I believe that the reason that catalyst equipped cars went back to proper
use of ported vacuum and vacuum advance is that the catalyst did most of
the exhaust cleanup so they could again tune the engine for better
performance.
The bottom line is- is you car running OK? the differance between having
good vacuum advance and no vacuum advance is mostly in gas mileage and the
sound of the enging- I find that advancing the timing during cruise makes
the engine sound "free-er (sp?). The use of ported vs. unported vacuum
effects idle quality only. Unless you have to re-time your car to
compensate for too much vacuum advance in some situation, none of this does
anything to the performance level of the engine.
In other words, if it ain't broke don't fix it.
Regards
Bill Eastman
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