Great post using real world examples of the pro's con's of using ported vs manifold vacuum! Any time you are at WOT or heavy throttle you esentially equalize the pressure above and below the throttle plates. It does not matter where you have the vacuum advance hooked up for WOT operation, neither one is adding any additional timing.
You may want to record how much additional timing is being added by the vacuum advance. By the description given I would suspect you are adding in near 20 degrees accounting for the negative impact at idle when using a manifold source. Few "high performance" engines require much over about 8-14 degrees of additional timing during light throttle operation. I know some folks who use none without any ill effects. For engines prepared here about 8-10 degrees is added for a slight increase in fuel economy for part throttle cruising. A ported source is used on all but bone stock late model stuff.....Cliff
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73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
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