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Dead Parrot · 09-15-2018, 08:56 PM

Vacuum advance is only a part throttle thing. Assuming a daily driver street setup, part throttle is a leaner mix at lower cylinder pressure due to the high vacuum which burns slower and needs to be lit earlier. As you put your foot into it, vacuum goes down, cylinder pressure rises, burn rate speeds up but vacuum advance is less now because of lower vacuum so the fire get lit later.

Adjust your mechanical first to be full in at 3000~3500 and then worry about vacuum advance if it pings at part throttle.

There are several articles on timing and the 50+ advance at part throttle is what you want, again assuming a relatively normal street engine.

There are also charts on the various AC vacuum pots available and when they come in and how much.

09-15-2018, 08:56 PM	#4
Dead Parrot Registered User Join Date: Aug 2012 Location: Oklahoma City, OK Posts: 2,490	Re: Need Help With Timing Curve (I have Numbers) Vacuum advance is only a part throttle thing. Assuming a daily driver street setup, part throttle is a leaner mix at lower cylinder pressure due to the high vacuum which burns slower and needs to be lit earlier. As you put your foot into it, vacuum goes down, cylinder pressure rises, burn rate speeds up but vacuum advance is less now because of lower vacuum so the fire get lit later. Adjust your mechanical first to be full in at 3000~3500 and then worry about vacuum advance if it pings at part throttle. There are several articles on timing and the 50+ advance at part throttle is what you want, again assuming a relatively normal street engine. There are also charts on the various AC vacuum pots available and when they come in and how much.