I am installing a Cold Fusion nitrous system (100 to 200 HP) and am wondering if I can use the PE spark advance to retard my timing. For example, if I put in -2', will it "subtract" timing or will I need to reduce the SA table to achieve the timing I need? I know it may seem like a "six of one-half dozen of the other thing", but I've got my timing curve like I want it and hope I can tweek the timing curve with the PE spark without changing the whole table. On the other hand, I have been considering a "drag strip" tune where I keep the timing lower across the LV8 range. I run a 5 speed and notice some timing retard induced by the momentary timing increase (and knock count) when in low LV8 during shifts. I thought I may also be able to fine tune the fuel with the PE tables for the nitrous injection. IOW if the jets for say 100 HP are set to give a rich mix, I could lean it out at the injectors rather than changing jets. Any thoughts?

I $8D the value is an 8 bit unsigned value of 0-255 pulled from the stack as a stored looked up value.
The SA values are all added together.
It will not accept a negative value since a negative would also represent values from 128 to 255. The -2 would actually end up being 253 and would add allot of spark Advance.
Not good in your situation.

Negative hex hurts my brain!

EBL supports N02. I never looked at it closely but there is more info on dynamicefi.com.

ronny, the ebl is controlling my n2o system, works like dream!!

Hmmm... glad I asked. Not working in hex so I'll let that dog sleep.

So, I should reduce my SA table by the max (say by 6' total) then add back in what I want via PE?

Or, should I zero out the PE spark advance and just put it all in the SA table?

Which also begs the question- What is the advantage of having PE spark advance over just plugging it in the main SA table??? An engine needs less advance during high and WOT conditions and more during light throttle conditions. Seems backwards to me. (then again I'm not trying to keep the EPA happy)

What do you think about having a drag-only program that doesn't have any (or very little) advance in the lower LV8 side. I'm getting a bit of spark retard (1-1.5 sometimes) during/after shifts (T5)?

Quote: So, I should reduce my SA table by the max (say by 6' total) then add back in what I want via PE?

I dont think that is quite right. I believe you will have a different need say at 75 map 3600 rpms while in PE vs cruising at that cell(way over speed limit!). Load may be the difference in SA. I understand PE fueling is an add on to the tables as is PE SA. One could assume at that MAP/RPM one would be in PE 95% of time but what of the 5%.

Quote: An engine needs less advance during high and WOT conditions and more during light throttle conditions. Seems backwards to me.

I think the difference is high load on motor may require PE fueling and accompanying PE SA.. Not sure on that though.

Do you have any knowledge of the vac assist on an old school distributor? I think my buddy disables it. I dont understand why. does it retard or advance under high vac(idle)? The theory should be the same???

I read a post a while back that explains spart timing as it relates to camshaft parameters. apparently the manufacturer can provide some info as to when the spark event should happen to maximize the cylinder pressure event occuring after TDC. Something of a window of opportunity or maybe begining of combustion event to end of measured in degrees that can vary on grind. I believe the example given was a window of 45 deg of crankshaft rotation for that application.

The vac advance system advances the spark under high vac condition; idle or cruise.
Racing dist have no vac advance; they are not looking for economy.
In old style dist , the spark advance is set by springs and weights which is what we are doing when we adjust SA.
We have the abilty to tune SA much finer than the mech setup.

I believe if you look closely at the GM vac "advance" dizzy you will find that under high vacuum conditions (idle, PT cruise), that it is actually vac "retard.

Difference of opinion! How can that be ! So the vac gizmo physically pulls the weights to a retard position? And the centrifical action of the weights advances the timing. So as the RPM's advance so does the timing. Is that consistent as to what the engine needs at WOT top maxed out speed?