</font><blockquote><font size="1" face="Verdana, Arial">quote:</font><hr /><font size="2" face="Verdana, Arial">Originally posted by johny1i:
<strong>I appreciate the suggestion, OldJeep, but I'll admit that the ported vs. manifold issue has perplexed me since I first heard it suggested. Enough so that I hooked up a vacuum gauge inline with the vacuum advance to record the vacuum pressure at 500, 1100, and 1600 rpm. For manifold (stock), it was 14.5", 16", and 16", respectively for those three RPM settings. However, for ported vacuum, it was 0" (at idle of course), 1", and 2.5". Therefore, it seemed to me that it would almost be like not even having vacuum advance hooked up on a ported setup until you get the engine rpm's up, and even then 2.5" doesn't come close to advancing the timing as much as 14-16" of vacuum do. I'm not saying that either way is wrong, I just don't see how the little vacuum advance mechanism on the side of the distributor can function with such a small amount of vacuum. (as you can tell, I'm a tinkerer when it comes to engines <img border="0" title="" alt="[Wink]" src="wink.gif" /> )</strong></font><hr /></blockquote><font size="2" face="Verdana, Arial">Weird - my manifold vacuum is 18" at idle and goes to zilch at W.O.T. I used to have a gauge in the dash - in fact some old cars had them as an option - the idea was to keep your foot out of it and keep the manifold vacuum up and the fuel mileage up as well.
Think about this - you want the distributor to advance in time with the engine rpm - manifold is at it's highest at idle, thus giving you full advance at idle..
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