Ignition advance map help needed

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Yvan - 25 Jan 2008 17:32 GMT

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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Michael Yeager - 25 Jan 2008 19:56 GMT

>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:
[quoted text clipped - 22 lines]
>(vacuum)? Any idea how much (~8 deg)? And do I add the same value at
>idle, mid-range and at max rev?

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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Yvan - 25 Jan 2008 20:25 GMT

Nedavno Michael Yeager napisa:

> 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...

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.

Signature

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/__/ / \ ** Registrovani korisnik Linuksa #291606 **
/ / \/ /\ \ ** Registered Linux user #291606 **
/__/\____/--\__\ ** http://counter.li.org/ **

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Michael Yeager - 27 Jan 2008 00:49 GMT

>Nedavno Michael Yeager napisa:
>
[quoted text clipped - 6 lines]
>conversion will (hopefully) allow me to tune the ignition for better
>performance and economy with LPG.

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 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.

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

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