X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 16 Nov 2010 09:24:53 -0500 Message-ID: X-Original-Return-Path: Received: from web57514.mail.re1.yahoo.com ([66.196.100.81] verified) by logan.com (CommuniGate Pro SMTP 5.3.10) with SMTP id 4580830 for lml@lancaironline.net; Tue, 16 Nov 2010 08:26:46 -0500 Received-SPF: none receiver=logan.com; client-ip=66.196.100.81; envelope-from=casey.gary@yahoo.com Received: (qmail 47370 invoked by uid 60001); 16 Nov 2010 13:26:09 -0000 DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=Cn3SZy652A7fXczEnsQiskqjjCDCXYc9EGQKlfnX8lixbVDekjKddviqnnAlsS5/ZyFJhLKKCREXRwPXZPbciBULyBmBE4kX1mB76Q0bEdhgh4ck6kpWsIbubh20FQRadW+BUyAkXkO1NDiKDIgM1RXzf4EpVunuK7QhgkacwhM=; X-Original-Message-ID: <296439.47155.qm@web57514.mail.re1.yahoo.com> X-YMail-OSG: lbIZqKoVM1mLScwqy1E1dRo52LQZ7chBCpYYIhUFN_.T.84 ekXbOPKJoXWPKb9NsC3iRZIP6LPc0B5MjXQ3CT1_l.eUB.zaRX9iZdRFoVRQ vD_Np3Vg3chENNqEzCPuconVz7kyrxwcKHdmIR7_Crrvs3qX6h71er3uqdsj 5oWais9JEcBhZ5qcP9WqAy1WN0B6fywldf5tR700YNpp0k0JmW_n3IhJrRKc yPjSQhqShScuHl513iM9p8XoauvN3I4tCikKidDmjwy95EMSNCQLBtr.hl.U X Received: from [97.122.152.1] by web57514.mail.re1.yahoo.com via HTTP; Tue, 16 Nov 2010 05:26:08 PST X-Mailer: YahooMailRC/504.5 YahooMailWebService/0.8.107.285259 References: X-Original-Date: Tue, 16 Nov 2010 05:26:08 -0800 (PST) From: Gary Casey Subject: Re: Electronic Ignition X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-630661635-1289913968=:47155" --0-630661635-1289913968=:47155 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable I certainly agree with the statements below from Mr. Brunner. A few reinfo= rcing =0Acomments:=0ABack in the old days when everyone flew at 8,000 feet = or less, the mag with its =0Afixed timing worked quite well. At takeoff th= e mixture was so rich that =0Acombustion slowed and the peak cylinder press= ure could end up at 16 degrees ATC, =0Aas suggested below. When at a cruis= ing altitude the mixture was leaned, =0Aprobably to about peak EGT (carbure= ted systems) and that sped up the combustion =0Aso that even with the lower= manifold pressure the peak pressure was still near =0A16 ATC. Then we sta= rted to fly above 10,000 feet and wanted to go LOP. Lower =0Amanifold pres= sures slow the combustion as does LOP mixtures. Now the spark was =0Adefin= itely retarded from optimum. The solution? An ignition system that =0Aadv= ances the timing as the manifold pressure drops. But that still doesn't = =0Acompensate for LOP operation - the Prism system will do that.=0A=0AAnd, = yes, the electronic system only increases power when it advances timing =0A= over the fixed mag AND the peak cylinder pressure occurs after 16 ATC. Whe= n is =0Athat? Probably at any mixture when flying at significantly over 10= ,000 feet =0A(manifold pressures less than 20). And especially when at low= manifold =0Apressures AND running LOP. So, in my opinion the advantage is= real when typical =0Acruising is done over 10,000 and LOP. Otherwise the = benefits are not all that =0Apersuasive. What about turbocharged engines? = How often are they operated at =0Aless than 20 inches? The only problem I= see with mags (on turbocharged engines) =0Ais potential for cross-firing w= ithin the distributor cap, eliminated by most =0Aelectronic systems. TBO? = Certainly any time the peak cylinder pressure is =0Aincreased TBO is reduc= ed. But I think a 10:1 engine operated like it was =0Aturbocharged (avoid = peak EGT like the plague) could last as long as a standard =0Aengine operat= ed more casually. And the lower EGT produced by the higher =0Acompression = is likely to increase exhaust valve life.=0AGary Casey=0AES N224SG, IO-540,= 10:1, single Lightspeed, always cruising at 12,000+, LOP=0A=0AAt the risk = of starting a =E2=80=9Ctheological=E2=80=9D controversy, I would like to ra= ise some =0Areservations about electronic ignition systems (other than reli= ability and loss =0Aof electrical power)=0A =0APeak intracylinder pressure = (the point in the combustion cycle at which pressure =0Ain the cylinder is = highest =3D effective timing) is related to 3 things; spark =0Atiming, rpm = and MIXTURE. =0A =0AWhy mixture? Because air and fuel mixtures burn at diff= erent rates depending on =0Ahow rich or lean they are. So at a given RPM, = MAP and spark advance you can =0Avary your effective timing by changing the= mixture. =0A =0A=C2=B7 Want to advance your timing? Change your mi= xture to a 50 deg ROP =0Amixture =E2=80=93 which is the fastest burning.=0A= =C2=B7 Want to retard your timing? Make your mixture richer or lea= ner from =0A50 deg ROP.=0A =0AAnd since optimal power is achieved at an eff= ective timing of 16 deg ATDC, =0Aadvancing the spark timing may or MAY NOT = increase horsepower depending on the =0Amixture. But advancing the timing = will likely increase the magnitude of peak =0Aintracylinder pressure leadin= g to higher intracylinder pressures, higher =0Acylinder head temperatures a= nd greater stress =3D shorter enging life.=0A =0AFor those of you who are u= sing electronic ignition (I am not):=0A=C2=B7 Are you sure you are = getting more horsepower? How do you know?=0A=C2=B7 If you are gett= ing more horsepower, are you getting it during all =0Amodes of engine opera= tion? Rich of peak, lean of peak, high MAP, low MAP, etc=0A=C2=B7 = What is happening to your TBO?=0A =0AD. Brunner=0A=0A=0A --0-630661635-1289913968=:47155 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
I certainly agree with the statements below fro= m Mr. Brunner.  A few reinforcing comments:

And, yes, the electronic s= ystem only increases power when it advances timing over the fixed mag AND t= he peak cylinder pressure occurs after 16 ATC.  When is that?  Pr= obably at any mixture when flying at significantly over 10,000 feet (manifo= ld pressures less than 20).  And especially when at low manifold press= ures AND running LOP.  So, in my opinion the advantage is real when ty= pical cruising is done over 10,000 and LOP.  Otherwise the benefits ar= e not all that persuasive.  What about turbocharged engines?  How often are the= y operated at less than 20 inches?  The only problem I see with mags (= on turbocharged engines) is potential for cross-firing within the distribut= or cap, eliminated by most electronic systems.  TBO?  Certainly a= ny time the peak cylinder pressure is increased TBO is reduced.  But I= think a 10:1 engine operated like it was turbocharged (avoid peak EGT like= the plague) could last as long as a standard engine operated more casually= .  And the lower EGT produced by the higher compression is likely to i= ncrease exhaust valve life.
Gary Casey
ES N224SG, IO-540, 10:1, s= ingle Lightspeed, always cruising at 12,000+, LOP

At the risk of starting a =E2=80=9Ctheological=E2= =80=9D controversy, I would like to raise some reservations about electronic ignition systems (other than r= eliability and loss of electrical power)

=  

Peak intracylinder pressure (the p= oint in the combustion cycle at which pressure in the cylinder is highest = =3D effective timing) is related to 3 things; spark timing, rpm and MIXTURE. 

&n= bsp;

Why mixture? Because air and fuel mi= xtures burn at different rates depending on how rich or lean they are. = ; So at a given RPM, MAP and spark advance you can vary your effective timi= ng by changing the mixture. 

=C2=B7    &nbs= p;    Want to advance you= r timing? Change your mixture to a 50 deg ROP mixture =E2=80=93 which is th= e fastest burning.

=C2=B7    &nb= sp;    Want to retard you= r timing?  Make your mixture richer or leaner from 50 deg ROP.<= /p>

 

And since opt= imal power is achieved at an effective timing of 16 deg ATDC, advancing the= spark timing may or MAY NOT increase horsepower de= pending on the mixture.  But advancing the timing will likely increase= the magnitude of peak intracylinder pressure leading to higher intracylind= er pressures, higher cylinder head temperatures and greater stress =3D shor= ter enging life.

 

For those of you who are using electronic ignition (I am = not):

=C2=B7         Are you sure you are getting more horsepower?  How do you = know?

=C2=B7     &= nbsp;   If you are getting mor= e horsepower, are you getting it during all modes of engine operation? = ; Rich of peak, lean of peak, high MAP, low MAP, etc

=C2=B7        &= nbsp;What is happening to your TBO?

 

D. Brunner

=0A=0A=0A

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