[dmjlambert]

Hi, yes, from information gathering and learning standpoint, I believe I have it. Thanks very much for the education.

I have a stock distributor with a stock amount of vacuum advance (a lot). The initial timing is set more advanced than stock, to the highest BTDC I can go while preventing knocking. This allows for efficient and easy starting with no kickback, and adequate idle and mid-throttle economy and performance. At wide open throttle, my timing is not sufficiently advanced for high performance and efficiency. This is because the timing is retarded by the vacuum advance can. The timing curve is set up for conservative stock performance and maximum engine safety.

I have the vacuum advance running on manifold vacuum. My engine works equally well on ported or manifold vacuum, it doesn't seem to make any significant difference except when switching from one port to the other I need to adjust idle speed. And it only affects the engine at idle. So, I'm not convinced it makes any big difference which to use. My logic leads me to choose manifold because it just burns more of the gas in the cylinder before sending it to the exhaust, and therefore must be more efficient. I don't have an A.I.R. system or EGR, so nothing is going to happen with any unburned gas on my engine, except going out the tailpipe. Therefore, I can't find a reason to retard the timing at idle by using ported vacuum.

I will probably get into hot rodding this HEI at some point, or at least mapping the curve so I know what I have for future reference. I can't tell when because I have my interior cab work to do and A/C to get going, shock installation and other maintenance to work on. In 1969 there was no starter brace, and I don't want to start breaking things, so I want to add the brace before messing with the timing curve.

The guy who put in my exhaust put in glass packs, so I want to work on correcting that annoyance fairly soon, too. He asked what kind of tone I want, and I told him "no tone at all, I don't want to be able to tell the engine is running." Apparently to him that means glass packs welded in. I was mad, but just wanted to get the truck out of there and back to my side of Texas. I've now had a couple of years of listening to it every day, so it is getting old. Like everything on my truck I need to do it twice, that is my curse. That kind of stuff slows down my progress.