spark advance curve modification

[Dave Zug]

Dig wrote:
> 
> > I have a turbo car (8.7:1 compression, 91 octane required) with a GMP4
> > ECM. I KNOW where the spark curves are on the eeprom, my question is:
> >
> > can someone give a description of a baseline tequnique i can use to
> > modify the spark table for "mild/medium" performance increase?
> 
> What kind of a powerplant is it? (4-cyl, v6, ?) I do some chip twiddling
> on a 4.3 turbo V6... (GMP-4)


V6.. 3.1 litre intercooled. boy have I been looking for *you*


> 
> > example: increase advance for the lower load lines 1-2 defress, and the
> > upper load lines 3-4 deg,  or increase beginning of all lines 1 degree,
> > middle of lines 2-3 degrees and ends of lines 1-2 degrees..
> 
> Let me preface this by saying that the following assumes you have an
> increased fuel capacity or better octane or better intercooling (or
> all the above)...

I *WOULD* be able to give more boost electronicly IF i could fing the 20 psi boost limit 
setting. I also would be able to give more fuel if i knew fuel table location. As it 
stands, I use 94 octane and have an adjustable wastegate rod tuned for 19-20 max on cool 
day. i often get injector lockout in cool fog. The wastegate is effectively delayed a 
shord duration allowing boost to build quickly at low rpm's.. i'd like to return the 
adjuster rod to factory spec and use fuel/boost tables to get performance. the GPP4 is the 
latest gm puts out, i think its "711". the cal-pak is double chup, one for ESC(nut eprom, 
a formed circuit with 8 of the 28 pins connected. the 2nd chip is a 27c256 eprom, main 
code starts at 2000 relative(A000 absolute) spark table is around 0108 relative or 
thereabouts. checksum routine is at or near ffe3(absolute) or so, end of chip. i give 
these references so you can see any similarities between my chip and yours.. i really 
would like to know those table locations!!!
 


> 
> Your timing table is set up as an absolute MAP vs. RPM vs. timing, no?
> With a turbo, you'll want to add more timing at low MAP (~100 KPA abs.)
> and low RPM (600-2000) to get the turbo to spool up a little quicker.
> Avoid big jumps at high load (170-180 KPA abs.), you'll end up getting
> a lot of detonation.
> 

yes, MAP. ok, i see. an initial increase of adding 1 degree to first 2 data, then 1-2 deg 
addition to next 3 settings, 3 deg to next 2, 2 deg to next 4 and 1 to remaining, as a 
general guide for starters. i'll watch knock signal for increases. thanks.


> A lot of this tuning is best done by adding timing slowly, and watching
> to see what effect this will have on knock retard. Keep in mind that shifts
> in ambient temp will effect this dramatically, you'll see much more knock
> on a hot day.

if i overtune and get excessive knock on hot day, but dont want to (or can't) change chip, 
will an octane booster help temporarily?

> 
> I'd try to bump up the ESC attack rate for the testing period, so that if
> knock does occur, timing will be taken out quickly. Might also want to
> bump up the max retard parameter to allow more timing to be taken out.

again.. table/data locations?!?!
can you send a copy of a dump of your 4.3 GMP4? i'd gladly trade you for mine, i guarantee 
that *NO* "performance" chip maker makes one for me, 2 months research, and is the reason 
for me getting into this! glad i did.

> 
> Personally, I'm of the mind that performance increases should be acheived
> via increased boost and *decreased* timing. It's tough to determine where
> the decreased timing will hurt you more than the increased boost gains you,
> however.

point taken. limiting factor for me is that pesky injector shutdown routine at 20 psi! 
plus the boost being CONTROLLED to 15 psi.

> 
> 
> > engine is MAP controlled, not MAF and HAS ELECTRONIC SPARK CONTROL with
> > knock sensor.. can i rely in knock sensor to protect against possible
> > over-advance on eeprom if i accidently use a "FA" insted of "2A" ?
> 
> As long as you keep a close eye on knock retard during your test runs,
> you should be ok. You'll hit the max retard limit set in your ECM, which
> should tell you that you've got a little too much timing somewhere.

got it.

> 
> Do you have a 2-bar MAP, or a 3-bar? What's the service # on your ECM?
> 
> Dig
> dig at syclone.cc.und.nodak.edu


i have the factory unit from GM. i have seen items referencing a "better" map sensor, have 
not investigated details.

Looks like you can help a poor information-starved tech-hobbiest like me out alot! 
anything you can offer would be great!

the car is an 89 grand prix turbo. it can be seen in detail at:
http://www.ssnet.com/~advpower/dzug/89gpturbo.html

check it out and send a feedback form from there if you want.

click on the driver's door TURBO emblem to see another "hidden" car.

thanks for the time!