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As I wrote in the thread's original post, "I love dynamic systems!" Even
more fascinating when multi-dimensional.
R
On Thu, Apr 2, 2020, 4:31 PM Richard Ewald <richard.ewald@gmail.com> wrote:
> Remember the intake valves stay open for a bit past BDC as the piston
> starts up, also to get the mixture to go from flammable to flat out
> explosive the charge has to be compressed. so those factors tend to limi=
t
> how much effective timing you can have.
> Going a little deeper when you are using a mechanical distributor with
> weights there is only so much refinement you can get in your advance
> curve. Once you get into fully electronic ignition systems, there are
> systems that have upward to 70 degrees of range from fully retard to full
> advance (they may not use it in all applications, but the capability is
> there in the electronics)
> Rick
>
> On Thu, Apr 2, 2020 at 11:33 AM Max Heim <mvheim@sonic.net> wrote:
>
>> Well, I mean, it would be true at some extreme =E2=80=94 for example, ig=
niting
>> the spark at the very beginning of the compression stroke. But I suspect
>> Barney was getting at something else.
>>
>> --
>> Max Heim
>> '66 MGB
>>
>> On Apr 2, 2020, at 11:24 AM, Richard Lindsay <richardolindsay@gmail.com>
>> wrote:
>>
>> Max that might be true if the ignition pressure from the combustion
>> didn't build so long after the spark...within reasonable limits.
>>
>> On Thu, Apr 2, 2020, 12:11 PM Max Heim <mvheim@sonic.net> wrote:
>>
>>> Well, it seems to me that if you advance the spark to a point on the
>>> compression stroke where the piston is still coming up, the expanding
>>> ignited mixture would be fighting the piston, and it would actually red=
uce
>>> power. I=E2=80=99m not sure if that is what you are talking about, thou=
gh.
>>>
>>> --
>>> Max Heim
>>> '66 MGB
>>>
>>> On Apr 1, 2020, at 8:17 PM, Barney Gaylord via Mgs <mgs@autox.team.net>
>>> wrote:
>>>
>>> Okay, let's see if anyone knows the answer to this one. Why is it that
>>> "You do eventually get to a point where no more advance will help". Wh=
y do
>>> we stop spark advance at ~32d BTDC at road speed, and keep the advance =
the
>>> same for all higher engine speeds?
>>>
>>>
>>> At 07:56 PM 4/1/2020, Richard Ewald via Mgs wrote:
>>>
>>> It takes about 3ms to burn the fuel in a cylinder from when the spark
>>> ignites it.=C3=82 The engine designers=C3=82 want the peak pressure to=
occur at
>>> between 5-10 ATDC.
>>> At idle speed 3ms is about 15 degrees.=C3=82 =C3=82
>>> So if you want your peak pressure at 5 ATDC, your base timing=C3=82 is =
10
>>> BTDC, if=C3=82 you want=C3=82 your peak pressure at 10 ATDC your timi=
ng is 5 BTDC.
>>> If you look at tune up specs for non smog controlled engines, most have
>>> base timing in the 5-10 BTDC range.
>>> Now if you double the engine speed, it still take 3ms to burn, but to
>>> keep the max pressure at 5-10 ATDC, you have to light the mixture soone=
r.
>>> You do eventually=C3=82 get to a point where no more advance will help.=
=C3=82
>>> That point varies with the engine=C3=82 design,=C3=82 cam profile, co=
mbustion
>>> chamber design, headers etc.=C3=82 =C3=82
>>> Rick
>>> ....
>>>
>>>
>>> _______________________________________________
>>>
>>> Mgs@autox.team.net
>>> Donate: http://www.team.net/donate.html
>>> Suggested annual donation $12.75
>>>
>>> Archive: http://www.team.net/pipermail/mgs http://autox.team.net/archiv=
e
>>>
>>> Unsubscribe: http://autox.team.net/mailman/options/mgs/mvheim@sonic.net
>>>
>>>
>>>
>>
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<div dir=3D"auto">As I wrote in the thread's original post, "I lov=
e dynamic systems!" Even more fascinating when multi-dimensional.=C2=
=A0<div dir=3D"auto"><br></div><div dir=3D"auto">R</div></div><br><div clas=
s=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Thu, Apr 2, 2020=
, 4:31 PM Richard Ewald <<a href=3D"mailto:richard.ewald@gmail.com";>rich=
ard.ewald@gmail.com</a>> wrote:<br></div><blockquote class=3D"gmail_quot=
e" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">=
<div dir=3D"ltr">Remember the intake valves stay open for a bit past BDC as=
the piston starts up, also to get the mixture to go from flammable=C2=A0to=
flat out explosive the charge has to be compressed.=C2=A0 so those factors=
tend to limit how much effective timing you can have.=C2=A0=C2=A0<div>Goin=
g a little deeper when you are using a mechanical distributor=C2=A0with wei=
ghts there is only so much refinement you can get in your advance curve.=C2=
=A0 Once you get into fully electronic ignition systems, there are systems =
that have upward to 70 degrees of range from fully retard to full advance (=
they may not use it in all applications, but the capability is there in the=
electronics)</div><div>Rick</div></div><br><div class=3D"gmail_quote"><div=
dir=3D"ltr" class=3D"gmail_attr">On Thu, Apr 2, 2020 at 11:33 AM Max Heim =
<<a href=3D"mailto:mvheim@sonic.net"; target=3D"_blank" rel=3D"noreferrer=
">mvheim@sonic.net</a>> wrote:<br></div><blockquote class=3D"gmail_quote=
" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);=
padding-left:1ex"><div>Well, I mean, it would be true at some extreme =E2=
=80=94 for example, igniting the spark at the very beginning of the compres=
sion stroke. But I suspect Barney was getting at something else.<div><br><d=
iv>
<div style=3D"color:rgb(0,0,0);letter-spacing:normal;text-align:start;text-=
indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><div st=
yle=3D"color:rgb(0,0,0);letter-spacing:normal;text-align:start;text-indent:=
0px;text-transform:none;white-space:normal;word-spacing:0px"><div style=3D"=
margin:0px;font-size:13px">--</div><div style=3D"margin:0px;font-size:13px;=
min-height:16px">Max Heim</div><div style=3D"margin:0px;font-size:13px">=
9;66 MGB</div></div></div>
</div>
<br><div><blockquote type=3D"cite"><div>On Apr 2, 2020, at 11:24 AM, Richar=
d Lindsay <<a href=3D"mailto:richardolindsay@gmail.com"; target=3D"_blank=
" rel=3D"noreferrer">richardolindsay@gmail.com</a>> wrote:</div><br><div=
><div dir=3D"auto"><div>Max that might be true if the ignition pressure fro=
m the combustion didn't build so long after the spark...within reasonab=
le limits.<br><br><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmai=
l_attr">On Thu, Apr 2, 2020, 12:11 PM Max Heim <<a href=3D"mailto:mvheim=
@sonic.net" target=3D"_blank" rel=3D"noreferrer">mvheim@sonic.net</a>> w=
rote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0p=
x 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div>Well,=
it seems to me that if you advance the spark to a point on the compression=
stroke where the piston is still coming up, the expanding ignited mixture =
would be fighting the piston, and it would actually reduce power. I=E2=80=
=99m not sure if that is what you are talking about, though.<div><br><div>
<div style=3D"letter-spacing:normal;text-align:start;text-indent:0px;text-t=
ransform:none;white-space:normal;word-spacing:0px"><div style=3D"letter-spa=
cing:normal;text-align:start;text-indent:0px;text-transform:none;white-spac=
e:normal;word-spacing:0px"><div style=3D"margin:0px;font-size:13px">--</div=
><div style=3D"margin:0px;font-size:13px;min-height:16px">Max Heim</div><di=
v style=3D"margin:0px;font-size:13px">'66 MGB</div></div></div>
</div>
<br><div><blockquote type=3D"cite"><div>On Apr 1, 2020, at 8:17 PM, Barney =
Gaylord via Mgs <<a href=3D"mailto:mgs@autox.team.net"; rel=3D"noreferrer=
noreferrer" target=3D"_blank">mgs@autox.team.net</a>> wrote:</div><br><=
div><div>Okay, let's see if anyone knows the answer to this one.=C2=A0 =
Why is it that "You do eventually get to a point where no more advance=
will help".=C2=A0 Why do we stop spark advance at ~32d BTDC at road s=
peed, and keep the advance the same for all higher engine speeds?<br><br><b=
r>At 07:56 PM 4/1/2020, Richard Ewald via Mgs wrote:<br><blockquote type=3D=
"cite">It takes about 3ms to burn the fuel in a cylinder from when the spar=
k ignites it.=C3=82 =C2=A0The engine designers=C3=82 want the peak pressure=
to occur at between 5-10 ATDC.<br>At idle speed 3ms is about 15 degrees.=
=C3=82 =C3=82<br>So if you want your peak pressure at 5 ATDC, your base tim=
ing=C3=82 is 10 BTDC, if=C3=82 =C2=A0you want=C3=82 =C2=A0your peak pressur=
e at 10 ATDC your timing is 5 BTDC.<br>If you look at tune up specs for non=
smog controlled engines, most have base timing in the 5-10 BTDC range.<br>=
Now if you double the engine speed, it still take 3ms to burn, but to keep =
the max pressure at 5-10 ATDC, you have to light the mixture sooner.<br>You=
do eventually=C3=82 get to a point where no more advance will help.=C3=82 =
=C2=A0That point varies with the engine=C3=82 design,=C3=82 =C2=A0cam profi=
le, combustion chamber design, headers etc.=C3=82 =C2=A0=C3=82<br>Rick<br>.=
...<br></blockquote><br>_______________________________________________<br>=
<br><a href=3D"mailto:Mgs@autox.team.net"; rel=3D"noreferrer noreferrer" tar=
get=3D"_blank">Mgs@autox.team.net</a><br>Donate: <a href=3D"http://www.team=
.net/donate.html" rel=3D"noreferrer noreferrer" target=3D"_blank">http://ww=
w.team.net/donate.html</a><br>Suggested annual donation =C2=A0$12.75<br><br=
>Archive: <a href=3D"http://www.team.net/pipermail/mgs"; rel=3D"noreferrer n=
oreferrer" target=3D"_blank">http://www.team.net/pipermail/mgs</a> <a href=
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heim@sonic.net</a><br><br></div></div></blockquote></div><br></div></div></=
blockquote></div></div></div>
</div></blockquote></div><br></div></div></blockquote></div>
</blockquote></div>
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