DIY LTCC or similar system for LT1s

[spfautsch]

The first value is the BASE dwell. It is derived from the IGN vs rpm table.
It is multiplied with the coolant vs ign multiplier and than multiplied with the map multiplier.

The coolant scalar is a coolant value scaled for the table.

That was basically what I gathered from looking at the calibrations, minus the min / max value.

For me, the takeaway from looking at the factory dwell tables was:

1) the factory calibrations for all intents and purposes implement zero dwell compensation for MAP
2) they seem to be reducing dwell as rpm increases
3) temperature matters

A little research led me to this page [link] which contained some information I hadn't found previously.

I recalled from ee 101 30 years ago that temperature changed the resistance of copper but had long since forgotten the direction and magnitude.

Temperature will increase the resistance of the coil and wiring, ‘0.393 % per ºC’ is copper’s temperature characteristics so at 100 ºC its 39% higher, drivers actually have lower losses at higher temperature (semi-conductor materials used) and so help cancel out some of the temperature effect on losses.

And I assume this is why the GM cals are reducing dwell with rpm (though at a relatively marginal rate).

about 0.6 ms of spark time is sufficient at high engine speed for good combustion due to the excellent mixture formation in the cylinders.

I am really interested in a hot coil test.

As am I.

Which is why I ran all the tests I mentioned previously with the coils at room temperature (~21c) and then repeated after letting them let them sit in my oven at ~80c for a half hour. I didn't post any of that information because I really want to get a more complete picture at different voltages. But since you asked, here's what I observed.

data format: [dwell time in ms],[system voltage],[coil temp deg c]

D580 - dwell time before current limiting evident
4.5,12.8,21
5.0,12.8,80

D581 - dwell time before current limiting evident
4.6,12.8,21
5.2,12.8,80

D514a - dwell time before current limiting evident
5.3,12.8,21
7.3,12.8,80

8183 - dwell time before current limiting evident
3.6,12.8,21
3.8,12.8,80

D585 - dwell time before coil fires
5.0,12.8,21
6.0,12.8,80

This is compelling evidence that temperature compensation would be a good feature to add. But as always, there's a catch - depending on mounting location, underhood airflow conditions, etc. coolant temperature simply can't be relied on as an accurate representation of coil temperature.

... On that pcm I can change dwell via obd and can run some experiments with engine running. The code can be transferred to lt1 pcm and based on my calculation the pcm can run dwell upto 1.5-1.8ms at 6000+rpm without overlapping coils.

Again, I mean this in a light-hearted way, but I think you might have a patching addiction. Also, 1.5-1.8ms of dwell at 6000 rpm should quite clearly explain the stern way I'm going to answer the next question.

If you are willing to make a more close integration between LTCC and PCM we can setup dual mode.

I'm no more interested in discussing this than I was when you mentioned it previously. It seems very pointless. If you want to control dwell in real time you could more easily modify the controller code, or implement a feedback loop, etc. Integrating this into a 25 year old ecu via patches just seems like the wrong direction. But, as I shouldn't need to mention again the source is freely available. Fork your own version and call it something else if you so desire.

By the way, "LTCC" is a product of Bailey Engineering. Let's stop calling what we've done here that please. Lest a cease and desist letter arrive in my mailbox for something I'm doing in a non, or more accurately, "negative" profit manner.

... there are roughly 5 different types.

Part numbers make that list meaningful. Without them you open the door for assumptions to be made, which breaks the scientific method.

I found somewhere that aftermarket coils have some crappy igniters that can cause all kind of problems. I also found some reviews that running too much dwell

If you look hard enough you can find pretty much anything you (may or may not) want on the internet. Use much discretion in what you choose to believe, or believe nothing.

Let me jump off on a slight tangent here - and rant a bit. When I publish my test data I fully intend to disclose the source of the coils I tested. There is one that came in a Delphi box, but could easily be counterfeit. The rest are asian knock-offs with the exception of the 8183 coils which I hope are the genuine article, but were sold as "scratch and dent" and didn't come in original packaging. My point here is that I'm funding this adventure with my own money, and not one of you has made a monetary contribution to the project in any manner even after I've asked repeatedly to borrow coils to test. So while I'd like to be testing only the genuine article, they're goddamned expensive. Testing salvaged parts of unknown condition introduces another variable in the scientific method. So I've bought the cheapest stuff I can, because at some point the notion of spending money from my own personal toy budget is going to get sour. In fact, I'm starting to taste it now. Stepping off the soap box now.

What we might miss with the few dozen milliapms is that they might run the coils without the 430ohm resistor to limit the current. The igniter might be hungry for more amps if it is not limited.

I'm currently running 100 ohm resistors in place of the 470 in my car. I think I posted the igniter current at that configuration, but if I didn't I have it on paper somewhere. The difference was negligible, still well under 1 milliamp. So the 20ma number and "a few dozen" were clearly complete bullshit derived from non-scientific methods.

Did I mention that I managed to run the coil through a led and resistor. If we put leds on the circuit that might reduce the noise on the avr.

I wouldn't use an LED inline with a system critical circuit. LEDs are made to emit light, not protect the driver circuitry. Not to mention, you're going to create a huge voltage drop across them. There are no diodes inline in the ecu pics you shared, so I think you're inventing a fix for a problem that is imaginary until proven real.