vacuum/engine question

[whitey]

This may sound like a dumb question, I have a comp cams xe268 cam, non-adjustable vacuum advance distributor from Mancini. When the rpm goes up, should vacuum go up or down?

 

[koryliss]

The port for distributor vacuum is used to add more advance in light load (often cruise) conditions when the engine can accept more vacuum. Net is that is very dependent on engine load - mash the throttle and vacuum will drop substantially - even at a fairly high RPM.

 

[fishy68]

When the throttle is opened up you should have practically no vacuum. You might see 1/2 inch but that is about all.

 

[rumblefish360]

Depends on the throttle blades amount of opening.