DIY LTCC or similar system for LT1s

[kur4o]

That`s it. Ltcc measures the time between low res pulses and calculates rpm. Than use simple lookup table [rpm] vs [low res pulses till BTDC] to start charging the coil.

low res pulses till BTDC=at tdc counter is reset for current cylinder and you have 7 low res pulses till next ignition event.

Here are some formula [60*1000] / [x*4]=rpm
60=60 seconds in a minute
1000= to convert in ms
x= time for 90* cranshaft rotation or time between low res pulses
4= to get 1 crankshaft revolution time

2.5ms/90 = 0.0278ms for 1 degree rotation at 6000 rpm

46 total advance = 1.27ms error at 6000 rpm for dwell time. which is acceptable since dwell can vary.
Since nobody runs anything between 20 and 38 at high rpm that error can be brought down.

[vilefly]

spfautsch,
I am not sure if the LTCC unit has its own spark tables, but it has its own spark-retard tables and settings. I cannot say if it changes timing during normal, non-knock operation without proof for myself. I grant you it would be cheaper not to bother with it.
But it seems rather certain that it does not control dwell time, only divides it by 8 by selecting coils. If you take the stock dwell time, and give each coil 2 revolutions before the next fire, you will have solved any dwell problems easily without the need to modify anything. Now, you can magically rev beyond stock speeds. Cheap and easy.
As to the lack of power above 5500, that depends if you are using a stock cam or not, or outrunning your injector flow rate/on-time. I don't know any specifics on the engine you mention, unless it is the one listed under each of your posts. The science of dwell time is no mystery to me, but it never hurts to review. Injector on time can pose major problems at high speed, though.

[spfautsch]

That`s it. Ltcc measures the time between low res pulses and calculates rpm.

Don't you think measuring / tracking spark advance would be necessary also?

I am not sure if the LTCC unit has its own spark tables

I'm more than a little sure it doesn't. More directly the ECM controls spark advance, which is why it requires a signal from EST. Otherwise anyone with a LTCC would have to customize the spark tables for their own tune.

If you take the stock dwell time, and give each coil 2 revolutions before the next fire, you will have solved any dwell problems easily without the need to modify anything.

You also create a condition where you have a bunch of coils that are energized all the time and will all spark simultaneously the moment the ignition circuit is cut.

On top of this, wouldn't coil overheating be a concern?

[edit: or did I misunderstand your suggestion here]

As to the lack of power above 5500, ... The science of dwell time is no mystery to me, but it never hurts to review. Injector on time can pose major problems at high speed, though.

The point I was trying to make is that the stock setup has very little dwell time capacity at higher RPMs and spark advance. Or am I mistaken?

The only way I can forsee doing something like this "easily" with an Arduino compatible uc would rely heavily on the high-res signal, using dwell lookup tables and keeping everything in terms of degrees so the uc can track by the high-res count. Unfortunately it still needs to be able to measure the time between low res pulses to four or five decimal places or RPM [edit: and spark advance] calculations are going to be horribly inaccurate. So three inputs that all need relatively precise and fast ISRs, and time to within 100us, possibly 10us. All this is well outside my comfort zone.

Attached is the sketch as I left it yesterday. It has not been tested but does compile. If it's of any help take whatever liberties you'd like with it.

[kur4o]

Here are some threads with pictures.

https://www.youtube.com/watch?v=_8JrLEso7Vg at 0:56

http://www.dw-zone.com/ltcc/LTCC1.jpg

So ltcc have different board revisions.

https://encrypted-tbn0.gstatic.com/i...mWbfWgxK6HQx-X

And the delteq unit.

[spfautsch]

I recognize that microcontroller package but it's from waaaaaay before my time (in the realm of ucs).

I think before I jump to any more conclusions I'd like to see a scope capture of the following signals.

EST
LowRes Opti
Inductive clamp on #1 spark
#8 Injector (or #4 or whichever gives best waveform capture for kur4o's request)

Both at idle and holding at say, 4000rpm.

If that's not something you can do any time soon vilefly, I'll look into doing it. I wouldn't mind owning one of the little capture devices you posted, even though my toy fund is currently deep in the red.

[vilefly]

"You also create a condition where you have a bunch of coils that are energized all the time and will all spark simultaneously the moment the ignition circuit is cut.
On top of this, wouldn't coil overheating be a concern?"

Naw. You're just overthinking it like I did earlier. All I meant was that the on/off signal for the stock, single coil would be rotated through the 8 coils in sequence. None of them would be on until the transistor was switched on by the redirected EST signal. This would be plenty of charge time for a coil running 12.5% as much as the original coil. This is the basis of my non-processor approach to the problem. Just GATE the signals to the right coils at the right time. No calculation. No changes. Just sequence the gating so that it "arms" the right coil transistor at the right time. I have no intentions of going beyond this. You have plans to do so, I bet, and there's nothing wrong with running 2 arduinos to accomplish what you need to do. One to calculate, one to act on it. 2 arduino pro minis don't take up much space. (5v-16mhz versions) I don't know for sure if it would be fast enough, but at $5 each, it would be nice.

I have weekends off from work, and away from the best scopes. I have only 1 old 4 channel Interro PDA scope with a small black/white lcd display. Probably have to take a picture with my phone to get a decent capture. Or.....I could try for the next work week when I have access to everything. Either way, I will see what I can do.

[spfautsch]

All I meant was that the on/off signal for the stock, single coil would be rotated through the 8 coils in sequence. None of them would be on until the transistor was switched on by the redirected EST signal. This would be plenty of charge time for a coil running 12.5% as much as the original coil.

This makes the assumption that the LS coils have electromagnetic properties that are similar to the Opti / HEI2 coil, and I think that's a flawed assumption. If you recall back to this post the auto companies put a lot of effort into sourcing the cheapest components that will get the job done. I'm sure the LS coil selection received the same due diligence. If they knew they had two full engine revolutions to provide adequate charge time I'd bet that heavily influenced the type of coil that was chosen. I haven't been able to find any specs on the HEI2 coil or driver module to compare, but what I was hoping to see with the waveform capture at idle and then 4k rpm is a rough picture of dwell at different speeds. I would imagine there's a dwell table in $EE but I haven't had a chance to dig through all the .xdfs and the disassembly looking for it.

This is the basis of my non-processor approach to the problem. Just GATE the signals to the right coils at the right time. No calculation. No changes. Just sequence the gating so that it "arms" the right coil transistor at the right time. I have no intentions of going beyond this.

And that approach might be perfectly adequate up to a certain RPM. But I doubt many of the LT-1 enthusiasts would care much for an ignition system that performs worse than a properly functioning Opti.

You have plans to do so, I bet, and there's nothing wrong with running 2 arduinos to accomplish what you need to do.

I haven't ruled out the possibility but it's certainly looking more and more like a scenario where the the LTCC module is a much better value than what I initially thought. The only thing I would gain by spending all the time and effort to do it on an arduino platform is having the code open-sourced.

In looking for more intelligence on the subject I ran across this article that seems to hint the opti system is heavily reliant on the high res signal for controlling spark advance in real time during cranking when angular velocity is least stable. There's even a heading where they discuss time versus angle based ignition.