What I meant to say was that the vacuum advance will retard at wot due to insufficient vacuum to operate it, not that it won't operate at high rpm. According to my manuals a vacuum advance requires about 3.6 inches of vacuum to operate, at wot the average engine drops to about 2.3 inches. As i stated earlier though, I don't have a vacuum advance, only mechanical, and my truck runs great without it. No detonation, and I have plenty of power through the entire rpm range. I do admit that this thread has me thinking that I need to bone up on this subject more, I have an ASE recertification test on engine performance coming up later this year.
