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Drawing air from outside engine space


blackrose

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I asked this question some time ago on a related thread, but I'm afraid I forgot the answer...

 

So if those in the know wouldn't mind indulging me again:

 

If I draw cold air for my air filter from outside the hot engine space via a pipe, I understand that this will make my engine run better. However, there was some reason why it wasn't such a good idea to do this? Is it something to do with cold air then not being drawn in to the engine space to cool other things like alternators?

 

Thanks

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Ah, was that it? Ok!

 

 

 

That's what the filter is for!

I think most people felt it was pointless for such a low performance engine. I too had considered doing same after fitting an air filter,

Edited by Guest
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I see, thanks again.

 

Mike

 

I think the reasoning is that cold air is more dense and will therefor have a greater density of oxygen to aid combustion. While this is true and can even be felt in a car in a cold damp driving situation, I very much doubt this would affect a NB engine in any significant way seeing as how our engines are just ambling along most of the time.

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I think the reasoning is that cold air is more dense and will therefor have a greater density of oxygen to aid combustion. While this is true and can even be felt in a car in a cold damp driving situation, I very much doubt this would affect a NB engine in any significant way seeing as how our engines are just ambling along most of the time.

 

I'm moored on the Thames now, so my engine doesn't amble quite as much as it used to.

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The air being drawn into the air filter tends to circulate around the engine bay first, especially if this has been designed in deliberately (a grille in the corner diagonally opposite the filter, for example).

 

Pipe the cold air direct to the filter and the rest of the engine bay will get hotter. As you've said, this can be particularly bad news for alternators.

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I asked this question some time ago on a related thread, but I'm afraid I forgot the answer...

 

So if those in the know wouldn't mind indulging me again:

 

If I draw cold air for my air filter from outside the hot engine space via a pipe, I understand that this will make my engine run better. However, there was some reason why it wasn't such a good idea to do this? Is it something to do with cold air then not being drawn in to the engine space to cool other things like alternators?

 

Thanks

 

 

I agree that it is highly unlikely to make a noticeable difference PROVIDING the engine area has adequate vents. However, for the sake of completeness, we had a lot of problems on the Thames hire fleet (cruisers) with Lister SL4s popping the combustion chamber inserts out of the pistons. We cured this by ducting cold air direct to the intake (before we changed them for BMC 1.5s & 2.2s) and put the problem down to hot air leaking from the engine cowling and "sack cloth" hot cooling air outlet ducts.

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I think the reasoning is that cold air is more dense and will therefor have a greater density of oxygen to aid combustion. While this is true and can even be felt in a car in a cold damp driving situation, I very much doubt this would affect a NB engine in any significant way seeing as how our engines are just ambling along most of the time.

In my case there was another reasoning.

Since the air intake was on the same side as the exhaust, when the wind or you were stuck in locks, it sucked in exhaust fumes and made the exhaust smoke worse.

Blowing fresher air from the opposite side direct to the air intake makes a considerable difference and tends to help convection operate the same way assiting the cooling of alternator and other stuff!

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In my case there was another reasoning.

Since the air intake was on the same side as the exhaust, when the wind or you were stuck in locks, it sucked in exhaust fumes and made the exhaust smoke worse.

Blowing fresher air from the opposite side direct to the air intake makes a considerable difference and tends to help convection operate the same way assiting the cooling of alternator and other stuff!

 

Sounds like a good case for a 12v bilge blower or some other fan next to a vent, wired to come on when the engine starts.

 

My engine space has 2 vents - one on each side of the boat. If I used a bilge blower next to a vent, would it be better to suck air in or blow air out?

Edited by blackrose
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Mike, leave it alone. There must be something else that needs sorting on your boat

 

Richard

 

MORE: Or perhaps it is time to buy a new boat

 

There are lots of things that need sorting on my boat and I'm always interested in trying different ideas.

 

I'll tell you what Richard, if I can tell you what to do on your boat, then I'll let you tell me what to do on mine.

 

Deal?

Edited by blackrose
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There are lots of things that need sorting on my boat and I'm always interested in trying different ideas.

 

I'll tell you what Richard, if I can tell you what to do on your boat, then I'll let you tell me what to do on mine.

 

Deal?

 

No deal. I'm responding to your request for advice

 

My advice would be to leave anything to do with the air going into your engine well alone

 

Richard

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My engine space has 2 vents - one on each side of the boat. If I used a bilge blower next to a vent, would it be better to suck air in or blow air out?

 

I would say suck air in if your going to, mainly due to if the vents arnt big enough for fan and engine they'll be fighting each other.

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Sounds like a good case for a 12v bilge blower or some other fan next to a vent, wired to come on when the engine starts.

 

My engine space has 2 vents - one on each side of the boat. If I used a bilge blower next to a vent, would it be better to suck air in or blow air out?

 

I have this arrangement with an extractor fan sucking the air out. It works well and does not affect the engine breathing at all. It also keeps the engine bay a bit cooler and cleaner. tosher

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we suffered with our bmc getting uncomfartably warm when cruising at higher speeds, this is in an indirectly cooled elysian 27 cruiser. although the main culprit was poorly sized and routed pipework to the raw water pump, a lack of adequate air flow through the engine bay was not helping in the slightest.

 

to resolve this the raw water piping was reworked, extra vents were let into the hull sides just below the gunales, whilst i was at it i ditched the crap mesh intake filter and fitted an air filter assembly from a late 90's hyuandi coupe, its shape lent itself perfectly to my needs.

 

the result of all this is an engine whch keeps its cool at sustained high speed operation, consumes clean filtered air from outside of the engine bay, has a reduced noise level due to intake air being drawn from under the gunale.

 

as an OTT extra i have fitted a 3" flange mount bilge blower that has the intake pipe close to the alternator to draw more heat away from this area on super hot days.

 

if you have the time skills and like tinkering i would duct filtered air to the motor and add extra ventilation to the engine bay, i have always hated the half measures so often seen in boat building.

 

hope this helps.

 

gaz

Edited by gazza
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we suffered with our bmc getting uncomfartably warm when cruising at higher speeds, this is in an indirectly cooled elysian 27 cruiser. although the main culprit was poorly sized and routed pipework to the raw water pump, a lack of adequate air flow through the engine bay was not helping in the slightest.

 

to resolve this the raw water piping was reworked, extra vents were let into the hull sides just below the gunales, whilst i was at it i ditched the crap mesh intake filter and fitted an air filter assembly from a late 90's hyuandi coupe, its shape lent itself perfectly to my needs.

 

the result of all this is an engine whch keeps its cool at sustained high speed operation, consumes clean filtered air from outside of the engine bay, has a reduced noise level due to intake air being drawn from under the gunale.

 

as an OTT extra i have fitted a 3" flange mount bilge blower that has the intake pipe close to the alternator to draw more heat away from this area on super hot days.

 

if you have the time skills and like tinkering i would duct filtered air to the motor and add extra ventilation to the engine bay, i have always hated the half measures so often seen in boat building.

 

hope this helps.

 

gaz

 

I'm beginning to think this approach has a lot to recommend it. A dedicated air supply from outside to the engine and a vent each side of the engine bay with an extract fan to asist the flow across the engine room. Despite people telling me it doesn't matter that much, I get alarmed at how hot my engine space gets after a long slog up river eg.

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agreed richard.

 

your advice is sound,it is unfortunate that it was not readily accepted by someone with less experience than your good self?

 

You're making a few assumptions. You may know about Richard's experience, but how do you know what experience I have to be able to compare? Some others here also with plenty of experience seem to think my suggestion wasn't such a bad idea...

 

No deal. I'm responding to your request for advice

 

My advice would be to leave anything to do with the air going into your engine well alone

 

Richard

 

That's fine Richard, perhaps it was just your comment that perhaps it was time for me to buy a new boat that put my back up. I didn't find that very constructive at all.

 

we suffered with our bmc getting uncomfartably warm when cruising at higher speeds, this is in an indirectly cooled elysian 27 cruiser. although the main culprit was poorly sized and routed pipework to the raw water pump, a lack of adequate air flow through the engine bay was not helping in the slightest.

 

to resolve this the raw water piping was reworked, extra vents were let into the hull sides just below the gunales, whilst i was at it i ditched the crap mesh intake filter and fitted an air filter assembly from a late 90's hyuandi coupe, its shape lent itself perfectly to my needs.

 

the result of all this is an engine whch keeps its cool at sustained high speed operation, consumes clean filtered air from outside of the engine bay, has a reduced noise level due to intake air being drawn from under the gunale.

 

as an OTT extra i have fitted a 3" flange mount bilge blower that has the intake pipe close to the alternator to draw more heat away from this area on super hot days.

 

if you have the time skills and like tinkering i would duct filtered air to the motor and add extra ventilation to the engine bay, i have always hated the half measures so often seen in boat building.

 

hope this helps.

 

gaz

 

Thanks, it does indeed.

Edited by blackrose
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