how much does the distributor advance under load/acceleration?
Supreme Member
Joined: Aug 1999
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From: College Station, Tex USA
Car: 89rs
Engine: 400Sb
Transmission: Tremec 3550
there is on one answer to this question. I think everything after 86 had basically a hollow distributor and all of the advance was controlled by the ecm. If the distributor is aftermarket, or a standard hei, the vacuum advance varies from 10 to 15 degrees on some models. mechanical advance is probably limited to about 15.
Supreme Member
Joined: Jul 1999
Posts: 18,457
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From: Loveland, OH, US
Car: 4
Engine: 6
Transmission: 5
A typical performance spark curve might start out with 10 or 12° of static timing; at 1500 RPM or so, it begins to advance centrifugally, which adds more advance that gradually increases up to 15° or so at 2500 RPM or thereabouts; if the engine is under no load (cruising) the vacuum advance typically adds about 10° more on top of all that. So the maximum advance would be something in the 35-38° range. Every engine/ car/ trans/ gear /driver /gasoline /altitude /air temp combo is different, so no one curve will be "ideal" for all situations. For that reason I always get a kick out of people who think that there's some "magic number" they can set their timing to, including the factory spec.
The vacuum advance goes away under load, not the other way around. When the vacuum is high, the mixture in the cylinder is very thin, and lean besides; so it takes longer to burn; so in order to get maximum efficiency, the burning has to be started sooner.
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"So many Mustangs, so little time..."
The vacuum advance goes away under load, not the other way around. When the vacuum is high, the mixture in the cylinder is very thin, and lean besides; so it takes longer to burn; so in order to get maximum efficiency, the burning has to be started sooner.
------------------
"So many Mustangs, so little time..."
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