A nice vacuum advance article

[Faron]

Sadly Tom most don't realize two important  things with aftermarket Dist's , First they need to be re-curved ( mechanically ) along with the vac adv , BUT most aftermarket Vac adv are NOT adjustable ,With Most you can limit the total , but usually they come in too early and add too much , the companies will SELL you one to replace the NON adjustable unit , or you can get one from a knowledgeable person  ,A Tip = if the Vac adv does not have flats going around the tapered part of the canister it is NOT adjustable and most are finding out it runs BETTER with it NOT used , They HAVE the potential , just not  Out of the Box 

[chris401]

EDIT: I am not recommending anyone to set there vacuum advance that high on an older engine. Too much will put your spark into the next cylinder at the wrong time. With modern engines other factors such as being 4 cylinder, 6 cylinder, camshaft and fuel timing are involved.


While watching PID values in modern autos I have noticed spark advance being in the 60's under cruise throttle. I get everything past the lean burn comment. Maybe he misspoke or left out a word or two, or too proud to correct his post? I think he meant the cylinder temp stays hotter longer on a lean burn, quicker temperature flash and cool on a rich burn. If he is a legitimate engineer communication and humility are not common skill sets.