[wilkin250r]

I've heard arguments both ways for the ported vs manifold vacuum debate. I've heard some claim the manifold vacuum causes overheating at idle, I've heard some claim that ported vacuum causes overheating.

Most technical articles (not forum debates) will claim the ported vacuum was an attempt to improve emissions by increased exhaust temperature, but it comes at a price. The theory being that with the delayed spark, the fuel/air was still burning as it left the combustion chamber, past the valves, and out the headers. That extra heat improved the performance of catalytic converters and other emmission-reduction methods (with the obvious side effects of increased risk of burning valves and warping heads)

I know all of my carbureted engines seem to run best off manifold vacuum.