid rather than pushing it into the turbo, aftercooler, and then engine, makes total common sense.
To be clear, I installed one of his Envirovent systems on my Cummins, replacing the Walker Airsep. The difference was amazing. With the Walker (factory installed), my turbo and aftercooler had a fair amount of oily "gunk". With the Envirovent, there was no noticeable oily residue in the air side of the turbo. There was also no oily deposits anywhere in the ER (or on the engine) using the Envirovent.
There is one system on his website for a Yanmar, but it might not fit your engine.
I have no affiliation with Tony other than I have gained from the way he freely shares his knowledge and experience, and have been a satisfied customer.
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