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Without the possibility of computer ignition mapping, the most important th=
ing is the maximum total advance. This can start from 3000rpm or higher, de=
pending on the distributor springs.=20
2 degrees is already making a significant difference for horsepower. On a d=
yno one can find at what advance the engine is making the best power, but i=
t is all important to find out if the power is not dropping after 20 or 30 =
seconds (detonation).=20
And the the circumstances on a race week-end can be different : if one is a=
rriving at 30=C2=B0 during a dyno session, it is possible that only 28=C2=
=B0 is safe on a particular day. Total maximum advance can differ considera=
bly (compression ratio,...).=20
I believe that a fresh engine tends to pre-ignition more easily because of =
glowing spots : protruding headgasket(wich should be avoided of course), sh=
arp machining edges...In an older engine the surfaces of the combustion cha=
mbers will be smoother=20
Marcel=20
Van: "fot" <fot@autox.team.net>=20
Aan: "fot" <fot@autox.team.net>=20
Verzonden: Vrijdag 19 maart 2021 23:53:55=20
Onderwerp: Re: [Fot] Distributor centrifugal advance curve for race engine=
=20
When I had crank fire ignition I did test it on the dyno and found that a s=
light retard as RPM's went up helped (at least that's how I remember it - u=
p to 34 / 35 at 3000 rpm but down to 32 at 6000). But with my more vintage =
points system, the advance is "all in" at 3000 rpm. I just set to 30 degree=
s or 32 degrees or if I'm feeling particularly lucky / brave / stupid 34 de=
grees at max. Whatever it ends up at low rpm is where it ends up. When raci=
ng I'm never under 3000 RPM anyway.=20
Regards, Tony=20
On 3/19/2021 5:27 PM, timmmurphh--- via Fot wrote:=20
What advance curve are folks using in their race engines? I have 87mm pisto=
ns, a Kastner G3 cam and about a 12:1 compression ratio. I am using about 1=
9 degrees advance at idle (no centrifugal advance) and 30 degrees advance a=
t 3000 RPM. I don=E2=80=99t know what I have at higher RPM=E2=80=99s becaus=
e I never looked. I=E2=80=99m currently doing an engine rebuild so I will h=
ave to look what I=E2=80=99ve got at the higher RPM=E2=80=99s when I get th=
e engine running. I=E2=80=99m curious as to what others are using and if an=
yone has done any testing on a dyno with different advance curves.=20
Thanks in advance for your input.=20
Tim Murphy=20
#317 BRG TR4=20
_______________________________________________ [ mailto:fot@autox.team.net=
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<html><body><div style=3D"font-family: Verdana, Arial, Helvetica, sans-seri=
f; font-size: 10pt; color: #000000"><div>Without the possibility of compute=
r ignition mapping, the most important thing is the maximum total advance. =
This can start from 3000rpm or higher, depending on the distributor springs=
.</div><div>2 degrees is already making a significant difference for =
horsepower. On a dyno one can find at what advance the engine is making the=
best power, but it is all important to find out if the power is not droppi=
ng after 20 or 30 seconds (detonation).</div><div>And the the circumstances=
on a race week-end can be different : if one is arriving at 30=C2=B0 durin=
g a dyno session, it is possible that only 28=C2=B0 is safe on a particular=
day. Total maximum advance can differ considerably (compression ratio,...)=
.</div><div>I believe that a fresh engine tends to pre-ignition more easily=
because of glowing spots : protruding headgasket(wich should be avoided of=
course), sharp machining edges...In an older engine the surfaces of the co=
mbustion chambers will be smoother</div><div>Marcel</div><div><br></div><hr=
id=3D"zwchr" data-marker=3D"__DIVIDER__"><div data-marker=3D"__HEADERS__">=
<b>Van: </b>"fot" <fot@autox.team.net><br><b>Aan: </b>"fot" <fot@a=
utox.team.net><br><b>Verzonden: </b>Vrijdag 19 maart 2021 23:53:55<br><b=
>Onderwerp: </b>Re: [Fot] Distributor centrifugal advance curve for race en=
gine<br></div><div><br><style>/*<![CDATA[*/p.MsoNormal, li.MsoNormal, div.M=
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/*]]>*/</style></div><div data-marker=3D"__QUOTED_TEXT__"><p>When I had cra=
nk fire ignition I did test it on the dyno and
found that a slight retard as RPM's went up helped (at least
that's how I remember it - up to 34 / 35 at 3000 rpm but down to
32 at 6000). But with my more vintage points system, the advanc=
e
is "all in" at 3000 rpm. I just set to 30 degrees or 32 degrees
or if I'm feeling particularly lucky / brave / stupid 34 degrees
at max. Whatever it ends up at low rpm is where it ends up.&nbs=
p; When
racing I'm never under 3000 RPM anyway.</p>
<p>Regards, Tony<br>
</p>
<div class=3D"moz-cite-prefix">On 3/19/2021 5:27 PM, timmmurphh--- via
Fot wrote:<br>
</div>
<blockquote>
=20
=20
=20
<div class=3D"WordSection1">
<p class=3D"MsoNormal">What advance curve are folks using in their
race engines? I have 87mm pistons, a Kastner G3 cam and about
a 12:1 compression ratio. I am using about 19 degrees advance
at idle (no centrifugal advance) and 30 degrees advance at
3000 RPM. I don=E2=80=99t know what I have at higher RPM=E2=
=80=99s because I
never looked. I=E2=80=99m currently doing an engine rebuild so I =
will
have to look what I=E2=80=99ve got at the higher RPM=E2=80=99s wh=
en I get the
engine running. I=E2=80=99m curious as to what others are using a=
nd if
anyone has done any testing on a dyno with different advance
curves.</p>
<p class=3D"MsoNormal"> </p>
<p class=3D"MsoNormal">Thanks in advance for your input.</p>
<p class=3D"MsoNormal"> </p>
<p class=3D"MsoNormal">Tim Murphy</p>
<p class=3D"MsoNormal">#317 BRG TR4</p>
</div>
<br>
<fieldset class=3D"mimeAttachmentHeader"></fieldset>
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</blockquote>
=20
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