DIY LTCC or similar system for LT1s

[vilefly]

I found the LTCC installation instructions here. https://www.camaroz28.com/forums/lt1...ns-new-882760/

I noticed it requires the EST signal to function, as well as hi/low res signals. If it truly controls dwell by itself, then it would have no need for the EST signal at all. It probably takes the EST signal, measures the pulsewidth and stores it, multiplexes a pulse to the correct ignition coil driver and fires the coil at a stock pulsewidth/dwell time.

If I had to, at gunpoint, reduce the dwell time, I would send +300v to the primary of the ignition coils. Works for MSD. Or maybe just 24v. Lie once, cheat twice.

Oh, something else the LTCC unit does......flash codes with green light to identify failure conditions. Seems to complain if the key is toggled inside of 5 seconds for some reason. This is what I have been able to find out so far.

[spfautsch]

If it truly controls dwell by itself, then it would have no need for the EST signal at all.

EST being the white wire? Are you implying the LTCC module has it's own spark advance tables?

Adding a buck-boost circuit to power the coils with > 14.4v adds part count and would significantly increase cost. Considering this and the difficulties I see in writing the controller firmware, the LTCC module seems very reasonably priced. I may just buy one eventually but right now my toy fund is severely depleted.

If I had a way to produce a cad drawing of the trigger wheel quickly I'd draw up some graphics to illustrate. But I just don't have time. Here's the best I can do with words.

Let's assume some generic constants - 5ms coil charge time, and 30 degreees spark advance. 1000RPM idle and 6000RPM wot with these same constants. Please double-check my math.

RPM            1000        6000
Crank Rev. Time (360d)    60ms        10ms
Cam Angular Velocity    0.333ms/d    0.0556ms/d
Cam deg - 5ms dwell    15 deg        90 deg
Spark advance in ms    4.995ms        0.834ms
Cyl 1 Dwell Strt (cam)    30d btdc    105d btdc
Cyl 1 Dwell Strt (crnk)    60d btdc    210d btdc

What I'm hoping you take from this is that at 6000 rpm the #1 coil pack will need to start charging 15 cam degrees before the #2 low res slot is encountered, or approximately the same time the #2 coil is fired. And 30 degrees advance at 6k rpm is fairly tame at 100kpa.

This has been a very valuable learning experience. I've learned that the factory coil must have really low impedance and charge time. At the same time I can't help but think I'm probably losing power above 5500 rpm due to weak spark.

[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.