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Old 11-03-2012, 10:54   #16
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Re: Cooler Engine Intake Air

A bit sceptic to most opinions.. Any diesel to run properly and have a long problem free life needs a lot of fresh cool air.. IMHO
thou if you use it to get of the pier and load batteries 30min at ones a day.. lets say some 20 days a year who cares..
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Old 11-03-2012, 11:54   #17
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Re: Cooler Engine Intake Air

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Originally Posted by klem View Post
Regarding testing the horsepower of an engine, you can actually get a very precise measurement. The test stands that I used to work on used a torque meter with an accuracy of .2% of full scale and a magnetic pickup for rpm which are extremely accurate. We would double check this number against an S-beam load cell at a known radius on the dyno. There are some standards for how accurate the measurements need to be and then it really comes down to how tight the tolerances are on critical components in the engine that determine the horsepower.
Our primary product is mileage and EPA dynos. We are accurate to 0.05% advertised but we are better than that in reality. That aside, you never know what the dyno accuracy is if the goal is only to name-plate for political purposes.

Its definitely better to run denser air into the engine. Unless your diesel can modulate fuel flow in proportion to air density the fuel injection volume may be the same per stroke regardless of the air mass injested. If you want denser air you only have two choices. Cold air or a turboboost. Keep the air filter clean for sure.

I would be concerned about the potential damage of jpermitting salt air in the motor. You could duct air from a cool space of the boat but use a very large duct to minimize the pressure drop in a long suction line.
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Old 11-03-2012, 12:18   #18
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Re: Cooler Engine Intake Air

Again your talking about apples and oranges !! if you have a BIG auxilary diesel eng of say 80 or 90 hp (like a leyman) if you cool the engine room down even 20 or 30 degrees or more even more what are ya gonna gain?? 1 or 2 hp?? so what ! as long as the engine room is not burning up, your ok !! if your running for hours at a time, you watch the temp gauge to make sure your engines running in the proper temp range don't ya ?? if you don't have a temp problem !! Give it a rest ! theres lots of things that need fixin ! there aways is !! LOL Maybe ya need to wax the bottom to help the boat slip thru the water easier!! then the engine will run cooler !! LOL Just kiddin
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Old 11-03-2012, 12:27   #19
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Re: Cooler Engine Intake Air

We have a 2 cycle Detroit, and a controllable pitch propeller, the engine brings air into the watertight engine room from outside via ducts with fusable link fire shutters and flashback gauze. The only time we noticed excessive engine room temperatures was when the damn automatic fire extinguisher went off.
I would let the engine exhale the hot air, and bring the fresh air in at the furthest point, to reduce overall engine room temp, better for all the ancillary equipment, the sea cools the engine, but what cools the alternator etc?
I think that the difference in power due to charge air temp will be unimportant in this application, far less than say, a dirty prop or bottom.

Just sayin'
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Old 11-03-2012, 12:51   #20
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Re: Cooler Engine Intake Air

Bobconnie & Sy gilana - does seem like a pointless worry. Ours is 115 HP Westerbeke. The engine room is hot and the reason to ventillate is purely for comfort. It stays darn hot long after the engine is shut down. No surprise with a massive hunk of hot cast iron. You raise great points about keeping electronics cool.

Under power we manage our speed, rpm, throttle, and Hundested variable pitch prop to keep the engine temp below 190 to 200. Love that prop. Its a fuel saver and a great help in tight waterways & docking.
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Old 11-03-2012, 16:53   #21
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Yanmar's Larry Berlin mentioned during their three day course that the engine room should not get above 97 degrees. I had always wondered what the blower was for on a diesel boat.
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Old 11-03-2012, 16:57   #22
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Re: Cooler Engine Intake Air

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Yanmar's Larry Berlin mentioned during their three day course that the engine room should not get above 97 degrees. I had always wondered what the blower was for on a diesel boat.
Good luck with that!! We've got two exhaust fans in the engine space, and pull air from the bilge where it should be cooler. Motoring for several hours in the tropics in august will elevate temps to 120 or so.
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Old 11-03-2012, 17:13   #23
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Re: Cooler Engine Intake Air

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I'm with Bob and Connie on this one, i have been around diesels most of my adult life as a mechanic. and as a diesel is a compression ignition engine(meaning it ignites by raising the air temp inside the cylinder)the warm air is a benefit.
Only if you want performance boost on land would you use a Turbo Intercooler.
For additional air to compartment consider a snorkel air intake.

P.S. i just like icons.....
Well . . my boat's engine has a turbo and seawater-cooled intercooler. It's not only for land.

Cooler air means denser air means more mass of air in the combustion chamber, which means a greater mass of fuel can be burned, for more maximum power.

Warm intake air is NOT of any benefit at all to a diesel engine -- it's all bad.

Someone said it only affects maximum power -- this is not true. It affects maximum power at any given RPM level. So with hot intake air, you may need more RPM to get your cruising speed power level you need. Like I said -- hot intake air is all bad. Although in most cases not worth making a big project out of -- as Bob&Connie said.

My boat has multiple large ducts and blowers to keep fresh air moving through the (sealed and soundproof) engine space.
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Old 11-03-2012, 17:15   #24
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Re: Cooler Engine Intake Air

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Originally Posted by Safari38LH View Post
Yanmar's Larry Berlin mentioned during their three day course that the engine room should not get above 97 degrees. I had always wondered what the blower was for on a diesel boat.

Wow. we're gonna have to give up plans to sail south of Hatteras.
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Old 11-03-2012, 18:00   #25
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Re: Cooler Engine Intake Air

Heck in Louisiana from April thru late Nov. we could never run a engine if we have to stay under 97 degrees !!even with big blowers and vents !!
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Old 11-03-2012, 21:33   #26
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Re: Cooler Engine Intake Air

I agree with earlier comment with regards to bringing in salt air to the engine intake.
I have 2 4" ducts with blowers to suck hot air out when temps rise.
considering ducting air intake down low to the dry bilge where air is coolest
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Old 12-03-2012, 22:03   #27
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Re: Cooler Engine Intake Air

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I agree with earlier comment with regards to bringing in salt air to the engine intake.
I have 2 4" ducts with blowers to suck hot air out when temps rise.
considering ducting air intake down low to the dry bilge where air is coolest

I wonder if there is a bennefit to ducting air inlet over the alternator to help keep it cool. Inlet air will be warmer - but how much is an alternator$$

My engine room has a dorade like intake box on the cabin side so I can choose outside air.
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Old 12-03-2012, 22:12   #28
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Re: Cooler Engine Intake Air

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Yanmar's Larry Berlin mentioned during their three day course that the engine room should not get above 97 degrees. I had always wondered what the blower was for on a diesel boat.
Haha.

If thats true then half of the summer we'd have to run AC in the engine room since its 110 F in the sun and 90 F in the shade.
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Old 12-03-2012, 22:41   #29
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Re: Cooler Engine Intake Air

Obviously cooler air is more oxygen rich, as is air with high moisture content.
I doubt very much that anyone short of an ocean going tug is going to notice the benefits of a few degrees cooler engine intake air, as you are traveling through a fluid medium all of your progress is relative to the mediums constant changing state.

As to benefits of warm air, i have worked on large diesel equipment in sub zero temperatures and they are a bitch to get running when the intake air is cold. which is why we would have to resort to ether bombs to assist in starting the engine.


As a diesel is a Compression ignition engine,it fires by compressing the air inside its cylinders until the oxygen ignites the fuel charge, hot intake air will aid in raising the combustion chamber charge.
As you have stated, to develop your maximum horsepower at a given RPM Cooler air will indeed provide more oxygen, but again because of the Fluid medium you are moving through, the difference would be very marginal.

If the engine room was pulling air from the gates of hell i could see your point. However.. as long as you have a fresh supply of clean air to your engine spaces then air temperature in the normal range will do just fine.

"QUOTE=Dockhead;906626]Well . . my boat's engine has a turbo and seawater-cooled intercooler. It's not only for land.

Cooler air means denser air means more mass of air in the combustion chamber, which means a greater mass of fuel can be burned, for more maximum power.

Warm intake air is NOT of any benefit at all to a diesel engine -- it's all bad.

Someone said it only affects maximum power -- this is not true. It affects maximum power at any given RPM level. So with hot intake air, you may need more RPM to get your cruising speed power level you need. Like I said -- hot intake air is all bad. Although in most cases not worth making a big project out of -- as Bob&Connie said.

My boat has multiple large ducts and blowers to keep fresh air moving through the (sealed and soundproof) engine space.[/QUOTE]
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Old 13-03-2012, 01:25   #30
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Re: Cooler Engine Intake Air

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one thing i've noticed on many production yachts that have engine room blowers is that often they are set up to extract air from the engine room!

this seems counter productive,since the engine it self is a large extractor fan!!
True however on all large boats i've built we have always sized ER Fans to give a positive pressure in the space, always get the rush of air outwards upon opening the door if not the fan is U/S.

Cold air venting into the bilge with a vent at the deckhead is the norm, but as you say there are one or four big diesel pumps sucking it out of the space.

Cheers
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