On my '79 (vacuum ADVANCE) there is no detectable vacuum from the carb port
at idle. The vacuum at the port increases with the engine speed. When
adjusting the timing (10 BTDC US Spec) there is no difference in the setting
whether the vacuum line is attached or not when the engine is at idle.
Reid
'79 Spitfire (original owner)
-----Original Message-----
From: Douglas Braun & Nadia Papakonstantinou
[mailto:dougnad@bellatlantic.net]
Sent: Wednesday, August 16, 2000 4:15 AM
To: Trevor Boicey; L&B Lubbers; spitfires@autox.team.net
Cc: wizardz; Spitfire (E-mail)
Subject: Re: Distributor vacuum advance - a follow up question and not
as long as Paul's
Oops, Manifold vacuum is MINIMUM at great load!
Remember: Vacuum is the opposite of pressure.
The absolute pressure of the manifold is smallest at idle, and max
(almost the same as atmospheric pressure) at full power.
The amount of gas/air entering the cylinders is roughly
proportional to the manifold pressure.
Supercharged cars can have a manifold pressure GREATER
than atmospheric. This sort of means that their
manifold vacuum is less than zero at high power...
Doug Braun
'72 Spit
At 04:39 AM 8/16/00 -0400, Trevor Boicey wrote:
> One is manifold vacuum, which just measures the vacuum
>in the intake manifold. It's highest at idle and at
>great load, and relatively low at cruise.
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