I was just informed that full manifold vacuum means that advance will fall away under part throttle acceleration. So who ever ran full manifold?

Guy who helped me build my engine was all about full manifold. He said thats how all the guys ran their cars in the 70's. That he never used ported.

Why was full manifold ever used then? How did they make up for the vacuum drop off for part throttle acceleration?

 

I run my vacume advance to manifold vacume. I can get the best idle out of it that way. I haven't noticed any problems with the vacume drop.

 

Spark advance will fall away under part throttle acceleration whether using manifold or ported vacuum.

The difference is at idle and throttle angles less than where ported vacuum comes on, straight manifold vacuum allows for more advance here.

Search for a recent posted article on this same topic, it includes the p/n for a vacuum can that pulls in full advance at only 8" vacuum.