2 replies to this topic

[CdnAustinAmerica]

I have a 123 tune+ distributor and I'm not sure how to program its vacuum advance curve for it, seems hard to find an example based on how they measure vacuum with the MAP sensor in it, I attached a pic of something I got from a lucas curve and halved the timing values for and converted to Kpa but it doesn't seem right?

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Edited by CdnAustinAmerica, 10 May 2025 - 05:43 PM.

[Spider]

The standard mechanic unit holds its advance beyond the point when it's full advance is reach, ie in your table and graph there once it reaches station 6, 7⁰ it will flat line there not go back to 0⁰.

The other thing, if I am reading that right, is there would be the highest advance at 0 kPa Absolute and that would taper off to max lowest advance at (in your case here) 47 kPa.

[crock]

This is what I start with for an A series engine, using crankshaft degrees, at -4 psi vacuum you are at zero advance, and at -8 psi vacuum you are at full vacuum advance of 10 degrees. Somewhere there is a book that shows Lucas vacuum advance curves for many of the distributors. Maybe someone remembers it and can post it again. My recommended total mechanical advance at wide open throttle is 32 degrees and this should be all in around 3000-3500 rpm. These are all figures to start with, to get better performance you need to test or find a real expert like AC Dodd.