the physical position of the distributor is set to 8*. the initial spark advance in the constants table in tunercat is set at 0*. what would happen to the main spark table if you changed the constant to 8* from 0*? would all of the values in the spark table increase by 8*? I am trying to determine the physical timing vs the ecm timing.

With the distributor set to 8* and the BIN initial timing set to 0*, this adds 8* of timing across the board.

If you change the BIN constant to 8*, which matches the distributor timing, there will be 8* less timing across the board.

When both match (which they actually should), the values as a wash. Meaning that the ECM subtracts out the initial constant, and the distributor adds it back in. Which makes the main SA table WYSIWYG. Unless the ECM/Mask you are using has a bias value for the main SA table. . . Confusing.

RBob.

thank you , as the old saying goes 'clear as mudd'...... what you said is what i though but i get confused and some time read too much into it. I am using a 1227727 and the main spark bias constant is 9.8*. then does this put 9.8* back in to the spark advance table?

With a bias of 9.8* the SA table entries are actually 9.8* less then shown. Unless you are using an editor and definition file that takes into account the bias value. If so then the spark table is back to WYSIWYG.

I take it you are not running the $8D mask?

The purpose of a spark table bias is so that timing can be less then 0 degrees.

RBob.

I started with the $42 and AMUR; I have a 355 sbc'454 TB with 91# injectors, Summit K-1103 cam stock intake and exhaust' ported 126 casting heads with I=1.96 E=1.50 .imported the AZFT9503 accel enrichment vs diff map and AE vs diff tps tables and zeroed the retard tables. I have been tuning the VE so that i have BLMs in the 120-129 range. thought it about time to start on the timing but am having trouble getting an understanding on how to do it and what it all means. I know that i can really screw things up ($$$) and cant aford that. I have read that you increase timing untill you get knocks and then back off a couple of degrees but how many are ok?would I bump the timing table up 2* at a time until i record knocks and then back off or by individual cells? or by block of cells? what would you do?

In the DIY_PROM board tuning Guide sticky, chapter 5, under sub-chapter: 8063/7747/8746

Is a write up on SA Logic. That will explain how the timing is calculated in the 1227747 ECM.

You can only do the advance until knock then back off if the heads are detonation limited. Otherwise the power will drop off and the engine will get rough when there is too much SA timing.

RBob.

I went to the links that you recommended and have read them. it will take me a while for my old brain to to figure out what it all means, decypher it and apply it to my application. thanks for your help........Rivers

I think it is more than my pea size brain can decipher. the spark bias thing is what I do not understand. If I understand it correctly with the dist and initial spark constant at 8* and a spark bias of 9.8* (which was in the bcc i used) the values in the SA table are 9.8* less than shown? Why would I wast this? What problems would I create for myself if I just zeroed the bias table and removed 9.8* from the SA table and started to fine tune the spark till it knocked and then backed off a degree or two so no knocks were logged? R.
RBOB I do not think you saw my reply