[Jcrotts]

I have been thinking about how to set up timing control and I wanted input on an idea.

Is it possible to use my current distributor with a speeduino board to simulate vacuum advance? Keep the centrifugal advance, but implement the vacuum advance based on map input, with the speeduino changing ignition timing based on vacuum, and the distributor advancing based on rpm. Is it possible to set an ignition curve that will not be thrown off by the varying position input, or is this not possible with the way ignition timing is calculated?

I have an electronic pickup in the distributor that will give 4 pulses. I know it's not the optimum setup, I'm more interested in will it work functionaly with the programing than what would work better. I'm not looking to squeeze out every ounce of performance, just trying to make it run reliably.

Just an idea, would appreciate some input.

[PSIG]

My first answer, is yes, it is possible to only apply "vacuum advance" to an existing curve. The ECM does not know that the timing has shifted (it assumes it is always at a fixed point set by Trigger Angle), and will apply however you tell it. As it does not know the actual timing, you can not see the actual timing applied - only what you add.

So my second answer is no, that would not be recommended, and preference would be to have the ECM control all timing functions in a coordinated manner. If you're doing some, you may as well do all, and you'll be able to not only see it real-time but also alter the base curve for maximum benefit. Mechanical curves are rarely the best timing, being limited by their function. IMO, lock the distributor and set TA so the ECM really does reference the crank angle, and dial it in.

If wanting to use the existing stock spec curve, you can convert the data into a stock table equivalent as a baseline. I did a multi-post about how this can be done in TunerStudio here: Creating a stock-equivalent Spark Table from factory service manual specifications