>  AB> This is the only issue which I would add to the experimental list.
>  AB> Manifold vacuum is/was the source of choice for hot rodding.
> 
> That is completely incorrect. Any engine will have it's own requirements
As you say, each engine will have its own requirements. Which is why you
should INCLUDE *experimenting* with manifold vacuum.
Theres a bit of an interesting blurb on advance in Rochestor Carberators
(#13) Page 198.
To quote some parts that slant in my favor ;)   [Please note, I'm not trying
to start a flame war. This is OLDCARS afterall, and emmisions equipment does
not exist in my oldcar world]
"Most carburetors provide ports for timed spark and straight manifold
vacuum.  In general, a retarded spark reduces oxides of nitrogen to a
minimum by keeping peak pressures and temperatures at lower values than
would be obtained with an advanced spark setting....this is good for
reducing emmisions-but bad for economy, driveability and heating of
coolant."
"The use of a retarded spark requires richer jetting in the idle and main
systems to get off-idle performance and driveability."
"It must also be considered because high temperatures at idle due to the
retarded spark and high idle-speed settings definitely promote dieseling or
after-run."
Also, 'How to Hot Rod your SBC' mentions manifold vacuum. ;)
Ya, I read enough to be dangerous. =)
> For pure hot rodding, no vaccum advance is used very often. Also some
> heavy duty and truck applications use no vacuum advance.
Point taken,  =) *Street* Rodding then.
> Ported vaccum will not exceed manifold vaccum. If you open the throttle
10-4.
> going up a hill, the ported and manifold vacuum will both drop just the
> same. WHY? Because ported and manifold are the same except in a closed
I can accept that.
> throttle position, at which point port is robbed of vacuum by the throttle
> plate. At any position a little beyond closed throttle, they are always
> the same.
Could one not argue that under idle to just 'a little beyond closed
throttle' manifold vacuum gives you an advantage for a standing start?
(becuase you have manifold vacuum, but no ported vacuum.)
Granted, the time period for this is short, and mechanical advance will take
over. But it is a possibility. =)
Alex.
 | AmiQWK 2.7 - S/N 0261 |
... Life is like.....an analogy.
--- OLMS 2.60p.a1+ [EPMAP55A]
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