Hey I have finally gotten my Ve table in pretty good now, and I seem to have lost some power?? Is it time to look at changing the Main spark table?? Im using a 7747 ecm with a AYUB bin that is apparently a leaded fuel export bin. I have changed that part but the main spark table only has 29 degrees of total advance at 3600rpm at 30map and it tapers of to 13* at 100 map?? this cant be good for perfomance?? Is there another spark table some where?? It is a pretty pathetic spark table I think. Any thoughts on this would be greatly appreciated.

 

yes, once you get VE close, its time to move to spark.
run no more timing than needed & watch the knock counts.
looking at a different bin for the same motor & trans as you have may give you an ideal on what you can do for spark. depending on your motor, i think you can bump 4 degrees across the board to start with, if you hear or see knock counts, back it off.
don't be surprised when your VE changes as you work on the spark table.

 

Ok thanks for the tip. Im wondering though can I smooth out the timing graph like I did the ve graph and not worry to much?? Im sure it needs more timing but I only plan on working slow at that part!

 

Maybe.

Some engines like a smooth curve, many don't.
Mine looks like the Rocky Mountains, but it works.
What you suggest *is* a place to start, though.

The best way, would be to measure what's happening in the combustion chamber while it's happening. Not everyone can do what I do, though..
Good dual trace scope, and it's not really that difficult, but does require an ability with a scope, and some electronics knowledge. Not much, but some.

The next best way, would be to pick a number, and performance test it.
Advance it, or retard it, a degree or three, and performance test it again.
Do this for each and every cell in the timing map.
Time consuming ? Yup. Work ? Yup. Work for the PE map, and other spark modifiers ? Yup, but it takes a whole lotta runs.

The worst way, is to advance the whole map a couple degrees until it knocks.
Back off the cells where it knocks 4 degrees, then advance the whole map 2 degrees
again. Repeat, until it's knocked in every cell, then back the whole thing off 2 degrees
or so. You'll have a "pretty good" knock limited map, which may, or may not, be the best performance map.
Back off the whole map another 2 degrees, and performance test again.
Then, repeat for temperature variations, baraometric pressure, humidity, etc.
Keep doing that until no further increase in performance can be had, or until you just get tired of it, which ever comes first. Might take a year or so. ( mine did )
Risk of damage ? Sure ! It's knocking, after all. Easy ? Yup. Work for the PE map, and other spark modifiers ? Nope. Things are changing too fast in PE and such.


OK, maybe that was the second worst.
The worst is to pick a number, because you just KNOW that's what the engine wants, and run that.

Having said that, I did do it the second worst way, because I didn't know any better.
Bought a few sets of plugs, fortunately didn't do any internal damage ( that I can detect ) other than burn away several platinum spark plug electrodes.
Got close, then went the scope route, and I'm not done.

Then, you go back and fix the VE tables, which have changed, then back to the spark tables, which have changed, then repeat.

Good thing we enjoy this sort of thing.

 

When you say "scope", are you talking about an ocilliscope? I cant figure a way this would help other than knowing the plug is sparking when its meant to. Is it possible or practical to explain what you mean? Thanks.

 

Yes, but it's faster, easier, and simpler to point you first at this link:
http://www.fs.isy.liu.se/%7Elarer/Projects/main.html
This explains the trace, which shows the spark, spark duration, flame formation, pressure rise in the chamber, and pressure drop as the piston starts down the bore.
That's what you're looking for. ( ultimately, and a simple scope shows it well )
Then, to tell you that the big issue is the power supply, and point you at this link:
http://www.google.com/patents?vid=US...zoom=4#PPA1,M1
particularly Figure 2.
Since mine has a dist. that's pretty close to what I'm doing.
In Fig. 2, part #18 is .05uf at 2KV, part #12 is 5 meg, part #14 is 100K. ( voltage divider to protect the scope )
Part #16 or 17 is a 1KV spark gap. It's purpose is to bypas the cap when the voltage
exceeds 1KV, and prevent the cap from blowing up. ( again )
Could be a zener, but I haven't found a cheap one that will withstand running very long.
Haven't tried a varistor, because I don't have any laying around.

The second trace of a dual trace I run from the reference pulse that goes into the ECM, so I'm referencing the same crank position ( within a degree or so ) as the ECM.
Sophisticated, yes, but elegant, simple, and effective.
The objective, is to put the pressure peak between 10 and 20 degrees after top center.
Your engine might want 13, or 17, but it'll be close to 15 ATDC in any case.
( at whatever spark advance causes that to happen consistantly )
That first link explains why, once you get within 3 or 4 degrees, further improvement is a fraction of a percent, and in my opinion, not worth chasing.
This stuff is all patented, so you can't sell it, but that doesn't mean you can't use it !

 

would not MPH be a definative test?

IOW run car at a certain RPM and MAP cell using your current SA table note the MPH and then bump 2-3 degrees and recheck MPH.

Would not MPH increase indicate more HP? Above assumes no knock develops.

 

Yes, absolutely, but as I posted above, takes a whole lotta runs !
( well, not the RPM part. Same RPM, same MPH. It's a gear thing, but I know where you were going )
Also takes the same conditions, temperature, humidity, tire pressure, wind direction and speed, driver consistancy, etc.
For me, getting the spark right is always the hardest part.

 

Wow, well once again, i appreciate this info, even though i have not been able to dig into it yet.. I see your in Akron, and im at school at the University of Akron right now actually.

Ive got the MAF setup, and have only played with the fueling parts so far. Spark advance does appear intimidating at first, mostly due to my lack of experience with it. But when i kicked up knock and then cringed when I looked at the big timing in the corvette ARAP bin, I decided ill go with reading and research over trial and error...

 

If you're at UA, you're less than 5 miles away, yes.
SA is intimidating, mostly because getting it right is so tough.
To much advance you buy internal parts.
Not enough, runs hot, and milage sucks. Might buy cats.
Between the two, it runs OK. Maybe not great.
That's why I ( and others ) have been searching so hard for a way to dynamicly determin optimum spark as its happening.
Unfortunately, the method I've settled on appears may be subject to the Heisenberg principal to some extent. Still, it's the best *I* found so far.