Today's Message Index:
----------------------
1. 06:11 AM - Re: Pumping Losses vs Carb Heat! (Gary Casey)
2. 06:27 AM - Re: Re: Pumping Losses vs Carb Heat! (Vic Jacko)
3. 10:26 AM - Re: Re: Pumping Losses vs Carb Heat! (steve korney)
4. 11:20 AM - Re: Re: Pumping Losses vs Carb Heat! (Vic Jacko)
5. 09:39 PM - Re: Re: Pumping Losses vs Carb Heat! (steve korney)
Message 1
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| Subject: | Re: Pumping Losses vs Carb Heat! |
--> Engines-List message posted by: "Gary Casey" <glcasey@adelphia.net>
<<Climbed to 6,500 feet , leveled off and kept the throttle open all the
way, added
full carb heat, leaned until the engine started to lose power and then
enriched
until it ran smooth. The engine would only pull 2500 RPM in this
configuration.
Thesis: The engine thinks it is flying at a higher altitude than 6,500 feet
due to the hot intake air...Because the carb throttle plate is fully open
there are less pumping
losses than a partially closed throttle.>>
You are precisely right, Vic.
The effects of doing this will be:
1. The inlet air temperature will be higher, increasing the octane
requirement (likelihood of detonation). But the octane requirement of that
engine is very low so I'm sure this would not be a consideration. You are
right in being more cautious on a warm summer day, although at altitude the
manifold pressure is low enough that I wouldn't give this a second thought.
2. The density of the inlet air goes down. This means that you need to run
a higher manifold pressure for a given power output. You've already
compensated for this effect by using rpm as the measure.
3. Higher inlet air temperature will improve vaporization from the
carburetor and hence reduces cylinder-to-cylinder and cycle-to-cycle
air/fuel variation. A very good thing.
4. There will indeed be less pumping loss because there is no pressure drop
across the throttle. This means that the engine will produce slightly more
power at a given manifold pressure and the BSFC will go down (burn less fuel
at a given power setting).
5. The engine will breath unfiltered air, not usually a concern at
altitude.
The only problem I see is that you really don't know how much the
temperature is increased by the carb heat control, although I would guess it
is in the range of 100 degrees.
All in all, there is no reason not to do this under the right conditions
(power settings of 75% or less, no dust, ambient temperatures of maybe 70
degrees or less).
Gary Casey
Message 2
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| Subject: | Re: Pumping Losses vs Carb Heat! |
--> Engines-List message posted by: "Vic Jacko" <vicwj@earthlink.net>
Gary, thanks for your response, you have confirmed my thesis. Now if
someone with a fuel flow device can confirm this we all stand to gain a
little and burn a little less fuel. BTW, many experimnetals use filtered
air right at the carb or throttle body so this may not be an issue.
Perhaps those who are checking this out will "experiment" with different
amounts of carb heat to achieve a balance of the systems.
Vic
----- Original Message -----
From: "Gary Casey" <glcasey@adelphia.net>
Subject: Engines-List: Re: Pumping Losses vs Carb Heat!
> --> Engines-List message posted by: "Gary Casey" <glcasey@adelphia.net>
>
> <<Climbed to 6,500 feet , leveled off and kept the throttle open all the
> way, added
> full carb heat, leaned until the engine started to lose power and then
> enriched
> until it ran smooth. The engine would only pull 2500 RPM in this
> configuration.
>
> Thesis: The engine thinks it is flying at a higher altitude than 6,500
feet
> due to the hot intake air...Because the carb throttle plate is fully open
> there are less pumping
> losses than a partially closed throttle.>>
>
> You are precisely right, Vic.
>
> The effects of doing this will be:
> 1. The inlet air temperature will be higher, increasing the octane
> requirement (likelihood of detonation). But the octane requirement of
that
> engine is very low so I'm sure this would not be a consideration. You are
> right in being more cautious on a warm summer day, although at altitude
the
> manifold pressure is low enough that I wouldn't give this a second
thought.
> 2. The density of the inlet air goes down. This means that you need to
run
> a higher manifold pressure for a given power output. You've already
> compensated for this effect by using rpm as the measure.
> 3. Higher inlet air temperature will improve vaporization from the
> carburetor and hence reduces cylinder-to-cylinder and cycle-to-cycle
> air/fuel variation. A very good thing.
> 4. There will indeed be less pumping loss because there is no pressure
drop
> across the throttle. This means that the engine will produce slightly
more
> power at a given manifold pressure and the BSFC will go down (burn less
fuel
> at a given power setting).
> 5. The engine will breath unfiltered air, not usually a concern at
> altitude.
>
> The only problem I see is that you really don't know how much the
> temperature is increased by the carb heat control, although I would guess
it
> is in the range of 100 degrees.
>
> All in all, there is no reason not to do this under the right conditions
> (power settings of 75% or less, no dust, ambient temperatures of maybe 70
> degrees or less).
>
> Gary Casey
>
>
Message 3
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| Subject: | Re: Pumping Losses vs Carb Heat! |
--> Engines-List message posted by: "steve korney" <s_korney@hotmail.com>
Vic...
Would you explain to me what exactly happens when you go to full carb
heat...What happens to the air flow to heat it up...? Doesn't that relate
to pumping losses...?
Best... Steve
Get ready for school! Find articles, homework help and more in the Back to
Message 4
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| Subject: | Re: Pumping Losses vs Carb Heat! |
--> Engines-List message posted by: "Vic Jacko" <vicwj@earthlink.net>
Steve, I am not an expert on this matter so you are getting my opinion
only: The hot air coming through the carb heat outlet has a higher
density altitude than outside air because it is hotter! The engine thinks
it is at a higher altitude and produces less HP. We must then open the
throttle more to regain the power lost which in effect reduces the pumping
losses and improves efficiency. At the same time we have to lean the
mixture to compensate for the higher density altitude as perceived by the
engine.
The energy to produce the hot air by the carb heat muff is a waste product
of combustion and therefore is free! When you go to full carb heat the
intake air passes over the exhaust system within the carb heat muff and
increases the temperature. This heated air is directed to the intake side
of the throttle body or carb.
That is my story and I am going to stick with it. (no waffling with me)
Vic
----- Original Message -----
From: "steve korney" <s_korney@hotmail.com>
Subject: Re: Engines-List: Re: Pumping Losses vs Carb Heat!
> --> Engines-List message posted by: "steve korney" <s_korney@hotmail.com>
>
> Vic...
>
> Would you explain to me what exactly happens when you go to full carb
> heat...What happens to the air flow to heat it up...? Doesn't that relate
> to pumping losses...?
>
>
> Best... Steve
>
> Get ready for school! Find articles, homework help and more in the Back to
>
>
Message 5
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| Subject: | Re: Pumping Losses vs Carb Heat! |
--> Engines-List message posted by: "steve korney" <s_korney@hotmail.com>
Vic...
Does the heat muff make the air turn or twist or slow down in any way as it
picks up the heat......I think its the same as closing the throttle body a
small amount as far as pumping effeciency goes...
Best... Steve
Get ready for school! Find articles, homework help and more in the Back to
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