Carb Heat Effectiveness

[Alan Hepburn]

I wonder how effective you folks find your carb heat on installations using
the Murphy (Forsling) exhaust system? I am using it with a Vans carb air
box, and it is almost totally ineffective. At runup RPM (~2200) there is no
drop in RPM, and no movement in carb temp. At cruise (~2500), I get maybe a
50 RPM drop.

The muff is like an octagonal can with one side removed. I think things
would work better if I close in most of the opening, forcing the air to
transit the length of the muff, rather than just going around the
circumference and straight in to the scat hose. Any comments?

Al





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[Robert and Olga Johnson]

Hi Al. That was the system I was using on my Rebel with an O320 H2AD. I also
did not get much of a mag drop on run up, but those mornings I was getting
carb ice roughness during taxi, would sure clear up in a hurry when I pulled
the carb heat. I also got about the same drop in cruise as your indicating.
I think the system works quite well. Bob J
----- Original Message -----
From: "Alan Hepburn" <ahepburn@renc.igs.net>
To: <rebel-builders@dcsol.com>
Sent: Friday, July 15, 2005 7:45 AM
Subject: Carb Heat Effectiveness

I wonder how effective you folks find your carb heat on installations using
the Murphy (Forsling) exhaust system? I am using it with a Vans carb air
box, and it is almost totally ineffective. At runup RPM (~2200) there is
no
drop in RPM, and no movement in carb temp. At cruise (~2500), I get maybe
a
50 RPM drop.

The muff is like an octagonal can with one side removed. I think things
would work better if I close in most of the opening, forcing the air to
transit the length of the muff, rather than just going around the
circumference and straight in to the scat hose. Any comments?

Al





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[Bob Patterson]

Hi Al !

I'll second that ! You don't usually see a very big drop with the
Lyc's - not like the 100+ rpm on Continentals, with their cooler
intake air !

Some days it's almost impossible to see the drop at lower rpms,
but never had a problem with clearing ice ...

Have fun flying again ! :-)

.....bobp

-------------------------------orig.-------------------------
On Friday 15 July 2005 10:19 am, Robert and Olga Johnson wrote:

Hi Al. That was the system I was using on my Rebel with an O320 H2AD. I also
did not get much of a mag drop on run up, but those mornings I was getting
carb ice roughness during taxi, would sure clear up in a hurry when I pulled
the carb heat. I also got about the same drop in cruise as your indicating.
I think the system works quite well. Bob J
----- Original Message -----
From: "Alan Hepburn" <ahepburn@renc.igs.net>
To: <rebel-builders@dcsol.com>
Sent: Friday, July 15, 2005 7:45 AM
Subject: Carb Heat Effectiveness

I wonder how effective you folks find your carb heat on installations using
the Murphy (Forsling) exhaust system? I am using it with a Vans carb air
box, and it is almost totally ineffective. At runup RPM (~2200) there is
no
drop in RPM, and no movement in carb temp. At cruise (~2500), I get maybe
a
50 RPM drop.

The muff is like an octagonal can with one side removed. I think things
would work better if I close in most of the opening, forcing the air to
transit the length of the muff, rather than just going around the
circumference and straight in to the scat hose. Any comments?

Al





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[Jean Poirier]

Hello!

I fly a PA-22 Colt (until my Rebel be ready to fly!) with a 0-235 C1B
without oil cooler. My carb heat drop my rpm between 75-100 rpm and also
it is easy too see a temp getting higher on the carb temperature gauge.
No opinion, but just want let you know!

Jean
Rebel 747R
----- Original Message -----
From: "Bob Patterson" <beep@sympatico.ca>
To: <rebel-builders@dcsol.com>
Sent: Friday, July 15, 2005 12:20 PM
Subject: Re: Carb Heat Effectiveness

Hi Al !

I'll second that ! You don't usually see a very big drop with the
Lyc's - not like the 100+ rpm on Continentals, with their cooler
intake air !

Some days it's almost impossible to see the drop at lower rpms,
but never had a problem with clearing ice ...

Have fun flying again ! :-)

.....bobp

-------------------------------orig.-------------------------
On Friday 15 July 2005 10:19 am, Robert and Olga Johnson wrote:

Hi Al. That was the system I was using on my Rebel with an O320 H2AD. I
also
did not get much of a mag drop on run up, but those mornings I was
getting
carb ice roughness during taxi, would sure clear up in a hurry when I
pulled
the carb heat. I also got about the same drop in cruise as your
indicating.
I think the system works quite well. Bob J
----- Original Message -----
From: "Alan Hepburn" <ahepburn@renc.igs.net>
To: <rebel-builders@dcsol.com>
Sent: Friday, July 15, 2005 7:45 AM
Subject: Carb Heat Effectiveness

I wonder how effective you folks find your carb heat on installations
using
the Murphy (Forsling) exhaust system? I am using it with a Vans carb
air
box, and it is almost totally ineffective. At runup RPM (~2200) there
is
no
drop in RPM, and no movement in carb temp. At cruise (~2500), I get
maybe
a
50 RPM drop.

The muff is like an octagonal can with one side removed. I think
things
would work better if I close in most of the opening, forcing the air to
transit the length of the muff, rather than just going around the
circumference and straight in to the scat hose. Any comments?

Al





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[Drew Dalgleish]

Hi Al One of the tricks I learned from one of the Tony Bingelis books is
to wrap a streched door spring around the exhaust pipe. The spring radiates
a lot of extra heat into the carb air.

At 07:45 AM 7/15/2005 -0400, you wrote:

I wonder how effective you folks find your carb heat on installations using
the Murphy (Forsling) exhaust system? I am using it with a Vans carb air
box, and it is almost totally ineffective. At runup RPM (~2200) there is no
drop in RPM, and no movement in carb temp. At cruise (~2500), I get maybe a
50 RPM drop.

The muff is like an octagonal can with one side removed. I think things
would work better if I close in most of the opening, forcing the air to
transit the length of the muff, rather than just going around the
circumference and straight in to the scat hose. Any comments?

Al





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Drew





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[Wayne G. O'Shea]

You receive that engine yet Jean?? Wayne

----- Original Message -----
From: "Jean Poirier" <oxyport@globetrotter.net>
To: <rebel-builders@dcsol.com>
Sent: Friday, July 15, 2005 1:21 PM
Subject: Re: Carb Heat Effectiveness

Hello!

I fly a PA-22 Colt (until my Rebel be ready to fly!) with a 0-235 C1B
without oil cooler. My carb heat drop my rpm between 75-100 rpm and also
it is easy too see a temp getting higher on the carb temperature gauge.
No opinion, but just want let you know!

Jean
Rebel 747R
----- Original Message -----
From: "Bob Patterson" <beep@sympatico.ca>
To: <rebel-builders@dcsol.com>
Sent: Friday, July 15, 2005 12:20 PM
Subject: Re: Carb Heat Effectiveness

Hi Al !

I'll second that ! You don't usually see a very big drop with the
Lyc's - not like the 100+ rpm on Continentals, with their cooler
intake air !

Some days it's almost impossible to see the drop at lower rpms,
but never had a problem with clearing ice ...

Have fun flying again ! :-)

.....bobp

-------------------------------orig.-------------------------
On Friday 15 July 2005 10:19 am, Robert and Olga Johnson wrote:

Hi Al. That was the system I was using on my Rebel with an O320 H2AD. I
also
did not get much of a mag drop on run up, but those mornings I was
getting
carb ice roughness during taxi, would sure clear up in a hurry when I
pulled
the carb heat. I also got about the same drop in cruise as your
indicating.
I think the system works quite well. Bob J
----- Original Message -----
From: "Alan Hepburn" <ahepburn@renc.igs.net>
To: <rebel-builders@dcsol.com>
Sent: Friday, July 15, 2005 7:45 AM
Subject: Carb Heat Effectiveness

there

to

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[Jean Poirier]

Hello Wayne

Yes I have received my engine. Look good but I will only know when I will
put it in service! There is no output for vacuum pump and no quick drain
on oil pan. I will probably just fit a vacuum horn on the left side of the
airplane but for the quick drain, do you just tap a pipe tread hole in the
pan? (this idea look not really good) or I have to forget about it?

Jean
Rebel 747R
----- Original Message -----
From: "Wayne G. O'Shea" <oifa@irishfield.on.ca>
To: <rebel-builders@dcsol.com>
Sent: Monday, July 25, 2005 3:42 PM
Subject: Re: Carb Heat Effectiveness

You receive that engine yet Jean?? Wayne

----- Original Message -----
From: "Jean Poirier" <oxyport@globetrotter.net>
To: <rebel-builders@dcsol.com>
Sent: Friday, July 15, 2005 1:21 PM
Subject: Re: Carb Heat Effectiveness

Hello!

I fly a PA-22 Colt (until my Rebel be ready to fly!) with a 0-235 C1B
without oil cooler. My carb heat drop my rpm between 75-100 rpm and
also
it is easy too see a temp getting higher on the carb temperature gauge.
No opinion, but just want let you know!

Jean
Rebel 747R
----- Original Message -----
From: "Bob Patterson" <beep@sympatico.ca>
To: <rebel-builders@dcsol.com>
Sent: Friday, July 15, 2005 12:20 PM
Subject: Re: Carb Heat Effectiveness

Hi Al !

I'll second that ! You don't usually see a very big drop with
the
Lyc's - not like the 100+ rpm on Continentals, with their cooler
intake air !

Some days it's almost impossible to see the drop at lower rpms,
but never had a problem with clearing ice ...

Have fun flying again ! :-)

.....bobp

-------------------------------orig.-------------------------
On Friday 15 July 2005 10:19 am, Robert and Olga Johnson wrote:

there

to

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[Alan Hepburn]

I find the carb heat on my O-360 almost totally ineffective. With the
cooler weather coming on, I'd like to do something about that. I am
using the standard Murphy (Forsling) exhaust and muffs, with the Vans
airbox. I have a carb heat probe, and if I see 1*C difference, and a
few 10s of RPM change, that's about it. Talked to Forsling at OSH and
he said to orient the slot in the muff so it was facing the other
exhaust pipe. That would require reworking the outlet position on my
muff, which would be OK if I was satisfied it would work.

I wonder what others are getting?

Al




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[Wayne G. O'Shea]

I get a 150 to 200 RPM drop on my O-320-C2A at 1800 RPM's. I'm using nothing
but an old small shroud from some certified aircraft that covers no more
than about 3 inches of a single pipe.

Does your engine need to be leaned agressively to get a higher RPM. Maybe
you are already running so rich the heated air from carb heat doesn't have
the same effect....but of course that doesn't explain the temp difference.
Sure you don't have a blocked/collapsed SCAT tube from the shroud to the
carb box....or a flapper valve that isn't cycling all the way to draw air
strictly from the shroud.

Wayne

----- Original Message -----
From: "Alan Hepburn" <ahepburn@renc.igs.net>
To: <rebel-builders@dcsol.com>
Sent: Tuesday, September 13, 2005 11:20 PM
Subject: Carb Heat Effectiveness

I find the carb heat on my O-360 almost totally ineffective. With the
cooler weather coming on, I'd like to do something about that. I am
using the standard Murphy (Forsling) exhaust and muffs, with the Vans
airbox. I have a carb heat probe, and if I see 1*C difference, and a
few 10s of RPM change, that's about it. Talked to Forsling at OSH and
he said to orient the slot in the muff so it was facing the other
exhaust pipe. That would require reworking the outlet position on my
muff, which would be OK if I was satisfied it would work.

I wonder what others are getting?

Al




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[Walter Klatt]

I get about 100 rpm drop at cruise power with carb heat. It's
saved me twice now. I just have a single shroud on one of my
cross-over pipes, which is open at each end.

Walter

-----Original Message-----
From: mike.davis@dcsol.com
[mailto:mike.davis@dcsol.com]On Behalf Of
Wayne G. O'Shea
Sent: Tuesday, September 13, 2005 8:26 PM
To: rebel-builders@dcsol.com
Subject: Re: Carb Heat Effectiveness


I get a 150 to 200 RPM drop on my O-320-C2A at 1800
RPM's. I'm using nothing
but an old small shroud from some certified aircraft
that covers no more
than about 3 inches of a single pipe.

Does your engine need to be leaned agressively to get
a higher RPM. Maybe
you are already running so rich the heated air from
carb heat doesn't have
the same effect....but of course that doesn't explain
the temp difference.
Sure you don't have a blocked/collapsed SCAT tube from
the shroud to the
carb box....or a flapper valve that isn't cycling all
the way to draw air
strictly from the shroud.

Wayne

----- Original Message -----
From: "Alan Hepburn" <ahepburn@renc.igs.net>
To: <rebel-builders@dcsol.com>
Sent: Tuesday, September 13, 2005 11:20 PM
Subject: Carb Heat Effectiveness

I find the carb heat on my O-360 almost totally

ineffective. With the

cooler weather coming on, I'd like to do something

about that. I am

using the standard Murphy (Forsling) exhaust and

muffs, with the Vans

airbox. I have a carb heat probe, and if I see 1*C

difference, and a

few 10s of RPM change, that's about it. Talked to

Forsling at OSH and

he said to orient the slot in the muff so it was

facing the other

exhaust pipe. That would require reworking the

outlet position on my

muff, which would be OK if I was satisfied it would work.

I wonder what others are getting?

Al

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[Robert and Olga Johnson]

Allan; I did not see much of an RPM change on my O320 H2AD (160HP) with carb
heat pulled either. I do know that if I got a roughness in the engine at any
time taxiing or flying, pulling carb heat fixed the problem. This was with
the Murphy standard Firewall forward package, exhaust and open carb heat
muff. Bob J ( formerly Rebel 652)
----- Original Message -----
From: "Alan Hepburn" <ahepburn@renc.igs.net>
To: <rebel-builders@dcsol.com>
Sent: Tuesday, September 13, 2005 11:20 PM
Subject: Carb Heat Effectiveness

I find the carb heat on my O-360 almost totally ineffective. With the
cooler weather coming on, I'd like to do something about that. I am
using the standard Murphy (Forsling) exhaust and muffs, with the Vans
airbox. I have a carb heat probe, and if I see 1*C difference, and a
few 10s of RPM change, that's about it. Talked to Forsling at OSH and
he said to orient the slot in the muff so it was facing the other
exhaust pipe. That would require reworking the outlet position on my
muff, which would be OK if I was satisfied it would work.

I wonder what others are getting?

Al




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[Ralph Baker]

Alan,
As you know I am also using the Van's airbox on our O-360. We haven't
flown but I have looked at the Van's heated air inlet into the box and
wondered how effective it would be with the standoff mount. For others
- the hot air scat tube enters the flat side of a raised channel over
the box intake. This is to allow heated air an escape route when the
airbox intake is closed. Van's uses a positive pressure from the cowl
front so heated air must escape continuously. The Forsling muff depends
on intake vacuum to pull air over the exhaust for heating and does not
require continuous heat disposal.

My solution, if needed, would be to progressively block the open sides
of the standoff until sufficient tach drop was noted or heat rise
measured. At present I believe that unheated air is being drawn in for
combustion at that is the path of least resistance. The intake
restriction might result in a slight max power reduction but better that
than 100% reduction.
Ralph Baker



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[Alan Hepburn]

Ralph:

I modified the Vans design so there is no significant spillage path. The
Forsling outlet is at one end of the muff, and I was thinking of blocking
off some of the open side to force the air to take a longer path along the
exhaust tube. Wayne: it's kind of difficult to see what's happening to the
flapper which would be under dynamic air pressure at cruise - not an easy
place to observe! Maybe the carb heat cable is simply bending. I'll have
to think about how to stiffen it up, Maybe some Viagra in the gas!

Al





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[Ralph Baker]

Alan,
(And others using Van's airbox) Vans uses ball/spring detent Bowden
cables to prevent creep on the carb heat cable. You might want to try
carb heat at full throttle after measuring control knob extension to see
if there is any creep.
Ralph Baker



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