Vacuum Advance - Manifold or Ported

[cobrashoch]

Depends, I've done it both ways on custom engines. Inside the dist. vacumn curves (initial advance) are one of those tuning things you do to set a engine up, along with jetting a carb, and setting a advance curve. When I fire a new one up I use no vacumn and retard the dist. a bit just for safety. After things are going a bit I usially start some of the tuning stuff to bring her in. Most times after things have settled down I end up using the maifold full vacumn because it's typically more consistant on low vac. engines, but you will have to play with springs, programs or such. There are many factors to look at but I typically ask a guy how are you going to use the car/engine, and that determines how it's really done. I know this is no help but that's the way it usially gets done, it's a tuning thing and it depends on the type of engine you have.
cobrashock

[blueovalfanatic]

Interesting thread, and I can see both points. I myself would aim towards ported vac. for distributor advance, but the manifold vac. point is intriguing. I also have to say that Cobrashochs' point is both interesting and valid. Would it make a difference that was noticeable by "seat of the pants" method- quite possibly not, but I also think a properly set-up and tuned engine runs much deeper than only what you can feel and sense.

I'm looking forward to more opinions and questions. One, say you were running a pretty steep cam- if your power brakes were suffering enough, would a distributor on manifold vac. make it even worse? It seems it would have to. Not really a question, but more of a consideration. I have wondered why someone would eliminate the vac. advance all together, but I guess it just depends on the situation.

Greg