[bobcowan]

I used to have an excellent article that discusses this, but now I can't find it. Maybe some one else can find it.

Base timing is predominantly determined by the cam shaft. Bigger cams need more base timing. I'm using a cam with .248* intake duration at .050" (.304 advertised). I use 18* as base timing. The article recommended a range in that area.

The second factor is engine vacuume. When you're in that area, use a manifold vacuum gauge. Set base timing where vacuum is the highest.

SBF's do best with total timing somewhere around 36*-38*. BBF's do best with a little bit less, like 32-34*. You want it all in by 2,500-3,000.

Vacuume advance should put 8-10* additional timing when vacuum is high - idle, low thottle cruising. But that's something you'll have to play with until it feels right. You don't want detonation when you tip in the throttle to climb a small hill.

For a street car, I bleieve in keeping timing very conservative. You might pick up 10hp with an additional 4* of mechanical advance. But what happens on a hot day? Or if you get a tank full of mediocre gas? Now you have detonation that will break the pistons. For peace of mnd and longevity, keep it conservative.