Originally Posted by yragat
Your advice is always right on and appreciated!
According to all the old manuals I have the Caddy distributor only has 8 degrees of centrifugal built into it,so if I set it to have say 34 total then initial would be 26??????
You have to verify how much mechanical advance the distributor supplies. Same thing for the vacuum advance.
If the distributor is limited to a small amount of mechanical advance, the vacuum advance most likely will be giving a lot of advance. This is not needed, an adjustable vacuum advance is needed for the best results.
There's no way to know what the best initial timing setting is for an engine (especially one that has had the cam changed to a performance grind) until you have worked your way up from a safe setting. You will know when you're too far advanced on the initial timing when the engine is hard to start hot, or runs on when shut off, or pings when accelerating hard from a low RPM.
That said, starting out at 14-16 degrees BTDC of initial timing is a starting point you can work from. If the engine will start hot, and not ping, and not diesel when shut off w/the initial set at 26 degrees, then you can run it that way- but I doubt it will want that much advance.
So if the distributor doesn't give enough mechanical advance (meaning 26 degrees of initial is too much), the slot of the advance plate can be lengthened a bit at a time to increase the mechanical advance to give you the amount of mechanical you need to go w/the initial advance that you found to work best from your previous testing.
Once that's all worked out, add the vacuum advance back in by reconnecting the hose. You can try both ported and manifold vacuum, there is no way to know which will work best w/the cam you have until you try it both ways. Manifold vacuum is most often recommended, but if the initial is set high enough, adding more timing at idle by using manifold vacuum to the vacuum advance can over advance the engine at idle.