The Murphy Builders Site

More help needed.I have a 160 HP with crossover exhaust & two mufflers with heat shrouds.Plan on using both for cabin heat.Going to use a shroud on the crossover pipe for carb heat.My question is should i take the intake air for the mufflers from the back off my engine baffels or cut a intake in the nose bowl.Also the heat boxes i have for cabin heat just lets the heat from the system dump out under cowling when heat in not on.Should i have heat boxes with no dumping off hot air when heat is not on.If all this air is passing over engine & not going down through cylinders just passing straight out the two 2 " holes in rear baffels will this loss off air affect cooling off enging.Little confusing i know but would like to do this correct the first time.



Regards: Alvin
Rebel. 776



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You must have air flow thru the shrouds either using it for heat or dumping
it....or you will overheat the shrouded in section of the mufflers. I prefer
to take the inlet off the front baffle plate between the front cylinder(s)
and the cowl nose bowl. Taking from the rear baffle steals some + pressure
off the baffles..and why I also don't like rear baffle mounted coolers
either.

Wayne

----- Original Message -----
From: "Alvin and Glenys Adams" <gander.electrical@nf.sympatico.ca>
To: "rebel" <rebel-builders-d@dcsol.com>
Sent: Wednesday, February 01, 2006 11:01 PM
Subject: Cabin Heat Syatem.

More help needed.I have a 160 HP with crossover exhaust & two mufflers

with heat shrouds.Plan on using both for cabin heat.Going to use a shroud on
the crossover pipe for carb heat.My question is should i take the intake air
for the mufflers from the back off my engine baffels or cut a intake in the
nose bowl.Also the heat boxes i have for cabin heat just lets the heat from
the system dump out under cowling when heat in not on.Should i have heat
boxes with no dumping off hot air when heat is not on.If all this air is
passing over engine & not going down through cylinders just passing straight
out the two 2 " holes in rear baffels will this loss off air affect cooling
off enging.Little confusing i know but would like to do this correct the
first time.

Regards: Alvin
Rebel. 776



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Alvin,

I've uploaded some pics to (210 - R-Engines). I used this type of system on our Lyc 160 hp 0320. Heater worked fine. Air intake from the front of engine baffle system (FRESH AIR), and no compromise to +pressure in the cowl for engine cooling.

Jeff


----- Original Message -----
From: Alvin and Glenys Adams <gander.electrical@nf.sympatico.ca>
Date: Wednesday, February 1, 2006 8:01 pm
Subject: Cabin Heat Syatem.

More help needed.I have a 160 HP with crossover exhaust & two
mufflers with heat shrouds.Plan on using both for cabin heat.Going
to use a shroud on the crossover pipe for carb heat.My question is
should i take the intake air for the mufflers from the back off my
engine baffels or cut a intake in the nose bowl.Also the heat
boxes i have for cabin heat just lets the heat from the system
dump out under cowling when heat in not on.Should i have heat
boxes with no dumping off hot air when heat is not on.If all this
air is passing over engine & not going down through cylinders just
passing straight out the two 2 " holes in rear baffels will this
loss off air affect cooling off enging.Little confusing i know but
would like to do this correct the first time.



Regards: Alvin
Rebel. 776



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Wayne:

You may well be right about ventilation of the carb heat shrout being a
"must", but I don't have it, and have 30+ hours on the airplane without any
evident problems so far, so I'd like to be sure before changing anything.

How do you know the shrouded area overheats? How hot is too hot? It seems
to me that on many tightly cowled airplanes they insulate the exhaust to
prevent heat loss to surrounding structure. The carb air shroud is quite a
ways from anything up the front of an O320/360 in the Murphy installation,
and it's not going to get any hotter than the exhaust pipe itself otherwise
would, so I don't think that's a problem. So the problem would have to be
with the shrouded portion of the exhaust itself, which would have to get hot
enough to deform, presumably. How hot does/can that get?

Al





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At 07:56 AM 2/2/2006 -0500, you wrote:

Wayne:

You may well be right about ventilation of the carb heat shrout being a
"must", but I don't have it, and have 30+ hours on the airplane without any
evident problems so far, so I'd like to be sure before changing anything.

How do you know the shrouded area overheats? How hot is too hot? It seems
to me that on many tightly cowled airplanes they insulate the exhaust to
prevent heat loss to surrounding structure. The carb air shroud is quite a
ways from anything up the front of an O320/360 in the Murphy installation,
and it's not going to get any hotter than the exhaust pipe itself otherwise
would, so I don't think that's a problem. So the problem would have to be
with the shrouded portion of the exhaust itself, which would have to get hot
enough to deform, presumably. How hot does/can that get?

Al

Hi Al I don't think your exhaust will get hot enough to melt or deform but
it will be suseptable to cracking from being overheated. Also the shroud
itself probably won't last very long without some airflow to cool it.
Drew





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At 11:01 PM 2/1/2006 -0500, you wrote:

More help needed.I have a 160 HP with crossover exhaust & two mufflers

with heat shrouds.Plan on using both for cabin heat.Going to use a shroud
on the crossover pipe for carb heat.My question is should i take the intake
air for the mufflers from the back off my engine baffels or cut a intake in
the nose bowl.Also the heat boxes i have for cabin heat just lets the heat
from the system dump out under cowling when heat in not on.Should i have
heat boxes with no dumping off hot air when heat is not on.If all this air
is passing over engine & not going down through cylinders just passing
straight out the two 2 " holes in rear baffels will this loss off air
affect cooling off enging.Little confusing i know but would like to do this
correct the first time.

Regards: Alvin
Rebel. 776

Hi Alvin OT to the subject but what are you using for mufflers?
Drew





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As Drew has pointed out you lose the normal heat dissipation that an open
pipe would have by closing it with a complete shroud. Makes it different
temp wise than what's directly around it that's all....and could lead to
premature cracking due to the temp differential. Generally the cabin heat
flappers dump the hot air cowl side if they are not open.... so there is a
continuous air flow thru the shrouds. Also most carb air boxes do this so
when carb heat is not selected the hot air is dumped out the bottom of the
air box to avoid heated air being drawn/forced through the clearances of the
air box even though you don't want carb heat. Speaking of that.....that's
another reason you DON'T want an air inlet hose to the carb heat shroud...ie
no scat hose off the plenum/nose bowl. Just let the engine suck the air from
the shroud with a screened over intake hole. If you have it that way there
would also be less chance of drawing hot air when you don't want it...so if
you are set up that way Al you may be alright on the Carb heat.

Wayne

----- Original Message -----
From: "Drew Dalgleish" <drewjan@cabletv.on.ca>
To: <rebel-builders@dcsol.com>
Sent: Thursday, February 02, 2006 10:21 AM
Subject: Re: Cabin Heat Syatem.

At 07:56 AM 2/2/2006 -0500, you wrote:

Wayne:

You may well be right about ventilation of the carb heat shrout being a
"must", but I don't have it, and have 30+ hours on the airplane without

any

evident problems so far, so I'd like to be sure before changing anything.

How do you know the shrouded area overheats? How hot is too hot? It

seems

to me that on many tightly cowled airplanes they insulate the exhaust to
prevent heat loss to surrounding structure. The carb air shroud is quite

a

ways from anything up the front of an O320/360 in the Murphy

installation,

and it's not going to get any hotter than the exhaust pipe itself

otherwise

would, so I don't think that's a problem. So the problem would have to

be

with the shrouded portion of the exhaust itself, which would have to get

hot

enough to deform, presumably. How hot does/can that get?

Al

Hi Al I don't think your exhaust will get hot enough to melt or deform

but

it will be suseptable to cracking from being overheated. Also the shroud
itself probably won't last very long without some airflow to cool it.
Drew





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