On 1/12/2014 2:00 PM, 6pack-request@autox.team.net wrote:
> This is not a racing question. I'm sure the ignition retard is often
> disabled on 6 cylinder Triumphs. Does anyone know why it was used in
> the first place? I have always thought it was strictly for emissions,
> which became more restrictive in 1968. Perhaps it improves combustion
> at low throttle such as when decelerating or when descending a hill.
> Just curious.
> - Larry
There are several types of vacuum that could in general be applied to a
distributor.
Some american cars use something I believe is called port vacuum which
has zero vacuum at idle and then more vacuum as the throttle opens. I
believe something similar to this style of vacuum was used for vacuum
retard on later TR6s. I believe the purpose of this was to lower
combustion pressure and temperature to lower NOX. Later TR6s also had
some kind of temperature switch which changed which port was supplied to
the distributor. Unfortunately I do not understand the purpose of that
switch but I suspect it allowed a little less retard on cold engines
since cold engines need more power and also do not produce as much NOX
anyway.
The manifold vacuum which should be high at idle and go to zero at WOT
is what I believe that was used on early TR6s for vacuum advance.
Traditional vacuum advance like this gives you no advance at WOT but as
you close the throttle for cruise, it advances the ignition for more
power and MPG. I don't think it has a large effect on pollutants but it
does help MPG and it is a shame that it was dropped from the later TR6.
I think the middle years of the TR6 had both vacuum advance and retard.
This is all just my recollection off the top of my head, please correct
me if I am wrong.
ed
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