I am still tuning on my 350. I am trying to get the best performance possible for street use. I am trying now 8* btdc with about 14* of advance from manifold vacuum.I have tried 14* initial with about 14* vacuum advance. Both idle about the same. With the second option I would need to limit mech. advance to 18* (told 32* max with vortecs, I have to figure out how to do this ) Does it really matter where your advance comes from as long as the total is in line with your combo? Performance wise its very difficult to tell if 1 or the other is better other than going to the track I suppose.Either way it idles nice and has good street manors although performance from idle seems a bit lacking.When I was tuning the demon carb a while back I had everything out of whack (carb settings) and the ole girl went like stink, but didn't idle worth a darn.

Jerry ....for my stuff always had best results on sbc with vacuum 10-12*, 8-12* initial and tune with crank degrees yes your Vortec's wont need that much inital .. IMO it does matter but I don't have much Vortec experience do asearch here and also find his website Daves smallbody hei's he certainly is one person that could help you lot's of experience ..he has done dist for some here and I have one of his now for my BBC FWIW

you can't add in your vacume advance to the total because it falls off as the throttle is reaching wide open. Your initial plus mechanical is your total timing. Vacume is more for fuel economy-(burning a lean mixture at cruize speed-part throttle) Tune you combo without any vacume then add vacume advance a little at a time to see what she likes. Most aftermarket vacume advance has an adjustable limiter.

with your current combination of 8 initial and 18 mechanical you only have a total of 26 at wide open throttle.