I'm not sure I've ever shared this file with the group. I made a spreadsheet to mimic the 3 components of spark advance; static, mechanical and vacuum. In my EFI setup I run two advance tables that are additive. One is based on static + mechanical, the other is vacuum.

In my spreadsheet I've taken the values from our manual and labeled them "spec" and highlighted in yellow. If I've extracted stock data correctly, the static advance is 15*, the mechanical advance goes from 0* to 20* starting at 1000 rpm and getting all in by 3000 rpm (actually this isn't actually stated, but seems to be consensus) and the vacuum advance goes from 20* to 0* from 15 in Mg down to 0 in Mg (manifold vacuum).

The model allows for you to change the shape of the mechanical advance curve by simulating either one or two springs in a distributor and the start/end RPMs that they work over (simulates spring stiffness). The vacuum advance is not adjustable and the curve is based on the manual data.

The stock setup DEACTIVATES the vacuum advance at idle through the use of the little micro switch on the throttle. I believe this is to prevent too much advance when cranking so that it isn't too difficult to start the car. But, that means at idle a stock car is at ~15* advance. If it weren't for this cutout, the advance would be 15* static plus another 20* vacuum since at idle the engine is creating the most vacuum. If you have your foot on the gas when cranking, does this make the timing immediately jump to 35*?

One question that begs asking is what is the optimal advance for idle? The theoretical answer is the one that creates the greatest manifold vacuum (lowest kPa numbers in Megasquirt) and that's what they recommend when tuning in Megasquirt. What values have you other EFI guys determined?

The model also lets you put in a maximum amount of advance. 15* + 20* + 20* = 55*. Does this sound too much for our stock engines? It would occur at high RPM throttle lift and deceleration. In a stock setup, the micro switch "pulls out" the 20* of vacuum advance, so I need to figure out how to model this.... Megasquirt has a decel fuel adjustment, but not one for spark timing. Practically speaking, just lowering vacuum advance values in higher RPM, higher vacuum areas of the table (lower right) does the trick.

I would love to look at some of your advance tables that you are running on your cars to see how my model compares to them. My goal has been to mimic the stock system based on the assumption that some good engineering went into making it as good as they could in the first place (maybe too much credit?). Given the 100% flexibility that software gives us, I'd like to tweek!

Comments? Please post tables so that I can compare. Thanks.

Megasquirt timing tool.xlsx