X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 04 Jan 2008 19:55:41 -0500 Message-ID: X-Original-Return-Path: Received: from mta11.adelphia.net ([68.168.78.205] verified) by logan.com (CommuniGate Pro SMTP 5.2c4) with ESMTP id 2630718 for lml@lancaironline.net; Fri, 04 Jan 2008 08:51:06 -0500 Received-SPF: pass receiver=logan.com; client-ip=68.168.78.205; envelope-from=glcasey@adelphia.net Received: from [75.82.218.90] by mta11.adelphia.net (InterMail vM.6.01.05.02 201-2131-123-102-20050715) with ESMTP id <20080104135025.ZFXL12121.mta11.adelphia.net@[75.82.218.90]> for ; Fri, 4 Jan 2008 08:50:25 -0500 Mime-Version: 1.0 (Apple Message framework v752.2) In-Reply-To: References: Content-Type: multipart/alternative; boundary=Apple-Mail-14--43391759 X-Original-Message-Id: From: Gary Casey Subject: Re: One mag, One electronic ignition X-Original-Date: Fri, 4 Jan 2008 05:50:23 -0800 X-Original-To: "Lancair Mailing List" X-Mailer: Apple Mail (2.752.2) --Apple-Mail-14--43391759 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed The possibility that Steve suggests below is probably real, but remember that the electronic ignition will only advance when the manifold pressure - and hence the cylinder pressure - is lower than the max (only at high altitude or part throttle). And the electronic ignition will only advance 5 or so degrees more than the mag anyway. In 5 or 10 degrees the cylinder pressure will not rise much. I would guess that at higher engine speeds the burn at 10-degrees after ignition is less than 10% complete and probably more like 5%. It is my judgement that there isn't much to worry about, although you are correct that the life of a coil depends on the peak voltage it sees, which goes up with pressure. I'm sure it won't rise to the point that the mag won't fire, though (of course, how would one know?). There isn't much concern related to higher altitudes, because under those conditions the cylinder pressure is lower than at sea level. Since there is evidence to suggest that a coil expected life goes down as the peak voltage goes up should all of us that have one mag be worried? I don't think so, but I don't have firm data to back it up. As I type, though, I think of another issue - say the cylinder pressure rises enough so that even though the manifold pressure is 50% lower than at sea level the firing voltage is not that much less. The coil will still fire, but the likelihood of cross-firing in the distributor is higher. The idea is that the post spacing in the distributor is set assuming the cylinder pressure goes up and down with atmospheric pressure and therefore there will never be a time when the air pressure inside the mag is insufficient to prevent cross-firing. This is what the turbo guys worry about and the cure is to pressurize the magneto, not possible with an NA engine. The symptom would be a rough-running engine at high altitude and full throttle and I've never had that experience. Gary Casey > > From: "Steve Colwell" > Date: January 3, 2008 10:18:04 AM PST > To: lml@lancaironline.net > Subject: One mag, One electronic ignition > > > > I have not done any tests but I believe if One Mag and One Electronic > Ignition is used you are likely to fail the Mag Coil prematurely > (that would > reduce the aprox. 400 to 600 hour normal failure of a new Slick to > a really > unacceptable life). Why?? One of the principal advantages of EI > is the > variable timing advance that improves power and efficiency. When > the EI > fires a plug before the Mag, the pressure rise from earlier > combustion may > prevent the Mag plug from firing. Maybe (probably?) preventing the > Mag plug > from firing at least at higher altitudes where advance is the > greatest. I > base my theory on the old Champion Spark Plug Testers that used an > air hose > to increase pressure while firing a plug to check its ability to > continue to > fire. What do others say? > > > Steve Colwell > > >> Gary said.... >> On the other question about dual electronic ignitions: >> I was thinking about building mine with a dual electronic >> ignition and > the >> power source that I finally came up with (before I abandoned the >> idea in >> favor of using one mag) > > --Apple-Mail-14--43391759 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=ISO-8859-1
The = possibility that Steve suggests below is probably real, but remember = that the electronic ignition will only advance when the manifold = pressure - and hence the cylinder pressure - is lower than the max (only = at high altitude or part throttle).=A0 And the electronic ignition will = only advance 5 or so degrees more than the mag anyway.=A0 In 5 or 10 = degrees the cylinder pressure will not rise much.=A0 I would guess that = at higher engine speeds the burn at 10-degrees after ignition is less = than 10% complete and probably more like 5%.=A0 It is my judgement that = there isn't much to worry about, although you are correct that the life = of a coil depends on the peak voltage it sees, which goes up with = pressure.=A0 I'm sure it won't rise to the point that the mag won't = fire, though (of course, how would one know?).=A0 There isn't much = concern related to higher altitudes, because under those conditions the = cylinder pressure is lower than at sea level. =A0Since there is evidence = to suggest that a coil expected life goes down as the peak voltage goes = up should all of us that have one mag be worried? =A0I don't think so, = but I don't have firm data to back it up.

As I type, = though, I think of another issue - say the cylinder pressure rises = enough so that even though the manifold pressure is 50% lower than at = sea level the firing voltage is not that much less. =A0 The coil will = still fire, but the likelihood of cross-firing in the distributor is = higher.=A0=A0The idea is that the post spacing in the distributor is set = assuming the cylinder pressure goes up and down with atmospheric = pressure and therefore there will never be a time when the air pressure = inside the mag is insufficient to prevent cross-firing. =A0This is what = the turbo guys worry about and the cure is to pressurize the magneto, = not possible with an NA engine. =A0The symptom would be a rough-running = engine at high altitude and full throttle and I've never had that = experience.
Gary Casey


From: = "Steve Colwell" <mcmess1919@yahoo.com>
Date: January 3, 2008 10:18:04 AM = PST
To: lml@lancaironline.net
Subject: One mag, One electronic = ignition


I have = not done any tests but I believe if One Mag and One Electronic
Ignition is used you are likely to fail the Mag Coil = prematurely (that would
reduce the = aprox. 400 to 600 hour normal failure of a new Slick to a = really
unacceptable life).=A0 Why??=A0 One of the principal = advantages of EI is the
variable = timing advance that improves power and efficiency.=A0 When the EI
fires a plug before the Mag, the pressure rise from = earlier combustion may
prevent the Mag plug from = firing.=A0 Maybe = (probably?) preventing the Mag plug
from firing = at least at higher altitudes where advance is the greatest. I
base my theory on the old Champion Spark Plug = Testers that used an air hose
to increase = pressure while firing a plug to check its ability to continue = to
fire.=A0 = What do others say?=A0


Steve Colwell


Gary said....
On the other = question about dual electronic ignitions:
I was = thinking about building mine with a dual electronic ignition=A0 and
the
power source that I finally came up with (before I = abandoned=A0 the idea = in
favor of using one mag)


= --Apple-Mail-14--43391759--