Jay:
The thermal vacuum switch does not influence the function of the
EGR on
the TR6. The EGR valve is closed at idle, and closed at wide open
throttle
(WOT) but is open at cruise. It dilutes the amount of oxygen in the
combustion
chamber with an inert gas (carbon dioxide) which in turn reduces the
peak
combustion temperature and thereby reduces NOx. A side benefit is that
gas
mileage goes up, since pumping losses are reduced under cruise
conditions.
The thermal vacuum switch opens when the engine is fully warmed,
and
retards the timing by 14-16 degrees to reduce emissions at idle. When
the
engine is at WOT or cruise conditions, the vacuum retard is disabled, so
that the motor runs with mechanical advance only. This also means that
your "fast idle" function on a cold engine is dependant on the vacuum
retard being disabled, and that being able to obtain the correct
"slow idle" speed when the engine is warmed up depends on the vacuum
retard being enabled.
Disabling the vacuum retard will make it more difficult to
obtain
the correct fast/slow idle function during the warm-up of the motor.
Cheers,
Vance
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of Jay Welch
Sent: Tuesday, May 04, 2004 5:10 AM
To: fetnerj001@hawaii.rr.com
Cc: DaCRANEz@aol.com; 6pack@autox.team.net
Subject: Re: vacuum retard
I don't have a TR6 vacuum map in front of me and don't have an EGR on my
car but I believe on most cars, the thermal switch is used to delay EGR
and/or spark advance until the engine has warmed. My understding is
that EGR is actually used to cool the combuston chamber temps. Is it
possible that Triumph designed their thermal switch for a similar
function?
Jay Welch
Abington, MA
TR6s
Member Cape Cod British Car Club CCBCC
http://www.capecodbritishcarclub.org/
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