Ignition advance map help needed

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:
http://www.ptt.yu/korisnici/i/v/ivica/jolt/MegaJolt.jpg
Now, when it gets warmer I have to fit it to the car. I now need ignition map for my engine. I have default one that I can use, but since I converted to LPG only fuel I have to make my own map.
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:
http://www.ptt.yu/korisnici/i/v/ivica/edis/IgnitionMap.jpg
(ignore the orange and violet curves, gray is the one I am talking about).
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?
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Did the car run properly on the original distributor or is the LPG conversion going on at the same time as the Megajolt conversion? If it ran properly before, use a similar advance curve. You be better served looking for a resource that is more in line with LPG conversions...
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Nedavno Michael Yeager napisa:

It is running now on LPG and the original ignition system. MegaJolt conversion will (hopefully) allow me to tune the ignition for better performance and economy with LPG.
I am asking here how does original ignition work, so I can tune MegaJolt as best as I can. It looked strange that mechanical advance will retard few degrees past 3500 rpm. I thought that it is not the case, that it will advance up to a point and keep there up to the rev limit.
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In this case, I say start with the original curve and work from there. My suggestion is to look to an LPG group to find out how much tweaking you can do. I have no experience with LPG and my guess is not too many other people here do either. The retarding of the advance doesn't seem right to me either but....

I am interested and wish I could offer advice other than this.
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