I tried running my vaccume advance off of manifold vaccume and it kicked my idle up pretty high and everytime i put it in drive the dash would start vibrating and shaking, but i honestly could not tell a diffference in off idle or light throttle cruising power at all, in fact i made a run on manifold vaccume around my block and on ported vaccume and i swear it was running better on ported vaccume, but yes the manfold vaccume did give it better idle qaulity but other then that i think i will stick to ported vaccume.