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Old 05-02-2011, 10:55 AM   #12
gearmesh, inc.
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Quote:
Originally Posted by Kwiksilver View Post
I don't really understand that. Isn't all the timing in by then anyway? I have been sold on using manifold vacuum and when the vac drops the timing would retard for pulling out of a bog. Does ported vacuum drop at high rpm's?
Ported vacuum starts to come on when the edge of throttle butterfly starts to rise above its port just above idle position. You will have to hook a vacuum gauge up to your ported port and go for a ride to see just how the vacuum signal from your port acts at various rpms and throttle openings. Generally, ported vacuum drops off the more you have the throttle opened, but has a tendency to increase slightly if at all as rpms go up. Vacuum advance was originally implemented to add some advance during light throttle openings just above idle for increased fuel mileage.
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