This is a multi-part message in MIME format.
--===============5912332146780455162==
boundary="----=_NextPart_000_00A4_01D4FAA4.9A7F6DD0"
This is a multi-part message in MIME format.
------=_NextPart_000_00A4_01D4FAA4.9A7F6DD0
charset="utf-8"
Content-Transfer-Encoding: quoted-printable
"until you notice preignition" Is a bit drastic. Haynes says to drive =
at full throttle in 4th from 30 to 50 and advance until faint pinking =
can be heard. However I've noticed that I can get pinking at part =
throttle and opening the throttle further stops it, either because the =
bigger charge cools the combustion chamber more, or the vacuum advance =
backs off. So I use the criteria 'at any combination of throttle, revs =
and load' and keep it just short of that. =20
The reason Haynes says that you can benefit from advancing it over book =
values is that with the level of engineering used in our engines some =
will be more prone to pinking than others,and the book caters for the =
worst case, and maybe with a bit of a safety factor. That was =
definitely the case with an A-series in the 70s, which as a new car and =
dealer serviced always came back running like a dog (comparatively) as =
they always put it back to book. But on my 73 MGB I couldn't run more =
than book, even on leaded, and have to retard slightly from that on =
unleaded even 99 octane.
Whether it pinks or not also depends on terrain. Living in a relatively =
flat part of the world I don't get pinking, but when touring in Wales =
and other mountainous areas it can. The 25D4 distributor is a great =
benefit here as it allows one to retard the timing a degree or two very =
easily, also if one can't get higher octane fuel in rural areas.
Completely agree with your reasoning behind centrifugal and vacuum =
advance, but:
"The other is pressure operated, offering advance when the twin turbos =
raise the plenum pressure above ambient."
Are you sure that isn't vacuum retard? If the turbos were increasing =
the pressure I'd expect that to make spontaneous combustion more likely, =
needing retarding to control.
PaulH.
----- Original Message -----=20
I write to open a discussion about ignition timing. Over on the =
Triumph forum ( Apologies for using profanity. ) a member wrote, "Just =
advance the timing until you notice preignition." Now I recognize that =
Triumphs use farm implement engines, but that advice seems a bit =
sketchy. So let me write a preface then ask a question.
------=_NextPart_000_00A4_01D4FAA4.9A7F6DD0
charset="utf-8"
Content-Transfer-Encoding: quoted-printable
=EF=BB=BF<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content=3D"text/html; charset=3Dutf-8" http-equiv=3DContent-Type>
<META name=3DGENERATOR content=3D"MSHTML 8.00.6001.23588">
<STYLE></STYLE>
</HEAD>
<BODY bgColor=3D#ffffff>
<DIV><FONT size=3D2>"</FONT><FONT size=3D3>until you notice =
preignition" Is a=20
bit drastic. Haynes says to drive at full throttle in 4th from 30 =
to 50=20
and advance until faint pinking can be heard. However I've noticed =
that I=20
can get pinking at part throttle and opening the throttle further stops =
it,=20
either because the bigger charge cools the combustion chamber more, =
or the=20
vacuum advance backs off. So I use the criteria 'at any =
combination of=20
throttle, revs and load' and keep it just short of that. =
</FONT></DIV>
<DIV><FONT size=3D3></FONT> </DIV>
<DIV><FONT size=3D3>The reason Haynes says that you can benefit from =
advancing it=20
over book values is that with the level of engineering used in our =
engines some=20
will be more prone to pinking than others,and the book caters for the =
worst=20
case, and maybe with a bit of a safety factor. That was definitely =
the=20
case with an A-series in the 70s, which as a new car and dealer serviced =
always=20
came back running like a dog (comparatively) as they always put it back =
to=20
book. But on my 73 MGB I couldn't run more than book, even on =
leaded, and=20
have to retard slightly from that on unleaded even 99 =
octane.</FONT></DIV>
<DIV><FONT size=3D3></FONT> </DIV>
<DIV><FONT size=3D3>Whether it pinks or not also depends on =
terrain. Living=20
in a relatively flat part of the world I don't get pinking, but when =
touring in=20
Wales and other mountainous areas it can. The 25D4 distributor is =
a great=20
benefit here as it allows one to retard the timing a degree or two very =
easily,=20
also if one can't get higher octane fuel in rural areas.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>Completely agree with your reasoning behind =
centrifugal and=20
vacuum advance, but:</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>"</FONT><FONT size=3D3>The other is pressure =
operated, offering=20
advance when the twin turbos raise the plenum pressure above=20
ambient."</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Are you sure that isn't vacuum retard? If the =
turbos=20
were increasing the pressure I'd expect that to make spontaneous =
combustion more=20
likely, needing retarding to control.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>PaulH.</FONT></DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; =
PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV=20
style=3D"FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: =
black"> I=20
write to open a discussion about ignition timing. Over on the Triumph =
forum (=20
Apologies for using profanity. ) a member wrote, "Just advance the =
timing=20
until you notice preignition." Now I recognize that Triumphs use farm=20
implement engines, but that advice seems a bit sketchy. So let me =
write a=20
preface then ask a question.</DIV>
<DIV dir=3Dauto><FONT =
size=3D2></FONT> </DIV></BLOCKQUOTE></BODY></HTML>
------=_NextPart_000_00A4_01D4FAA4.9A7F6DD0--
--===============5912332146780455162==
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
_______________________________________________
Mgs@autox.team.net
Archive: http://www.team.net/pipermail/mgs
Unsubscribe: http://autox.team.net/mailman/options/mgs/mharc@autox.team.net
--===============5912332146780455162==--
|