X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 15 Dec 2005 12:30:29 -0500 Message-ID: X-Original-Return-Path: Received: from wind.imbris.com ([216.18.130.7] verified) by logan.com (CommuniGate Pro SMTP 5.0.4) with ESMTPS id 883326 for lml@lancaironline.net; Thu, 15 Dec 2005 11:01:51 -0500 Received-SPF: none receiver=logan.com; client-ip=216.18.130.7; envelope-from=brent@regandesigns.com Received: from [192.168.1.100] (vsat-148-63-101-227.c002.t7.mrt.starband.net [148.63.101.227]) (authenticated bits=0) by wind.imbris.com (8.12.11/8.12.11.S) with ESMTP id jBFG0pRR091304 for ; Thu, 15 Dec 2005 08:00:56 -0800 (PST) (envelope-from brent@regandesigns.com) X-Original-Message-ID: <43A1932B.4050101@regandesigns.com> X-Original-Date: Thu, 15 Dec 2005 08:00:43 -0800 From: Brent Regan User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax) X-Accept-Language: en-us, en MIME-Version: 1.0 X-Original-To: Lancair Subject: Re: SCFM Content-Type: multipart/alternative; boundary="------------030409070501000603010409" This is a multi-part message in MIME format. --------------030409070501000603010409 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Reposted to add to the confusion. Brent -------- Original Message -------- Subject: Re: SCFM Date: Sun, 21 Mar 2004 17:09:30 -0800 From: Brent Regan To: Lancair Art asks: <<<< Question for Brent Regan Brent Can you give me the formula's to figure CFM required for a TSIO 550 and SCFM rating for a K & N filter? >>>> Calculating the Standard Cubic Foot per Minute (SCFM) is, at best, an approximation. The basic strategy is to take the displacement of the engine (550 cubic inches in the case of the Continental) and multiply it how many "displacements" the engine uses in a minute to get the volumetric needs of the engine. Remember that in a 4 stroke engine it takes two revolutions to get one displacement so divide the RPM by two and multiply by RPM to get the (theoretical) cubic inch per minute flow through the engine. Divide this by 1,728 (cubic inches per cubic foot) to get Cubic Feet per Minute (CFM). This assumes the engine has no net restriction on airflow. There are a lot of things that effect the air flow throughout the engine. Well designed "tuned" intake and exhaust runners improve flow. So do superchargers (this includes turbochargers) and a well designed cam. Filters, bends, friction, valves and throttle plates all reduce flow. The net effect of all these factors is defined at the Volumetric Efficiency, which is the ratio of the actual flow versus the theoretical flow. Altitude and temperature have an effect as related to standard atmospheric conditions. The wide open throttle (WOT) volumetric efficiency varies with the engine and installation but a conservative (and easy) figure to use for a naturally aspirated engine is 1.0 and a turbocharged engine is 1.1. The volumetric efficiency of my TIO-540 at 350 Hp is 1.043. I know this because I measured it on a calibrated dynamometer. The airflow requirement of the TSIO-550 would therefore be 275 cuin/revolution x 2700 RPM /1728 cuin/cuft x 1.10 = 472 CFM. The density of air at standard conditions is 0.07647 Lb/cuft. The mass flow requirements of the engine at WOT and standard conditions is therefore 472 CFM x 0.07647 Lb/CFM = 36 pounds per minute. For a given power setting the mass flow through the engine must remain the same. For a turbocharged engine at a fixed power output the CFM flow through the filter increases with altitude because the density of the air is decreasing. For the same TSIO-550 at 75% power you need about 27 pounds of air per minute to feed the fire. At FL250 every cubic foot contains 0.0343 lbs of air so you need to flow about 780 CFM through the filter. The air pressure at FL250 is about 150 inches of water. A dirty 400 SCFM filter may cost you 8 inches of water or better than 5% power. Filter flow ratings are available from the manufacturer. Be sure you get the pressure drop across the filter at rated flow so you can do an accurate comparison between filters. Regards Brent Regan --------------030409070501000603010409 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit Reposted to add to the confusion.
Brent

-------- Original Message --------
Subject: Re: SCFM
Date: Sun, 21 Mar 2004 17:09:30 -0800
From: Brent Regan <brent@regandesigns.com>
To: Lancair <lml@lancaironline.net>


Art asks:

<<<<
Question for Brent Regan
Brent
Can you give me the formula's to figure CFM required
for a TSIO 550 and SCFM rating for a K & N filter?
>>>>

Calculating the Standard Cubic Foot per Minute (SCFM) is, at best, an approximation. The basic strategy is to take the displacement of the engine (550 cubic inches in the case of the Continental) and multiply it how many "displacements" the engine uses in a minute to get the volumetric needs of the engine. Remember that in a 4 stroke engine it takes two revolutions to get one displacement so divide the RPM by two and multiply by RPM to get the (theoretical) cubic inch per minute flow through the engine.  Divide this by 1,728 (cubic inches per cubic foot) to get  Cubic Feet per Minute (CFM).  This assumes the engine has no net restriction on airflow.  There are a lot of things that effect  the air flow throughout the engine.  Well designed "tuned" intake and exhaust runners improve flow. So do superchargers (this includes turbochargers) and a well designed cam. Filters, bends, friction, valves and throttle plates all reduce flow. The net effect of all  these factors is defined at the Volumetric Efficiency, which is the ratio of the actual flow versus the theoretical flow. Altitude and temperature have an effect as related to standard atmospheric conditions.

The wide open throttle (WOT) volumetric efficiency varies with the engine and installation but a conservative (and easy) figure to use for a naturally aspirated engine is 1.0 and a turbocharged engine is 1.1.  The volumetric efficiency of my TIO-540 at 350 Hp is 1.043. I know this because I measured it on a calibrated dynamometer.

The airflow requirement of the TSIO-550 would therefore be 275 cuin/revolution x 2700 RPM /1728 cuin/cuft x 1.10 = 472 CFM. The density of air at standard conditions is 0.07647 Lb/cuft. The mass flow requirements of the engine at WOT and  standard conditions is therefore 472 CFM x 0.07647 Lb/CFM = 36 pounds per minute. For a given power setting the mass flow through the engine must remain the same. For a turbocharged engine at a fixed power output the CFM flow through the filter increases with altitude because the density of the air is decreasing.

For the same TSIO-550 at 75% power you need about 27 pounds of air per minute to feed the fire. At FL250 every cubic foot contains 0.0343 lbs of air so you need to flow about 780 CFM through the filter. The air pressure at FL250 is about 150 inches of water.  A dirty 400 SCFM filter may cost you 8 inches of water or better than 5% power.

Filter flow ratings are available from the manufacturer. Be sure you get the pressure drop across the filter at rated flow so you can do an accurate comparison between filters.

Regards
Brent Regan



 
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