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Posted by Chris Case @ San Diego on Friday, February 29, 2008 at 21:00:08 :
In Reply to: Re: There is no vacuum at WOT. posted by John Dunn on Friday, February 29, 2008 at 16:42:11 :
Then, if the throttle does open past the port, it acts like a normal vacuum advance. It's called 'ported vacuum' rather than 'manifold vacuum'.
Hey, that's an example of how much good a vacuum unit does. Ever noticed how they will raise the idle speed as you connect it to intake vacuum? That is exactly how much 'free power' you gain by runing a vacuum unit.
It's also why they use 'ported spark'- the port system maintains a lower idle speed. To keep the engine cooler when idling for long periods ?