Craig,
The cfm figures for carbs are calculated @ around 1.5" Hg as this is the
approximate pressure differential across the carb @ Wide Open Throttle?. As
you pointed out if this constant is used, it makes a convenient basis for
comparison of flow rates
Cheers
----------
From: Craig Overend <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Subject: Re: Airflow calculations
Date: Thursday, September 14, 2000 2:01
Terry,
My understanding is that for any fluid(air) to move from one point to
another there must be a force acting on it. This can be a pressure
difference or gravity for example.
To calculate volumetric flow rate you need to measure the pressure
difference across a known calibrated orifice.
To compare airflow CFM readings you need to know at what pressure
difference(airspeed) it was measured at. For example 100CFM@10"
Water(.3613963 PSI) is NOT the same as 100CFM@20" Water. If you were to
convert the 20"water to
10"water so you could then directly compare them and you'd get lower
than 100CFM after conversion.
Holley use a strange test pressure something like 1.5" of mercury, I
cant remember exactly.
So unless the pressure difference is known CFM ratings alone are
useless.
Craig.
> Terry & Heather wrote:
>
> Kevin,
>
> very interesting post.
>
> I have just one question - carbies are rated at a certain cfm eg
> Holley 780 cfm (from my Ford 351 days)
>
> How do you calculate the cfm rating of a carbie, sort of like a pipe I
> guess which is along the lines of the original question.
>
> What's the cfm rating of a DCOE45?
>
> Terry
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]]On Behalf Of
> Kevin
> Sent: Thursday, 7 September 2000 10:33 AM
> To: [EMAIL PROTECTED]
> Subject: Airflow calculations
>
> This is the formula we use at work to work out air flow
> needs
>
> Air flow (CFM) = Displacement (cubic inch) X RPM X VE
> 1728 CF
>
> CYCLE FACTOR (CF)
> CF: 4 cycle diesel/petrol engine = 2
> CF: 2 " " " " = 1
>
> VOLUMETRIC EFFICIENCY (VE)
> Naturally aspirated diesel/petrol engine = 0.85
> Supercharged engine = 1.2
> Turbo engine (we use this on for diesels) = 1.4
>
> Eg Airflow = 109 x 6000 X 0.85
> 1728 2
>
> = 555900
> 3456
>
> = 160.85 cfm (this suits a 1800cc engine)
>
> Litres to CI
>
> 1 LT = 60.5 CI eg 1.8 lt X 60.5 = 108.9 CI
>
> >>>>
>
> <?fontfamily><?param
> Tahoma><?smaller>-----Original
> Message-----
> From:
> [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]]On
> Behalf Of brad
> Sent: Wednesday, 6 September 2000 12:57
> PM
> To: [EMAIL PROTECTED]
> Subject: airflow calculations
>
> <?/smaller><?/fontfamily><?fontfamily><?param
> Arial><?smaller>does any 1 know the
> formula for calculating the cfm of a
> pipe
> <?/smaller><?/fontfamily>
> <?fontfamily><?param
> Arial><?smaller>thanx in advance
> <?/smaller><?/fontfamily><?fontfamily><?param
> Arial><?smaller>Brad
> <?/smaller><?/fontfamily>
>
> ---------------------------------------------------
> Kevin Harlan
> WILDKAT SPARES
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>
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