Natesully

I was wondering if there are any good guides around on spark advance tuning? I see SD/MAF info stickied right above, and I've tuned fuel on quite a few Megasquirt setups, but how exactly people dial in timing remains a mystery to me.

I understand doing dyno pulls and adding/removing spark to find MBT, and avoiding detonation - but how do you tune the cruise/light load areas of the map without an actual loading dyno?

Natesully

Well, just found this thread: https://ls1tech.com/forums/pcm-diagn...rtia-dyno.html

I guess the answer is you use a loading dyno, or you guess. I suppose I should find somewhere near Austin that has a loading dyno once I start changing things and need professional tuning.

redtan

iTrader: (5)

Not a perfect way, but you can tune of manifold pressure. You want the lowest possible kPa reading while cruising, so if you do back to back tests on the same road you can find out what timing produces the most vacuum.

jimmyblue

iTrader: (11)

I won't claim this is right or best, but it's given me agreeable
behavior.

First, you have to clean the knock retard behavior. Double
the decay and halve the fast attack rate. This keeps a KR
event from persisting longer and jumping up higher than it
should, for data quality reasons.

Then, you drive around and look at the knock retard
histogram after a while. Wherever you find KR (look at the
"max" view), subtract a degree and wherever you didn't,
add a degree. Repeat and repeat again. Eventually you
will have a histogram all full of 1 degree KR or nothing.
You are now up against ping timing across the board.

Now subtract 2-3 degrees from everywhere (or what
number you believe is the difference between MBT and
ping-onset; I found 2 degrees in some old technical
paper, once, and stuck with it.

If I were you I'd then copy to the low octane table and
subtract at least 2 more, there, so you have some
margin and protection for aging, drift etc.

Now if you do this under ideal conditions, you will want
to return to this exercise on a day with hot nasty air,
and this time put your effort into tweaking the IAT
retard adder / multiplier tables. You probably don't
want to pull timing from idle / cranking but definitely
at cruise and upward you will need to deal with bad
air since you've done squoze all the sand out of GM's
sandbagged tune.

Min-MAP is a good goal for cruise efficiency. A co-pilot
twiddling real time controls (spark advance) as you go
rolling along, can help you find the happy place in one
outing. But you could do it yourself iteratively.