DIY LTCC or similar system for LT1s

[kur4o]

Some quick update.

After I realized the suggested dwell is alittle too much to my taste and the overall soft feeling of the car, I build a new table from scratch, using some data from Gm calibration.

I fatten the cranking dwell around 8ms, and reduced all other areas to around 2-4 ms based on rpm and temp.

Did some very intense driving, putting the engine in any possible range you can imagine. What I didn`t test yet is heavy WOT with very rapid deceleration.

Overall no issues at all. Wot pulls finally behave like a real cop system. I looked at some old opti logs and compare the 60-125mph times.
The Coils on plug cut roughly 2.3 seconds and at high rpm shifting I can feel the trans is starting to have a very hard time to keep up with the extra torque.
SO FAR, THE BEST BOLT ON MOD I PUT ON THE CAR.

What else I noticed. ALmost any knock retard I got all the time during WOT pulls disappeared, the engine run much cooler on heavy pulls.

To get on the technical stuff. I would really like to test some interpolation between cells on table lookup.

What I also want to discuss is how the lt1 likes the spark. Bigger gap and longer spark duration or less gap and shorter spark duration.
If the cpu can handle it some initial multispark can also make wonders on fuel economy.
It will be something like that main spark, wait minimum amount of time[spark duration]charge 1-2ms second, discharge. It will be weaker spark for sure, so a faster coil is a must.

[spfautsch]

Glad things feel better - this makes me think these coils (and possibly all the "D" models) are getting 10-20% more dwell time than they need. Or in other words the dwell limiting which is what my tables are based on, only comes into play well past ideal dwell. Did your stuttering when blipping the revs up improve with more dwell or less?

When I get the dash buttoned up and can get mine back on the road I'll try to make some time to try some cell interpolation.

Multi-spark shouldn't add significant cpu overhead. Once I have some basic interpolation working I'll start thinking about the simplest way to implement it. Offhand it shouldn't be much of a challenge. I'm just not very optimistic because the OEMs aren't doing it (as far as I'm aware).

[Terminal_Crazy]

Overall no issues at all. Wot pulls finally behave like a real cop system. I looked at some old opti logs and compare the 60-125mph times.
The Coils on plug cut roughly 2.3 seconds and at high rpm shifting I can feel the trans is starting to have a very hard time to keep up with the extra torque.
SO FAR, THE BEST BOLT ON MOD I PUT ON THE CAR.

What else I noticed. ALmost any knock retard I got all the time during WOT pulls disappeared, the engine run much cooler on heavy pulls.

What level of power are you putting down?

TIA
Mitch

[kur4o]

What level of power are you putting down?

TIA
Mitch

Never really measured the output, Just standart stock engine with mods, cam, headers, CAI and other small pieces.
We can use the maf reading to calculate power, but again not sure how acurate is the reading of the maf..
On second wot pull, it reach 320g/s, I remember on first have seen upto 350g/s.


I think lt1 will highly benefit of multispark. Looking at GM they have multispark in code on all 2014+ pcms. Just the tables are zeroed for some reason. Coil not support or no real gain in emissions.

On our rough burning, inefficient combustions and AIR-fuel mixing LT1 engines, multispark might provide better as a secondary burning of what`s left in the cylinder.
Not sure how the coils will like it. That might be the reason GM drop it. Development of highly expensive, exotic coils with faster charging.

I also forget to mention that with beefed up crank dwell the starting feels much faster and healthier.
Still cant` assist for the slight miss on light rapid ,throttle application, I think I am having some fueling issue too. On heavy throttle application at idle, the sound and revving is brutal, compared to old opti revs.

Overcharging the coils definitely leads some other unknown variables into play, reducing total spark output. Some realtime control for the dwell, can gives us the minimum dwell the coils will start to miss, at least on idle and slight reving.

On my test mule with d580 coils I hack the pcm to command custom +- delta dwell to find the lowest you can go. Definitely some good dynamic data can be observed.

[Terminal_Crazy]

Thanks Kur4o.
It looks like an excellent upgrade.

[spfautsch]

kur4o your PMs are full again.

I think I might have mis-interpreted your most recent one.

On hard decel event after cruising, the spark advance drops from 40* to 2-3* and than when you apply throttle it jumps again to 40* in no time. I guess we need to take some logs to see if it affects controller to lag some 2-3 spark events.

It was also felt in car like sluggish pedal, not sure if it is fuel or spark, since the injectors are also cut out at that point.

After re-reading this I think I better understand what you're saying here. While I would still like a better explanation of what you're talking about with "lagging some 2-3 spark events", I have noticed that transitioning out of DFCO is somewhat abrupt. As I have no way to do an A : B comparison (diy-ltcc vs distributor), I can only suggest you try that to see if the sensation improves. Personally, when DFCO is active I know the injectors are off and I don't expect a smooth transition back to combustion versus air pump mode. But I've never heard a pop or perceived what I felt to be a misfire.

I finally got mine back together and ran it some today. It's been sitting for over a month so the passage of time makes the sensations all that more intense. It was refreshing to remember that when I'm cruising at 15-25 mph in 2nd gear, or 20-30 mph in 3rd gear, a quick stab at the accelerator reminds me that I need to lose about 25 lbs (as my beer gut and fat head get sucked into the seat). If there's any lag or sluggish pedal here, I'm not capable of perceiving it with my butt-dyno.

Anyway, I'm going to try to do some logging + testing this week to see what, if any interpolation is needed and other fine tuning tweaks. I'd also like to scratch a few items off the to-do list like time-based failover / limp mode and to finish an assembly + install manual and document what I learned back in December on voltage sensing accurizing.

[kur4o]

I make some indepth log analysis. Finding the biggest positive jump of about 16*. On high rpm converted to ms is not much and can be compensated. On very low rpm around 1000 it can be a little enough to be felt a bit, since it converts to something about 1.5ms reduction of dwell. I still needs to find the exact condition when this can happen and to fatten the dwell in that range.

Now on the decel conditions, the issue seems to be fueling. The dfco have some spark blending recovery, so you don`t get a 40* jump but slightly increasing the advance in couple of jumps of 3-5*.

Also plan to increase the high rpm dwell to compensate for the 2 inbuilt Gm timers. What do you suggest as the max on-off time in percent that will not decrement spark output. I am sure some visiual testing can be done on your rig, with different on-off settings for 5-10 minutes constant running.

Not sure if you can make some DYI pressure chamber. A thick plastic box with a thread for a spark plug and a hose for pumping some 10-16bar pressure.

[spfautsch]

Finding the biggest positive jump of about 16*. On high rpm converted to ms is not much and can be compensated. On very low rpm around 1000 it can be a little enough to be felt a bit, since it converts to something about 1.5ms reduction of dwell.

I'm thinking that instead of some table interpolation maybe a simple damping / smoothing function on the millseconds to degrees conversion would be better.

Now on the decel conditions, the issue seems to be fueling. The dfco have some spark blending recovery, so you don`t get a 40* jump but slightly increasing the advance in couple of jumps of 3-5*.

My morning test drive (haven't driven it in a month) seemed to agree. I have on occasion felt the fuel resume from DFCO present a bit of sluggishness. I do have some code in the profiling logic that can help determine whether it's missing a firing event or two in this scenario, but I'm not sure it's worth spending time on at this point in the project.

What do you suggest as the max on-off time in percent that will not decrement spark output. I am sure some visiual testing can be done on your rig, with different on-off settings for 5-10 minutes constant running.

I think 50% duty cycle is more than safe unless you're planning on trying to qualify for a NASCAR event where you're going to be running > 5000 rpm for several hours. But that's just my gut impression of how these coils work. A safer answer would be I don't have enough information to answer that question.

Not sure if you can make some DYI pressure chamber.

I'd love to build some more complete data for these coils, but I also have other projects I need to / would like to tackle. Fixing the rotten garage door trim, the bathroom windows, etc.

Anyway, I do have some good news. I just got back from the first of what I'm sure will be many test runs, and I think I reproduced your on/off issue with a hard WOT pull (no deceleration was involved). The issue continued on for a while just like you described. Felt more or less like a 2-step that had been left on after launch and was getting random, incorrect sensor data. At the first cross road I pulled off, shut it down and restarted, and the issue was no longer apparent. This tells me it's most likely some boneheaded picket-fence error (unchecked bounds) or something similar. I'll have to spend some time analyzing the logs, but it's probably something incredibly simple + stupid. That's not to say it won't be hard to find, but my fingers are crossed.

Also, I've been messing with fattening up the cranking dwell, and I think a 160 multiplier for the 100/200 rpm rows is already too much. Will post more observations after some experimentation.

[spfautsch]

I can feel the trans is starting to have a very hard time to keep up with the extra torque.

Another thing occurred to me just now. Having recently immersed myself in the 700r4 / 4l60 / 4l60e for the purpose of building / rebuilding the transmission in my wife's daily driver, I learned one particular tidbit that makes me want to caution you about excessive RPM or torque in first gear.

This transmission's primary weak point is the 3rd gear clutch and the fact that the check ball for the 3rd gear apply tapering tends to wear the valve body separator plate until it sticks itself into the hole and causes timing problems that make the 2-4 band eat the 3rd clutch pack with 4-3 shifts under power. You can change your trans fluid and filter every two weeks and still have this eat a high-mileage transmission.

The second biggest point of weakness, and the one you want to pay attention to with high RPM and / or torque is the sunshell that keys itself into the 2-4 drum. In first gear this very large and heavy assembly rotates at double crankshaft rpm (not accounting for torque converter loss). Without a beefier sunshell and / or 2-4 drum, the interlocking fingers can bend under the extreme centrifugal force to the point they cut into the transmission case. Similarly, healthy increases in torque can also fracture the splined drive collar completely off the sunshell, or strip it's splines off.

If you aren't big on learning how to rebuild an automatic transmission I would encourage you to tread lightly, particularly if you have sticky tires and modified shift pressures.

These transmissions can be built to withstand serious abuse with a hardened sunshell, 2-4 drum, and beefed up 3rd gear clutch pack. But I wouldn't spin the factory components past 10,000 RPM (5,000 at the crank / input shaft) under heavy torque conditions, particularly if they have a lot of miles on them.

[In-Tech]

The sunshell is a problem but as mentioned, that can't be fixed without a rebuild, among other things.
However, if inclined, you can drop the valve body and replace the steel balls with ceramic and a hardened separator plate.

[spfautsch]

The sunshell flaring out or fracturing is pretty much (completely) separate from the # 3 clutch apply check ball digging through the separator plate. Hard 2-1 downshifts are what I'm most concerned with in this particular instance.

Now that I've done it twice (complete rebuild) I'm not nearly as adverse to the 4l60e transmission. But its built to sustain a given amount of torque. Blast through that threshold with disregard, and you're going to pay the piper.

All that aside, I still love to select the gears without the computer trying to steer me in the EPA's prescribed direction.

I'm the king of hijacking threads, but let's please get back to the topic at hand.