I am in a process of fitting distributerless ignition in my '87 BMW 316 (1.6 M10 engine). I finished assembling MegaJolt ignition control unit:
I wanted to use original ignition curve (initial + mechanical), so I checked my Bentley BMW E30 manual, and there is a table with total advance (but I think that this is just initial + mechanical advance) at different rpm. So I draw a diagram with the data from the table:
It is interesting to see that ignition advance retards after 3500 rpm. I wonder why (and how) do BMW make their distributors to do that.
My question is is this correct ignition curve? Should I use it as a basis for further modification by adding advance based on a load (vacuum)? Any idea how much (~8 deg)? And do I add the same value at idle, mid-range and at max rev?