I need info/help on how to generate an advance curve with MAP, Going all in! Options

[Dr Evil]

I have a few advance curves to consider for my distributorless ignition system, but all of them are for the mechanical aspect only without consideration for manifold air pressure (vacuum).

Where do I find a chart or info on MAP affect on the advance?

If no chart/data, how do I generate such a set of data points?

Which advance curve should I use for a 2.7 with SC cams?

The following is all I have to go off of:

[DNHunt]

I'm not sure how much this will help you but, the ignition map I got from Jake from my four was derived from his work with the Mallory dizzy on his 4s. He used a very simple curve with 12 degrees advance at idle to a max of 28 degrees at 2800 rpms. It would look even simpler than the first curve you have because the rate of advance vs rpms is steady. That distributor is pretty accurate but it is still a big compromise. With programmable ignition you can do much more so the map he sent was a lot more complicated.

First he added more total advance in the mid rpms which puts a single hump in the curve similar to the 2 humps in the SC curve. There is also some advance taken out at high rpms to compensate for the high piston speeds in my engine. Next there is some retard of the curve at high manifold atmospheric pressure (lower vacuum, the throttle plate is letting more air and load is higher) to avoid misfires. Finally there is more advance in areas of the map where manifold pressure is lower (higher vacuum, throttle plate closed or cracked a little).

Remember that the advance numbers are relative to where the sensor is. Whatever correction there is for the sensor and missing tooth relative to TDC has to be accounted for in the software or in the values in the map.

I'd start with one of the curves and put the values in the graph in the cells on the map in an area where the engine is under moderate load. Then I'd add a couple of degrees in the mid rpms and back out a couple at high rpms. This curve just gets repeated in the cells above and below with the exception that it slightly flattened above the first set of entries and more exaggerrated below. to compensate for air pressure changes.

Pay attention to cylinder temps and listen for pinging and adjust. It's probably best to start a little retarded and add advance.

Dave

[DNHunt]

This is a quess. Consider it a mental exercise and an attempt to give you a visual of what I found on my /4. If you decide to run it (I wouldn't without confirmation of people with a whole lot more experience than me) and you hole a piston remember this. Docs want wiggle room.

I played with the 911E curve you posted. This is what I would start with but, it's just a guess on my part. I'd sure try to get hold of TimT. I bet he'd have more answers and better ones too. Remember I've never messed with a /6 so take this for exactly what it's worth (similar value as lectures on phlebotomy in medieval medicine and care of the common cold, taken to the patient it probably won't hurt them but, it's probably not going to make them better either.)

Several things to consider here! I added a little extra advance in the midrange rpms because I would guess the stock dizzy probably compromises here I added a small bump at 500 rpm's to help recover from a stumble at idle. I retarded the timing under load. I advanced the timing on overrun. And I took a little advance out at very high rpm's.

[Dr Evil]

Hey Dave, thanks for the info. I am heading out of town so I am not able to digest this stuff in entirety. I have some questions and will post when I get home.
Thanks again! (IMG:style_emoticons/default/thumb3d.gif)

[TimT]

Didnt you just ask this question a few weeks ago? (IMG:style_emoticons/default/confused24.gif)

[Dr Evil]

It is possibel that I did ask this or a similar question, but I assure you that I was not as clear as I needed to be. For the next 2 weeks I can wrap my head around this problem where as before I had med school stuff to contend with and that makes one forget much of what they knew. I am hoping to make this thread as direct and action packed as possible. I have posted what I have so far, which is arguably incomplete.

I know I was asking about timing, but I did not know enough about the MJLJ programming to ask questions correctly (getting better, I hope).

[fiid]

There is an excellent thread on this topic on the Megasquirt board:
I think someone built an openoffice spreadsheet that does it to - scroll through and read carefully (IMG:style_emoticons/default/smile.gif)

http://www.msefi.com/forums/viewtopic.php?t=9941

[Dr Evil]

Dave and Fiid,
the info you guys posted is spot on and a great starting point for me. I will post my progress as it happens. I just picked up a laptop with win98 on it so I can try to program my MJLJ.

I found the other posts that are related to this so I will link these to the main MJLJ thread that I started for ease of archiving. Some info is repeated, sorry for that btu I am trying ot learn something complicated in the middle of med school which is daunting at best.