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Paul shared these sage words,
> Most of what the engine is doing at idle is as a vacuum pump,
> generating about 16 in Hg. or so in the intake manifold, and is
> why when you introduce an intake vacuum leak the idle speed
> goes up. This may be included in your 'other forces' above.
>
> Whist there may well be a most efficient point to start combustion
> and the flame front, the prime consideration has to be avoiding
> spontaneous combustion at any point, i.e. pinking or detonation.
> As the flame front travels pressure inside the engine is rising,
> but after TDC the volume available is reducing, which tends to
> counteract the pressure increase. There is also the effect of
> leverage i.e. the angle the con rod makes relative to the piston.
>
> I'm certainly not going to check your maths, a specific engine is
> what it is, and the timing has to be set taking those specifics
> into account plus other factors like fuel grade and type.
>
> PaulH.
In a follow-on note I recommended Colin Campbell's landmark engine
manual for LBC owners, 'The Sports Car Engine: Its Tuning and
Modification'. Here's a page from that book addressing the combustion
process. All credit to Dr. Campbell.
http://aubard.us/53_MG/20200328_113435.jpg
I feel that this discussion is of little interest to the average LBC
owner but its been quiet here and we all have delete keys, so hopefully,
minimum foul.
Rick
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<div dir=3D"ltr">Paul shared these sage words,<br><br>> Most of what the=
engine is doing at idle is as a vacuum pump,<div>> generating about 16 =
in Hg. or so in the intake manifold, and is</div><div>> why when you int=
roduce an intake vacuum leak the idle speed</div><div>> goes up.=C2=A0 T=
his may be included in your 'other forces' above.<br>>=C2=A0<br>=
> Whist there may well be a most efficient point to start combustion</di=
v><div>> and the flame front, the prime consideration has to be avoiding=
</div><div>> spontaneous combustion at any point, i.e. pinking or detona=
tion.</div><div>> As the flame front travels pressure inside the engine =
is rising,</div><div>> but after TDC the volume available is reducing, w=
hich tends to</div><div>> counteract the pressure increase.=C2=A0 There =
is also the effect of</div><div>> leverage i.e. the angle the con rod ma=
kes relative to the piston.<br>>=C2=A0<br>> I'm certainly not goi=
ng to check your maths, a specific engine is</div><div>> what it is, and=
the timing has to be set taking those specifics</div><div>> into accoun=
t plus other factors like fuel grade and type.<br>>=C2=A0<br>> PaulH.=
</div><div><br></div><div>=C2=A0 =C2=A0In a follow-on note I recommended Co=
lin Campbell's landmark engine manual for LBC owners, 'The Sports C=
ar Engine: Its Tuning and Modification'. Here's a page from that bo=
ok addressing the combustion process. All credit to Dr. Campbell.</div><div=
><br></div><div><a href=3D"http://aubard.us/53_MG/20200328_113435.jpg";>http=
://aubard.us/53_MG/20200328_113435.jpg</a></div><div><br></div><div>=C2=A0 =
=C2=A0I feel that this discussion is of little interest to the average LBC =
owner but its been quiet here and we all have delete keys, so hopefully, mi=
nimum foul.</div><div><br></div><div>Rick=C2=A0<br></div></div>
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![http://aubard.us/53_MG/20200328_113435.jpg"](http://aubard.us/53_MG/20200328_113435.jpg"){kind=link}