[Mgs] Engine maths...and spare time

[Richard Lindsay]

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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