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Well, I mean, it would be true at some extreme =E2=80=94 for example, =
igniting 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:
>=20
> Max that might be true if the ignition pressure from the combustion =
didn't build so long after the spark...within reasonable limits.
>=20
> On Thu, Apr 2, 2020, 12:11 PM Max Heim <mvheim@sonic.net =
> 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.
>=20
> --
> Max Heim
> '66 MGB
>=20
>> On Apr 1, 2020, at 8:17 PM, Barney Gaylord via Mgs =
>>=20
>> 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". =
Why do we stop spark advance at ~32d BTDC at road speed, and keep the =
advance the same for all higher engine speeds?
>>=20
>>=20
>> 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 =
timing 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 =
sooner.
>>> 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, combustion chamber design, headers etc.=C3=82 =C3=82
>>> Rick
>>> ....
>>=20
>> _______________________________________________
>>=20
>> Donate: http://www.team.net/donate.html =
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>> Suggested annual donation $12.75
>>=20
>> Archive: http://www.team.net/pipermail/mgs =
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>>=20
>> Unsubscribe: =
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<http://autox.team.net/mailman/options/mgs/mvheim@sonic.net>
>>=20
>=20
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<html><head><meta http-equiv=3D"Content-Type" content=3D"text/html =
charset=3Dutf-8"></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" =
class=3D"">Well, I mean, it would be true at some extreme =E2=80=94 for =
example, igniting the spark at the very beginning of the compression =
stroke. But I suspect Barney was getting at something else.<div =
class=3D""><br class=3D""><div class=3D"">
<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; -webkit-text-stroke-width: 0px; word-wrap: =
break-word; -webkit-nbsp-mode: space; -webkit-line-break: =
after-white-space;" class=3D""><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; =
-webkit-text-stroke-width: 0px; word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" =
class=3D""><div style=3D"margin: 0px; font-size: 13px;" =
class=3D"">--</div><div style=3D"margin: 0px; font-size: 13px; =
min-height: 16px;" class=3D"">Max Heim</div><div style=3D"margin: 0px; =
font-size: 13px;" class=3D"">'66 MGB</div></div></div>
</div>
<br class=3D""><div><blockquote type=3D"cite" class=3D""><div =
class=3D"">On Apr 2, 2020, at 11:24 AM, Richard Lindsay <<a =
href=3D"mailto:richardolindsay@gmail.com"; =
class=3D"">richardolindsay@gmail.com</a>> wrote:</div><br =
class=3D"Apple-interchange-newline"><div class=3D""><div dir=3D"auto" =
class=3D""><div class=3D"">Max that might be true if the ignition =
pressure from the combustion didn't build so long after the =
spark...within reasonable limits.<br class=3D""><br class=3D""><div =
class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Thu, Apr =
2, 2020, 12:11 PM Max Heim <<a href=3D"mailto:mvheim@sonic.net"; =
class=3D"">mvheim@sonic.net</a>> wrote:<br class=3D""></div><blockquote=
class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc =
solid;padding-left:1ex"><div style=3D"word-wrap:break-word" =
class=3D"">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 class=3D""><br class=3D""><div class=3D"">
<div style=3D"letter-spacing: normal; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; word-spacing: 0px; =
word-wrap: break-word;" class=3D""><div style=3D"letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; word-wrap: break-word;" class=3D""><div =
style=3D"margin:0px;font-size:13px" class=3D"">--</div><div =
style=3D"margin:0px;font-size:13px;min-height:16px" class=3D"">Max =
Heim</div><div style=3D"margin:0px;font-size:13px" class=3D"">'66 =
MGB</div></div></div>
</div>
<br class=3D""><div class=3D""><blockquote type=3D"cite" class=3D""><div =
class=3D"">On Apr 1, 2020, at 8:17 PM, Barney Gaylord via Mgs <<a =
href=3D"mailto:mgs@autox.team.net"; target=3D"_blank" rel=3D"noreferrer" =
class=3D"">mgs@autox.team.net</a>> wrote:</div><br class=3D""><div =
class=3D""><div class=3D"">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". Why do we stop spark advance at ~32d =
BTDC at road speed, and keep the advance the same for all higher engine =
speeds?<br class=3D""><br class=3D""><br class=3D"">At 07:56 PM =
4/1/2020, Richard Ewald via Mgs wrote:<br class=3D""><blockquote =
type=3D"cite" class=3D"">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.<br =
class=3D"">At idle speed 3ms is about 15 degrees.=C3=82 =C3=82<br =
class=3D"">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 timing is 5 BTDC.<br class=3D"">If you look at =
tune up specs for non smog controlled engines, most have base timing in =
the 5-10 BTDC range.<br class=3D"">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 class=3D"">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, combustion =
chamber design, headers etc.=C3=82 =C3=82<br class=3D"">Rick<br =
class=3D"">....<br class=3D""></blockquote><br =
class=3D"">_______________________________________________<br =
class=3D""><br class=3D""><a href=3D"mailto:Mgs@autox.team.net"; =
target=3D"_blank" rel=3D"noreferrer" class=3D"">Mgs@autox.team.net</a><br =
class=3D"">Donate: <a href=3D"http://www.team.net/donate.html"; =
target=3D"_blank" rel=3D"noreferrer" =
class=3D"">http://www.team.net/donate.html</a><br class=3D"">Suggested =
annual donation $12.75<br class=3D""><br class=3D"">Archive: <a =
href=3D"http://www.team.net/pipermail/mgs"; target=3D"_blank" =
rel=3D"noreferrer" class=3D"">http://www.team.net/pipermail/mgs</a> <a =
href=3D"http://autox.team.net/archive"; target=3D"_blank" =
rel=3D"noreferrer" class=3D"">http://autox.team.net/archive</a><br =
class=3D""><br class=3D"">Unsubscribe: <a =
href=3D"http://autox.team.net/mailman/options/mgs/mvheim@sonic.net"; =
target=3D"_blank" rel=3D"noreferrer" =
class=3D"">http://autox.team.net/mailman/options/mgs/mvheim@sonic.net</a><=
br class=3D""><br class=3D""></div></div></blockquote></div><br =
class=3D""></div></div></blockquote></div></div></div>
</div></blockquote></div><br class=3D""></div></body></html>=
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