Vacuum advance information and myths

Bewy said

Fishmen,
It seems you might be unaware that Chrys used manifold connected VA to cool the engine?

For 1973-78:
' When engine coolant temps at idle reaches 225*f, the valve opens automatically & applies manifold vacuum directly to the distributor.....This increases engine idle speed & provides additional engine cooling.'

You want to think about why the idle speed increases.....

Click to expand...

That is not unique to Chrysler. It is a provision to address the occassions when the retarded initial timing used for emissions reduction does its job a little too well.

Retarding the initial timing puts more heat into the cylinder walls and helps insure a hotter and more complete burn of the HC. It didn't effect off idle perfromance too much because above idle the advance curve is quick to offset the retarded timing.

Compare the idle rpm of a standard setup verses the same engine of a CAP or CAS equiped engine.
There's a reason why a non-CAP engine can idle at 500 rpm and be put into gear...
Its because the fuel mixture and timing are correct for power and fuel economy with no concern about HC and CO.