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Thread: DIY LTCC or similar system for LT1s

  1. #796
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by kur4o View Post
    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.

  2. #797
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    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.
    -Carl

  3. #798
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    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.

  4. #799
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    Thanks Kur4o.
    It looks like an excellent upgrade.
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  5. #800
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    kur4o your PMs are full again.

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

    Quote Originally Posted by kur4o
    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.

  6. #801
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    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.

  7. #802
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    Quote Originally Posted by kur4o View Post
    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.

    Quote Originally Posted by kur4o View Post
    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.

    Quote Originally Posted by kur4o View Post
    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.

    Quote Originally Posted by kur4o View Post
    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.

  8. #803
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    This should be worth a laugh or two. Didn't have a chance to analyze the logs yesterday afternoon, dug in just now and found the issue straight away.

    Code:
    [runtime],[rpm_index],[volt_index],[ect_index],[map_index],[dwell_ms],[dwell_multiplier]
    533,8,7,11,7,3.33,120
    534,10,6,11,6,3.76,119
    534,11,7,11,6,3.27,118
    535,15,6,11,15,4.05,128
    535,21,6,11,15,3.96,125
    536,24,5,11,13,4.19,113
    536,25,5,11,14,4.19,113
    537,201,6,11,0,4.65,147 < unchecked bounds returned from the rpm index function gives unknown dwell multiplier
    537,201,6,11,17,3.54,112
    538,201,6,11,17,3.54,112
    538,201,6,11,17,3.54,112
    539,201,5,11,17,4.16,112
    539,201,5,11,17,4.16,112
    540,201,5,11,0,5.46,147
    540,201,5,11,15,4.75,128
    541,201,5,11,14,0.04,1 < multiplier lookup likely getting data from a changing location in ram. this was causing the on / off sensation
    541,201,5,11,15,4.75,128
    542,201,5,11,0,5.46,147
    542,201,5,11,0,5.46,147
    543,201,6,11,9,6.36,201
    543,201,6,11,0,4.65,147
    544,201,6,11,0,4.65,147
    544,201,6,11,0,4.65,147
    545,201,6,11,2,0.03,1
    545,201,5,11,13,8.28,223
    Stupid mistake made when condensing and modularizing the table index lookup functions.

    I'll have a fixed, sweep tested version ready soon. In the mean time just don't spin your engine past 6800 rpm. Edit, make that 6600 rpm.

  9. #804
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    Found and fixed improperly handled array bounds logic in all three table lookup routines that could have impacted any min/max transition adversely. Sweep test framework has been added as a conditional. Somewhat embarrassed to have put this out for consumption by the general public, but then again it's code that makes a v8 run to beyond 6500 rpm without a mechanical distributor and it cost you nothing to download.

    Drove the fixes home over my normal 63 mile "back roads" route and the butt-dyno was not disappointed. Idle seems to be slightly more stable and overall torque was more authoritative / bordering on brutal in the mid-2000 rpm range.

    Planning to add a dwell base adjustment - thinking "-" globally decreases the map vs rpm multiplier table, and "+" increases it. So ten "-"s fed into the uart would adjust the base multiplier from 128 to 118 and vice versa.

    Will try to get this ready for public consumption early next week.

  10. #805
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    0.9.43 tested, sig updated with link.

    Disclaimer - I was not able to test above 6600 rpm in-car because I didn't want to come to a complete stop and shift into 1st. Next time I'll wait until 80mph in 2nd to let off. But I'm fairly certain the fixes will resolve any unwanted behavior.

    Also added in this version (quite some time ago) is a 5.xxx volt constant in config.h for fine-tuning voltage sensing. kur4o if you have a 7-18v variable dc power supply and a lab quality multimeter, fine-tuning this to the nearest millivolt (3rd decimal place) gives best precision. If not, the default value will put you close enough.

    The multiplier offset seems to work, though I've been unable to push it far enough to see an increase in map / decrease in responsiveness. This lets the user increase or decrease the entire map vs rpm multiplier table by a fixed positive or negative number. It resets to zero with loss of power.

    After giving it some thought, it wouldn't be impossible to turn this into self-tuning routine that could find ideal dwell in cruising ranges, though it would require some damned careful steady-state driving.

  11. #806
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    Just wanted to update with more info. Fully tested to 6800 rev limiter, no abhorrent behavior.

    Also, I tested the multiplier offset fairly extensively. Based on your observations (kur4o) I decided to lower dwell to the point I could sense a difference in idle. It didn't happen until about -84 (base multiplier 44) or about 70% [edit: below] of the test data "max" dwell target. Somewhere in the neighborhood of 1.1ms. Even drove on interstate @ 75mph as low as -78. I ended up scaling the 8183 dwell table by 0.6 across the board, and adding some minor tweaks to the map vs rpm multiplier table. Seems to put the average dwell target around 2.0ms in normal driving.

    I put about 150 miles on this setup with another 50 already on the trip odometer since last fill-up and came out at 22.1 mpg even with several hard wot pulls, a 1/4 mile pass to 130-ish and 6-8 aggressive merges onto interstate (15-75mph @ 60-90% throttle). No noticeable change other than feeling some "surginess" around 1700-2400 rpm occasionally that seems to be a product of using too many floating point logging pids at 500ms intervals.

    kur4o if you've got time I'd love to hear your impressions of using the multiplier offset and how the engine reacts to less / more overall dwell. I'd really like to figure out if it's possible to use one map vs rpm multiplier table or not. Though if I have to I can probably just buy a complete set of D514a coils. Maybe a set of D585s too. Though I'd really rather spend that money on paint and fixing the dying window regulator motor.

    I'd also like to discuss some ideas for implementing multi-spark - i.e. what type of tables would make the most sense, when it should be disabled, etc. Obviously it will have to work within lower rpm ranges, based on coil charge / recovery time.

    Meanwhile I'll try to plug away at the documentation. Have I mentioned how much I hate writing documentation?

  12. #807
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    I really hope to test the update soon. It does sound really promising. WIth the possibility to dial on the fly some offset and test wot times with fatter and leaner dwell.
    It also opened the door to some auto tune logic if there is enough cpu power, finding the best dwell, not sure what we can use for feedback.

    I think the current table setup is workable enough and gives some edge over the traditional GM tables design. You will likely loose some rpm vs volts spread but within the usable 11-15 volts it is pretty acceptable.

    Finding the weak points that can`t be worked out can gives us a better idea which coils will work best on the broader range. ANyway it is some hack job of very old technology and not all can be perfect.

    For the multispark. We might need minimum off time scalar. The time the coil discharges. To take advantage we might just disable on rpm threshold, where the minimum 1.5 dwell at least cant be reloaded fast enough to give a spark before the piston reaches bottom.

    We also need to find where will be the best time in degrees to apply the second spark. Something like an EOIT target but for dwell. I guess some realtime control for second spark delivery can gives us an invaluable feedback what needs to be done.

    I will take a look at what is designed by gm and hopefully get some fresh ideas.

  13. #808
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    Quote Originally Posted by kur4o View Post
    ... WIth the possibility to dial on the fly some offset and test wot times with fatter and leaner dwell.
    While I'd love to hear your feedback, if your transmission is struggling to deal with the torque you might want to lay off the WOT passes.

    Quote Originally Posted by kur4o View Post
    I will take a look at what is designed by gm (on the subject of multispark) and hopefully get some fresh ideas.
    Sounds good.

    I think the auto-tune idea may be premature. Unless / until misfire detection can be made to work reliably, I don't think there's enough feedback with only MAP info. Still, being able to adjust dwell on-the-fly was eye opening. I would have never thought to take more than 50% of the maximum dwell out in order to see / feel a change.

    Will continue to focus my energy on documentation, time based (limp home) run mode, and misfire detection, in that order. I'm also pretty sure I'm going to go ahead and acquire a set of D514a and D585 coils to use for testing with my own butt-dyno.

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