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Old 24-05-2022, 08:34   #1
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Turbo Power Output Vs Engine Hp

Hi
I am just after buying a boat from overseas. It arrives here Saturday. One of the questions I asked the previous owner was what his top speed was. Anyhow I did not think it was great so start researching a turbo. The engine is a yanmar 4jh2ute. The engine is rated 73kw or around 95hp. On looking at the recommended turbo I noticed that it's max output is 77hp.
So I am confused how a turbo output of 77hp can be on a 95hp engine. I am not experienced enough to know how turbos are matched to engines but this seems strange to me.

Any member know why this may be or am I making an error in my thinking

Thanks
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Old 24-05-2022, 11:17   #2
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Re: Turbo Power Output Vs Engine Hp

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Originally Posted by sliproad View Post
Hi

I am just after buying a boat from overseas. It arrives here Saturday. One of the questions I asked the previous owner was what his top speed was. Anyhow I did not think it was great so start researching a turbo. The engine is a yanmar 4jh2ute. The engine is rated 73kw or around 95hp. On looking at the recommended turbo I noticed that it's max output is 77hp.

So I am confused how a turbo output of 77hp can be on a 95hp engine. I am not experienced enough to know how turbos are matched to engines but this seems strange to me.



Any member know why this may be or am I making an error in my thinking



Thanks

This site indicates the UTE was 99hp.
https://boatdiesel.com/Engines/Yanma...bilePortrait=1

Not clear exactly what you question is.
Are you asking about the specific turbo used?
Are you wandering why a turbo intended for a 77hp motor is on a 95/99hp motor?
If the latter then maybe it’s because without the turbo it would be a 77hp motor naturally aspirated.
Or it may be that a turbo optimized for a specific power can be used on engines with different but not very different powers.
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Old 24-05-2022, 11:40   #3
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Re: Turbo Power Output Vs Engine Hp

Hi
I am really not sure what I am talking about. The turbo listed is RHB52HW. Now I have read somewhere that this turbo max output is 77HP. I am not sure if the information that I read is correct. My confusion comes from this. 95-99 hp with a turbo max at 77hp.
As I have said the information may be not be correct regarding turbo output. I think the base engine without the turbo is 55hp.
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Old 24-05-2022, 11:42   #4
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Re: Turbo Power Output Vs Engine Hp

Maybe 77hp is the max HP is can add to a base engine output.
Is this a curiosity question or is the a specific problem you are trying to work thru?
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Old 24-05-2022, 11:50   #5
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Re: Turbo Power Output Vs Engine Hp

The reason I am asking is that there is another turbo for a different model that's 125 hp. I am considering using that. I can't understand why the turbo output would be less than stated HP of engine. As I understand max output of the turbo is the max HP the engine can achieve. IE base is 55HP with a 77hp output turbo.
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Old 24-05-2022, 12:00   #6
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Re: Turbo Power Output Vs Engine Hp

It maybe that the turbo max output figure 77HP is wrong which would probably clear it up for me.
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Old 24-05-2022, 12:51   #7
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Re: Turbo Power Output Vs Engine Hp

I plugged in the turbo number you gave and the few hits I got suggested it was for an 88hp motor.

Might be over the years, they did minor tweaks that changed the HP.

I had an old 1st generation non-turbo Ford 7.3 diesel with a whopping 180hp. The last of the 7.3s was 275hp.

So what is the top speed?
What is the boat?
Is the bottom clean?

Displacement boats are typically limited by hull speed, so a 35ft boat topping out around 7kts is not a sign of a problem.

Also, it's amazing how much impact a dirty bottom can have. A little growth might cut 0.5kts off your speed and bad growth can take 1-2kts off your speed.
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Old 24-05-2022, 13:11   #8
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Re: Turbo Power Output Vs Engine Hp

I am not fully sure of the condition of the bottom or engine health, It's a beneteau Antares 655. It's topped out at 9knts. I am looking at options about this engine. I know about the cleaning of the hull so on. When researching the turbo I came across this. Even if 88hp that is the max output of the engine so I am trying to figure out where the hp comes from to bring it up to 99Hp.
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Old 24-05-2022, 14:14   #9
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Re: Turbo Power Output Vs Engine Hp

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Originally Posted by sliproad View Post
I am not fully sure of the condition of the bottom or engine health, It's a beneteau Antares 655. It's topped out at 9knts. I am looking at options about this engine. I know about the cleaning of the hull so on. When researching the turbo I came across this. Even if 88hp that is the max output of the engine so I am trying to figure out where the hp comes from to bring it up to 99Hp.
Might be the same engine from a different year.

As with my Ford example...180hp to 275hp with the same basic engine.

The turbo itself does not have a HP but affects how much HP the engine can produce.

So basically an 18ft planing power boat. Sounds like it's not getting on plane, in which case, 9kts is likely just plowing along making big waves but not a lot of speed. Without getting on plane, that's not an unexpected top end.

Is it overloaded? My BIL had a 28ft cuddy cabin and had to have the passengers all move forward to help it get up on plane because it was under powered. Likewise a dirty bottom or damaged prop could make it difficult to get up on plane.
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Old 24-05-2022, 14:34   #10
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Re: Turbo Power Output Vs Engine Hp

Hi Valhalla
Not sure of anything at the moment I will know more when I get my hands on it. Top end speed seems a bit low to me maybe 25 - 50 % low, but could be down to engine wear or anything. I know I can sort all that out hence research the Turbo. This brought me to this question regarding the HP. Still can't get my head around it. I will have to go to a turbo shop to see what their thoughts are. As far as I understand the turbo can only create certain amount of HP.
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Old 24-05-2022, 14:36   #11
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Re: Turbo Power Output Vs Engine Hp

According to all documents the engine is 73kw.
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Old 24-05-2022, 16:09   #12
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Re: Turbo Power Output Vs Engine Hp

What is the boat? Make & model?
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Old 24-05-2022, 16:14   #13
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Re: Turbo Power Output Vs Engine Hp

Hi
I found my answer. I have a manual that says RHB52HW after some research it's actually RHB52W which has 100 HP output. Now if I could find a CHRA for a RHB52W I would be delighted.

Thanks for the help
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