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Subaru Specific Fuel Consumption

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Subaru Specific Fuel Consumption

Posted: Fri Feb 17, 2012 8:39 pm
by Mike Davis
One more question answered... here is the response from Crossflow about the
SFC numbers for their engines. Thought I'd add one thing to the information
below... here are the peak HP ratings for these engines:

CF4-33 - 250 (normally aspirated @ 5650 rpm)
CF4-33T - 300 (turbo @ 5600 rpm)
CF4-33THO - 320 (high output turbo @ 6050 rpm)
Mike,

All our figures are metered at 75% engine load, and may vary slightly
according to atmospheric conditions. CF4-33(9.5gph@75%),
CF4-33T(10.5@75%),
CF4-33THO(11.5GPH@75%). I was not aware of the typo. Thanks, I will
correct
it.

Jorge
So the SFC at 75% is about:

CF4-33 - .050666
CF4-33T - .046666
CF4-33THO - .047916

Mike

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Subaru Specific Fuel Consumption

Posted: Fri Feb 17, 2012 8:40 pm
by klehman
Mike
If we define sfc as lb. fuel per hp. hr the numbers seem way off or are
you using different units? Even if we use the imperial gal subterfuge
(about 25% larger than US gal) the CF4-33 is using at most (I think)
about 65 lb to make 187 hp or .35 sfc which would be impressive. Using
US gal, the numbers would be kind of hard to believe based on what I
know about engines and thermodynamics.
Ken



Mike Davis wrote:
One more question answered... here is the response from Crossflow about the
SFC numbers for their engines. Thought I'd add one thing to the information
below... here are the peak HP ratings for these engines:

CF4-33 - 250 (normally aspirated @ 5650 rpm)
CF4-33T - 300 (turbo @ 5600 rpm)
CF4-33THO - 320 (high output turbo @ 6050 rpm)
Mike,

All our figures are metered at 75% engine load, and may vary slightly
according to atmospheric conditions. CF4-33(9.5gph@75%),
CF4-33T(10.5@75%),
CF4-33THO(11.5GPH@75%). I was not aware of the typo. Thanks, I will
correct
it.

Jorge
So the SFC at 75% is about:

CF4-33 - .050666
CF4-33T - .046666
CF4-33THO - .047916
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Subaru Specific Fuel Consumption

Posted: Fri Feb 17, 2012 8:40 pm
by Mike Davis
I must have done something wrong... but I intended to calculate lbs of fuel
per hp per hour... let me try it again, and you can check my work.

For the CF4-33T
75% of 300 hp is 225 hp
And we are using 10.5 gal of fuel in one hour at that setting.
Assuming 1 gallon of premium auto gas weighs 6.17 lbs, times 10.5 gal hour,
that's 64.785 lbs per hour, divided by 225...
so the sfc is 0.2879333333333 lbs of fuel per hp per hour. WOW!

You know... looking at that, I have no idea how I came up with those other
numbers! I've tried it several different ways, and I sure can't seem to do
it again. :-)

Thanks for calling me on it... I like these numbers a lot better!

Mike


----- Original Message -----
From: <klehman@albedo.net>
To: " (Murphy Rebel Builders List)" <murphy-rebel@dcsol.com>
Sent: Wednesday, January 24, 2001 4:28 PM
Subject: Re: Subaru Specific Fuel Consumption

Mike
If we define sfc as lb. fuel per hp. hr the numbers seem way off or are
you using different units? Even if we use the imperial gal subterfuge
(about 25% larger than US gal) the CF4-33 is using at most (I think)
about 65 lb to make 187 hp or .35 sfc which would be impressive. Using
US gal, the numbers would be kind of hard to believe based on what I
know about engines and thermodynamics.
Ken



Mike Davis wrote:
One more question answered... here is the response from Crossflow about
the
SFC numbers for their engines. Thought I'd add one thing to the
information
below... here are the peak HP ratings for these engines:

CF4-33 - 250 (normally aspirated @ 5650 rpm)
CF4-33T - 300 (turbo @ 5600 rpm)
CF4-33THO - 320 (high output turbo @ 6050 rpm)
Mike,

All our figures are metered at 75% engine load, and may vary slightly
according to atmospheric conditions. CF4-33(9.5gph@75%),
CF4-33T(10.5@75%),
CF4-33THO(11.5GPH@75%). I was not aware of the typo. Thanks, I will
correct
it.

Jorge
So the SFC at 75% is about:

CF4-33 - .050666
CF4-33T - .046666
CF4-33THO - .047916
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Subaru Specific Fuel Consumption

Posted: Fri Feb 17, 2012 8:40 pm
by klehman
Hi Mike

The math looks OK now. I still recommend you ignore the number though
and plan on maybe 25% less burn than a Lycoming, as Crossflow also seems
to be reporting from user experience. The 3.3 is essentially a 2.2 with
two extra cylinders so you should also be able to somewhat extrapolate
the burns from the guys here that are using the 2.2. Not sure what you
are planning, but I did reduce my fuel tank size to 5 bays instead of 6
for the ej22 in a standard Rebel.

Ken


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