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From: Gary Casey <casey.gary@yahoo.com>
Reply-To: Gary Casey <casey.gary@yahoo.com>
Subject: Re: E-Mag/P-Mag
In-Reply-To: <listdigest-5212774@logan.com>
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Chris,=0AI wish I had really hard numbers on the benefit.=A0 If you read so=
me of the stuff from suppliers, you could get the idea that there is an "up=
 to" 20 percent improvement at altitude.=A0 I don't think that the average =
user will see that much, but the benefit is still substantial.=A0 The engin=
e will produce most power if the spark is adjusted so that the peak cylinde=
r pressure occurs at about 16 degrees after top center (ATC) and that is pr=
etty much independent of engine type and operating condition.=A0 The proble=
m is that the flame speed varies, depending on a number of parameters.=A0 P=
robably the only two that are pertinent are manifold pressure and mixture.=
=A0 You might think that engine speed is important (higher speed gives the =
flame less time to propagate), but the turbulence in the chamber increases =
as the engine speed increases and that speeds up the flame travel enough or=
 nearly enough to negate that effect.=0A=A0=0AThe flame travels essentially=
 by "jumping" from one "treetop" of fuel to the next, so when the fuel mole=
cules are further apart the flame travel is slower.=A0 That delays the poin=
t at which maximum cylinder pressure occurs.=A0 So naturally, lower manifol=
d pressure results in slower flame speed and leads to the requirement for m=
ore spark advance.=A0 The same is true for leaner mixtures as that increase=
s the distance between fuel molecules.=A0 Somewhat counter-intuitive is tha=
t the same thing happens with richer-than-stoichiometric mixtures, but that=
's a different topic.=A0 The peak flame speed occurs at roughly stoichimetr=
ic mixtures, which turns out to be about 50 degrees rich of peak.=A0 And th=
e important thing is that the flame travel will slow progressively faster a=
nd faster (does that make sense?=A0 I hope so) as the mixture gets lean or =
the manifold pressure is reduced.=A0 The reason is that after TDC the volum=
e in the combustion chamber is increasing and
 that by itself slows the combustion (more distance between molecules).=A0 =
So if the combustion doesn't come close to completion soon enough it will t=
ake a long, long=A0time.=0A=A0=0AThe common electronic ignition systems adv=
ance the spark as a function of only manifold pressure - at least as far as=
 I know.=A0 At altitudes above 12,000 feet you can expect that the timing w=
ill be several degrees advanced from that at sea level.=A0 That gives a cer=
tain benefit.=A0 I think the real improvement comes from running LOP at hig=
h altitude.=A0 If you try to run LOP at very high altitude without the extr=
a spark advance the power output will drop faster than one might expect, es=
sentially falling off the cliff.=A0 So yes, if you want to run at, say, 15,=
000=A0AND LOP the extra spark advance could improve the efficiency of the e=
ngine by maybe 20 percent.=A0 In this case I say "efficiency" as opposed to=
 power because the LOP operation will reduce the power output - the spark a=
dvance will just keep it from reducing as much.=0A=A0=0AIn theory, at least=
 you could then run at a fixed IAS at a higher altitude than you could othe=
rwise and reduce the fuel consumption by that 20 percent.=A0 But if you wan=
t to go as fast as possible at a given altitude you won't be running LOP an=
d then I suspect the improvement in speed at=A0that fixed altitude could be=
 about 2 percent.=0A=A0=0AIt's not a simple subject, but I hope I've shed a=
 little light on it.=A0 How much improvement can you expect by running only=
 one electronic ignition?=A0 I've been told roughly half.=0A=A0=0AGary Case=
y - sorry about the long post.=0A=A0=0AFrom chris:=0AGary,=0ACould you elab=
orate on the performance benefits to be expected from advanced spark at alt=
itude.  Efficiency, power, etc.=0A-just curious as I spend a lot of time be=
tween 13 and 18k with my Slick mags and carb. and haven't really studied th=
e topic.=0Athanks, =0AChris Zavatson
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<html><body><div style=3D"color:#000; background-color:#fff; font-family:bo=
okman old style, new york, times, serif;font-size:12pt"><div>Chris,</div><d=
iv>I wish I had really hard numbers on the benefit.&nbsp; If you read some =
of the stuff from suppliers, you could get the idea that there is an "up to=
" 20 percent improvement at altitude.&nbsp; I don't think that the average =
user will see that much, but the benefit is still substantial.&nbsp; The en=
gine will produce most power if the spark is adjusted so that the peak cyli=
nder pressure occurs at about 16 degrees after top center (ATC) and that is=
 pretty much independent of engine type and operating condition.&nbsp; The =
problem is that the flame speed varies, depending on a number of parameters=
.&nbsp; Probably the only two that are pertinent are manifold pressure and =
mixture.&nbsp; You might think that engine speed is important (higher speed=
 gives the flame less time to propagate), but the turbulence in the
 chamber increases as the engine speed increases and that speeds up the fla=
me travel enough or nearly enough to negate that effect.</div><div>&nbsp;</=
div><div>The flame travels essentially by "jumping" from one "treetop" of f=
uel to the next, so when the fuel molecules are further apart the flame tra=
vel is slower.&nbsp; That delays the point at which maximum cylinder pressu=
re occurs.&nbsp; So naturally, lower manifold pressure results in slower fl=
ame speed and leads to the requirement for more spark advance.&nbsp; The sa=
me is true for leaner mixtures as that increases the distance between fuel =
molecules.&nbsp; Somewhat counter-intuitive is that the same thing happens =
with richer-than-stoichiometric mixtures, but that's a different topic.&nbs=
p; The peak flame speed occurs at roughly stoichimetric mixtures, which tur=
ns out to be about 50 degrees rich of peak.&nbsp; And the important thing i=
s that the flame travel will slow progressively faster and faster
 (does that make sense?&nbsp; I hope so) as the mixture gets lean or the ma=
nifold pressure is reduced.&nbsp; The reason is that after TDC the volume i=
n the combustion chamber is increasing and that by itself slows the combust=
ion (more distance between molecules).&nbsp; So if the combustion doesn't c=
ome close to completion soon enough it will take a long, long&nbsp;time.</d=
iv><div>&nbsp;</div><div>The common electronic ignition systems advance the=
 spark as a function of only manifold pressure - at least as far as I know.=
&nbsp; At altitudes above 12,000 feet you can expect that the timing will b=
e several degrees advanced from that at sea level.&nbsp; That gives a certa=
in benefit.&nbsp; I think the real improvement comes from running LOP at hi=
gh altitude.&nbsp; If you try to run LOP at very high altitude without the =
extra spark advance the power output will drop faster than one might expect=
, essentially falling off the cliff.&nbsp; So yes, if you want to
 run at, say, 15,000&nbsp;AND LOP the extra spark advance could improve the=
 efficiency of the engine by maybe 20 percent.&nbsp; In this case I say "ef=
ficiency" as opposed to power because the LOP operation will reduce the pow=
er output - the spark advance will just keep it from reducing as much.</div=
><div>&nbsp;</div><div>In theory, at least you could then run at a fixed IA=
S at a higher altitude than you could otherwise and reduce the fuel consump=
tion by that 20 percent.&nbsp; But if you want to go as fast as possible at=
 a given altitude you won't be running LOP and then I suspect the improveme=
nt in speed at&nbsp;that fixed altitude could be about 2 percent.</div><div=
>&nbsp;</div><div>It's not a simple subject, but I hope I've shed a little =
light on it.&nbsp; How much improvement can you expect by running only one =
electronic ignition?&nbsp; I've been told roughly half.</div><div>&nbsp;</d=
iv><div>Gary Casey - sorry about the long
 post.</div><div>&nbsp;</div><div>From chris:</div><div id=3D"yiv286319086y=
ui_3_2_0_16_132184289601043"><span id=3D"yiv286319086yui_3_2_0_16_132184289=
601059">Gary,</span></div><div><span id=3D"yiv286319086yui_3_2_0_16_1321842=
89601073">Could you elaborate on the performance benefits to be expected fr=
om advance<var id=3D"yiv286319086yui-ie-cursor"></var>d spark at altitude. =
 Efficiency, power, etc.</span></div><div id=3D"yiv286319086yui_3_2_0_16_13=
21842896010698"><span id=3D"yiv286319086yui_3_2_0_16_1321842896010409">-jus=
t curious as I spend a lot of time between 13 and 18k with my Slick mags an=
d <span id=3D"yiv286319086misspell-0" class=3D"yiv286319086mark">carb</span=
>. and haven't really studied the topic.</span></div><div id=3D"yiv28631908=
6yui_3_2_0_16_13218428960101064"><span id=3D"yiv286319086yui_3_2_0_16_13218=
42896010891">thanks,</span> </div><div><span id=3D"yiv286319086yui_3_2_0_16=
_1321842896010915">Chris Zavatson</span></div><div><font size=3D"2"
 face=3D"Arial"></font>&nbsp;</div></div></body></html>
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