Adam:
I am sure others are going to reply, but that has never stopped
me before...
On a '73, it is not a vacuum advance, it is a vacuum retard that
is only engaged at idle. It is an emissions device only. At idle the
timing is retarded to reduce emissions. If the engine gets too warm with
the retarded timing, a thermostat in the top radiator hose shuts off the
retard, and the engine idle speed increases allowing the fan to pull
more air through the radiator to cool the motor.
At cruise or wide open throttle, the retard is disabled, so that
performance is not affected.
Most of the vacuum capsules on the dizzy have long ago perished,
thanks to the fact that they have a rubber diaphragm in them. So if
yours is original, you will want to replace it. 30 year old rubber is
just not going to cut it.
As an aside, vacuum *advance* (as opposed to retard) in general
is highly desirable. It enhances fuel economy substantially at cruise by
advancing the timing far beyond what is possible with a mechanical
advance system. Mechanical advance is controlled by engine speed, vacuum
advance is controlled by engine *load*. At cruise the engine is lightly
loaded and at moderate RPM, so the timing can be advanced over the
mechanical advance with the benefit of much better fuel economy. This is
even more advantageous if the engine has an EGR valve which effectively
leans out the mixture at cruise and reduces pumping losses, giving still
better mileage. One of those rare cases where the emissions technology
actually has other benefits.
Cheers,
Vance
------------------------------
Cogito Ergo Zoom
(I think, therefore I go fast)
TR6 Web page: http://home.comcast.net/~v.navarrette/
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of Adam C Beasley
Sent: March 09, 2005 7:30 AM
To: 6pack@autox.team.net
Subject: Vacuum advance
Is there any reason to use the vacuum advance on my distributor? What
does
advancing the ignition by vacuum accomplish?
Thanks,
Adam
73 TR6
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