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Thread: What should I do about my main spark table?

  1. #1
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    What should I do about my main spark table?

    79 Jeep, AMC 401, 6197427, 454 throttle body, $OE, Tunerpro RT, Iron heads, 91 octane fuel, ~9.5:1 compression, forged pistons, Mechanical advance is welded, vacuum advance removed, .

    I have my computer controlling my timing and it seems to be working correctly. I have installed a 454 knock sensor into the side of my block and wired it up. I do not get a check engine light for my KS unless I unhook it so I assume it is working correctly. My Jeep runs pretty well but is a bit gutless toward the top end.

    Took it out for a run today, and logged my data. I had no knock retard ANYWHERE in my history tables. Literally, it was all 0's. I also did not hear any knocking/pinging while I was driving it. This made me assume I have no knock and intended to add 2 to 4 degrees to my table when I got home. But as I looked at my average timing table I see there were times when I was at almost 44 degrees! (here's my history table from TunerPro)
    Spark history.jpg
    If I compare the history table to the main spark table, the truck seems to be doing what it is supposed to: (here is my main spark table from my BIN)
    main spart table.jpg

    So I'm stuck. Do I go after my knock sensor assuming it is not working? Do I just assume, with 91 octane it will not knock, and take some timing out of it and see how it performs? Or do I keep adding spark until I get problems? Or am I missing something all together?

  2. #2
    Super Moderator dave w's Avatar
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    There is the option of temporarily disabling the Knock Sensor to compare the history tables, with knock sensor and without knock sensor.

    Possibly tap on the block, near the knock sensor, with a small hammer (vehicle in park at or near idle RPM's) and see if the history table records any knock retard.

    It would be a good plan to look at knock counts in the exported data log, aka .csv Excel spreadsheet.

    dave w

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    Good idea! I’ll try that out this week and post up my results.

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    OK, I rapped on it with a hammer and it looks like I got a little knock retard.

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    OK, I rapped on it with a hammer and it looks like I got a little knock retard. Not nearly as much as I would expect though.

  6. #6
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    There are at least 5 knock sensors for that computer. V-6, 305 manual trans, 305 auto trans, 350/454 manual trans and 350/454 auto trans. Being a different block completely you will have to see which one is more accurate in your block. Then there is also the knock sensor circuitry in your memcal
    Last edited by In-Tech; 05-22-2020 at 11:23 PM.
    -Carl

  7. #7
    Carb and Points!
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    Only a newbie, but I know the frequency of the knock 'sound' is related to bore size, and computer input is electronically filtered to listen to that particular frequency for knock detection.
    I'll leave it up to you to determine if that's of relevance here.

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    Rather than start a new thread, I will hit this one. First my original issues WAS:
    When I first started my truck tuning adventures, I did not have a knock sensor so I disabled all the timing retard capability by setting the "minimum temperature for knock retard" to 151C in my BIN, and promptly forgot about it. I also had retarded a bunch of the timing table because it looked like too much timing. Luckily I keep a log with every change I make to my BINs so during a look back over my notes, I saw it, put it back to 35C and added 4 degress of timing to the whole table. Now that I turned it back on, I not only have knock counts, I have timing being retarded the way it is supposed to!!! WOOO HOOO!!!

    MY QUESTION NOW, THOUGH:
    I have done a tuning run with my timing tables and have data on my knock retard. Do I just take that Knock retard number (running avergage), subtract it from the value in the timing tables, install new table in my truck, rinse, and repeat? Am I looking for 0's or just less than say .5? Is it really that easy to tune timing? I feel like I am over simplifying it...

  9. #9
    Super Moderator dave w's Avatar
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    Usually spark changes of 1 or 2 degrees will change the knock retard averages. It can be challenging to reduce knock retard, because increasing or decreasing Spark Advance will affect knock retard averages. Sometimes adding Spark Advance will eliminate knock retard averages, which seems counter-intuitive.

    dave w

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    Copy that. When I was trying to see why my knock sensor was not reading, I added a bunch of timing to my tables. I started with 454 tables and having an over square engine, I need more then 454. So I think I am in the ball park.

  11. #11
    Carb and Points!
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    Quote Originally Posted by dave w View Post
    Usually spark changes of 1 or 2 degrees will change the knock retard averages. It can be challenging to reduce knock retard, because increasing or decreasing Spark Advance will affect knock retard averages. Sometimes adding Spark Advance will eliminate knock retard averages, which seems counter-intuitive.

    dave w
    Pardon for butting in, but I've just started playing with tuning LS1, and spark seems harder to tune than fuel, at the moment.
    Dave W, would it be fair to say that having the tune take timing out due to knock detect costs you more performance than not having quite enough advance and no knock in the first place?
    I base that on observation from logging. I have a 'test dyno' bit of road that I log acceleration from 2 to 5 000 rpm in 3rd gear on, and use time scale to measure performance, quicker the better.
    Obviously no correction for airtemp, barometric etc, but pretty indicative, and 'real world' conditions.
    I am assuming more advance is more power, but upon reflection of that, maybe that's not true.
    And am I placing too much faith in my test method, as well?
    Again, sorry for jumping in, not wanting to hijack your post rang-a-stang.
    Last edited by Mr Weston; 07-03-2020 at 09:59 AM.

  12. #12
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    You're good Mr Weston (not hi-jacking at all). This is all information I am hoping to discuss.

    My understanding from reading other threads on timing is most folks will continue to add timing until they get high knock counts and retard, then back the cell(s) down just a tad. There is a finite point where there is too much timing. We want the max timing possible but as soon as we hit knock, we are losing efficiency (obviously there is knock from other conditions besides timing but for this conversation we are speaking purely of timing).

  13. #13
    Carb and Points!
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    Thanks for the info, rang-a-stang.
    Whilst having a think about it, another thing I remembered was that you're most likely to get knock at max torque, and I've seen that in my logging.
    Seems I can add more down low, and no knock,but not so much around 4000 rpm in my LS1.

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    MY QUESTION NOW, THOUGH:
    I have done a tuning run with my timing tables and have data on my knock retard. Do I just take that Knock retard number (running avergage), subtract it from the value in the timing tables, install new table in my truck, rinse, and repeat? Am I looking for 0's or just less than say .5? Is it really that easy to tune timing? I feel like I am over simplifying it...
    Knock is an audible event which indicates combustion pressure and temperature have risen too quickly and the energy which would be used to drive the piston is being converted into sound. Knocking can be caused by pre-igniton (before spark plug fires) or detonation (after spark plug fires). Triggers can include hot spots on the cylinder head or piston, lean air/fuel mixture, incorrect spark timing, incorrect octane rating, or a mix. During knocking the engine block, cylinder head, and piston top are heated above average temperature. As chamber temperature rises it becomes easier to light the air/fuel mix and the rate at which combustion occurs decreases. If knocking is allowed to continue there will almost always be damage.

    Preventing engine damage using knock counts is really a dynamic process. Once knock begins the computer has to reduce spark advance below the value where it first occurred. Timing might be safe to 43 degrees, knock begins at 44 degrees, then the knock sensor activity causes timing to drop to 39 degrees before knock stops. This is because the combustion chamber and piston top require time to cool off. A stock timing table and ESC system are programmed to advance spark to table maximum, and if knock occurs ESC will reduce advance until knock stops. It will then increase advance toward table maximum. If knock occurs during this process ESC will begin the cycle again.

    Tuning with knock counts imo requires time travel. Tuning with knock counts is not simply a matter of reducing spark advance at the RPM and MAP where knock is occurring. The goal is really to prevent knock by decreasing timing by the smallest amount necessary. Properly tuning with knock counts IMO requires reading datalogs from a point in time prior to the onset of knock to the point which indicates combustion chamber heating is causing or strongly contributing to knock. Changes such as afr increasing or rapid spark advance can begin a cycle of temp rise that results in abnormal combustion. I have seen cases where increasing fuel delivery at 2000 rpm prevents up to 6 degrees of spark reduction at 3000 rpm. I use the shape of the spark table as a guide. If I see a nice curve that generally seems to work, but requires a substantial change in shape (up to 4-5 degrees of timing reduction in one area) due to knock, I try to find a way to prevent knock in the first place.

    In short: Drive the vehicle to obtain logs. Review logs for knock. Adjust timing tables to reduce advance and drive again. If you find you are reducing knock by more than three degrees in any three adjacent cells review the logs for changes that can be made elsewhere which could prevent heat in the combustion chamber from causing knock.

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    Perfect!!!!! Exactly the info I needed! Thank you!!!

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