X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 15 May 2006 19:02:23 -0400 Message-ID: X-Original-Return-Path: Received: from pop-savannah.atl.sa.earthlink.net ([207.69.195.69] verified) by logan.com (CommuniGate Pro SMTP 5.0.9) with ESMTP id 1114780 for lml@lancaironline.net; Mon, 15 May 2006 18:55:56 -0400 Received-SPF: none receiver=logan.com; client-ip=207.69.195.69; envelope-from=douglasbrunner@earthlink.net Received: from h-66-167-148-102.mclnva23.dynamic.covad.net ([66.167.148.102] helo=DFWK3391) by pop-savannah.atl.sa.earthlink.net with smtp (Exim 3.36 #10) id 1Ffly3-0002iG-00 for lml@lancaironline.net; Mon, 15 May 2006 18:55:11 -0400 X-Original-Message-ID: <002f01c67872$9e58ea70$210110ac@DFWK3391> From: "Douglas Brunner" X-Original-To: "Lancair Mailing List" References: Subject: Re: [LML] Re: Positive Crankcase Vacuum X-Original-Date: Mon, 15 May 2006 18:55:10 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_002C_01C67851.172124D0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2869 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2869 This is a multi-part message in MIME format. ------=_NextPart_000_002C_01C67851.172124D0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Thanks for the comments. I hope to be able to judge for myself the increase in horsepower on a = dyno. Mike Moore of AvWorks has extended to me the offer of being able to run my engine (under close supervision) on a dyno = after it is built. I am looking forward to this for many reasons, not the least of which is being able to see exactly how much horsepower = I am getting. The other benefits you mention are nice as well and you forgot to = mention how nice and clean the belly of my plane will look. D. Brunner ----- Original Message -----=20 From: REHBINC@aol.com=20 To: Lancair Mailing List=20 Sent: Monday, May 15, 2006 5:06 PM Subject: [LML] Re: Positive Crankcase Vacuum Doug, I'm not sure how much benefit in reduced windage losses you would get = from applying a vacuum to the crank case. The biggest areas for gain = here are in oil pan design, windage trays and crank scrapers that work = to screen the oil droplets from the air down into the sump and protect = the oil surface from the 'wind' in the crankcase. Yes, this can make a = substantial difference in a race engine, but as Paul said at 2700 rpm = it's questionable just how much power could be recovered from windage = reduction. There are two benefits from crank case vacuum that you haven't = mentioned. The first is reduced dilution of the fuel air charge in the = cylinder and its effect on power. During the intake stroke, cylinder = pressure is well below atmospheric (naturally aspirated) so ring leakage = flows into the cylinder. With crank case vacuum, the ring leakage flow = is reduced and at times even reversed. There are three effects as a = result: First, the area between the top ring land and the cylinder is = full of exhaust products, partially burned fuel and raw fuel all of = which are detrimental to the power stroke. During the intake and = compression stroke, some of these products are swept into the combustion = chamber where they reduce power. Crank case vacuum helps to remove them = from the cylinder. Second, the air leaking from the crankase is fuel = lean and its addition to the cylinder is also detrimental to power. = Third=20 ring leakage into the cylinder carries with it a small amoint of oil. = This also displaces fuel air mixture and reduces power, but more = importantly oil has a very low octane rating and contributes to = detonation. The second benefit is improved oil life. Unburned fuel and exhaust = gasses are continually leaking from the cylinder during the combustion, = exhaust and compression strokes and contaminating the oil. The oil = contains various additives to prevent damage to the engine as a result = of contamination with these chemicals. As contamination increases, the = additives are expended and protection is lost. Crankase vacuum helps to = volitize some of the compounds and draw them out of the oil and into the = exhaust. This was a beneifcial consequence of the positive crankcase = ventilation (PCV) system on cars in the early '70's. While the vacuum = generated in the crankcase was slight, the system scavenged vapors from = the crankcase and greatly reduced contamination of the oil. This = resulted in extended oil changes intervals from 3 thousand miles in the = '60's to 4 or 5 thousand in the '70's. Of course today, thousands of = people throw perfectly good oil away every 3000 miles anyway. Old habits = die hard. Rob ------=_NextPart_000_002C_01C67851.172124D0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Thanks for the comments.
 
I hope to be able to judge for myself the increase in horsepower on = a=20 dyno.  Mike Moore of AvWorks has extended to me the
offer of being able to run my engine (under close supervision) on a = dyno=20 after it is built.  I am looking forward to this for many = reasons,
not=20 the least of which is being able to see exactly how much horsepower I am = getting.
 
The other benefits you mention are nice as well and you forgot to = mention=20 how nice and clean the belly of my plane will look.
 
D. Brunner
----- Original Message -----
From:=20 REHBINC@aol.com=20
Sent: Monday, May 15, 2006 5:06 = PM
Subject: [LML] Re: Positive = Crankcase=20 Vacuum

Doug,
 
I'm not sure how much benefit in reduced windage losses you would = get=20 from applying a vacuum to the crank case. The biggest areas for gain = here are=20 in oil pan design, windage trays and crank scrapers that work to = screen the=20 oil droplets from the air down into the sump and protect the oil = surface from=20 the 'wind' in the crankcase. Yes, this can make a substantial = difference in a=20 race engine, but as Paul said at 2700 rpm it's questionable just how = much=20 power could be recovered from windage reduction.
 
There are two benefits from crank case vacuum that you haven't = mentioned.=20 The first is  reduced dilution of the fuel air charge in the = cylinder and=20 its effect on power. During the intake stroke, cylinder pressure is = well below=20 atmospheric (naturally aspirated) so ring leakage flows into the = cylinder.=20 With crank case vacuum, the ring leakage flow is reduced and at = times=20 even reversed. There are three effects as a result: First, the area = between=20 the top ring land and the cylinder is full of exhaust products, = partially=20 burned fuel and raw fuel all of which are detrimental to the = power=20 stroke. During the intake and compression stroke, some of these = products are=20 swept into the combustion chamber where they reduce power. Crank = case=20 vacuum helps to remove them from the cylinder. Second, the air = leaking=20 from the crankase is fuel lean and its addition to the cylinder is = also=20 detrimental to power. Third 
ring leakage into the cylinder carries with it a small amoint of = oil.=20 This also displaces fuel air mixture and reduces power, but more = importantly=20 oil has a very low octane rating and contributes to = detonation.
 
The second benefit is improved oil life. Unburned fuel and = exhaust gasses=20 are continually leaking from the cylinder during the combustion, = exhaust and=20 compression strokes and contaminating the oil. The oil contains = various=20 additives to prevent damage to the engine as a result of contamination = with=20 these chemicals. As contamination increases, the additives are = expended and=20 protection is lost. Crankase vacuum helps to volitize some of the = compounds=20 and draw them out of the oil and into the exhaust. This was a = beneifcial=20 consequence of the positive crankcase ventilation (PCV) system on = cars in=20 the early '70's. While the vacuum generated in the crankcase was = slight, the=20 system scavenged vapors from the crankcase and greatly reduced = contamination=20 of the oil. This resulted in extended oil changes intervals from 3=20 thousand miles in the '60's to 4 or 5 thousand in the '70's. = Of=20 course today, thousands of people throw perfectly good oil away every = 3000=20 miles anyway. Old habits die hard.
 
Rob
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