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If you are driving on the street and your distributor has a vacuum advance unit on it, use it. Most Mopars ( from the factory ) ran ported vacuum. If you are running stock stuff, run ported vacuum. If you are running a pretty hot cam and have idle issues. switch over to manifold vacuum. The extra advance at idle will help with idle quality. Mileage will be better if you use the vacuum advance, not to mention the motor will run cooler.



People who know nothing about tuning a performance car compensate by putting the vacuum advance on manifold vacuum. It helps hold the idle for those with lack of tuning ability. But at WOT there is no vacuum and you give up a huge amount of Performance! Some people should not be offering up advice period!

Right! Vacuum advance has nothing to do with performance - at WOT. Vacuum advance is ment for idle and cruise, when you want to lite that mixture earlier to maintain that peak cylinder pressure at 10-15 degrees ATDC. On engines with big cams where you need lots of air at idle, running manifold vacuum ( dumping in an extra 8-10 of advance )can help keep you out of the fuel transition slots by letting you close those throttle blades a little bit - improving idle quality. Did I mention it helps the engine run cooler?

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