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Thread: Custom E67 LS3 tune in 71 Chevelle

  1. #1
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    Custom E67 LS3 tune in 71 Chevelle

    Been tuning a GM crate LS3 with a mild TSP cam (225/330/114LSA)
    and 1-7/8" long tubes. It has the card style LS3 MAF in a 4" tube.
    Speartech made the harness. My transmission is a built 4L65E. My
    issue is with the returning to idle. When I drop the gas too quickly,
    the
    engine will drop to 400RPM and nearly die before recovering. Been
    struggling with this for about 6 months trying different things and
    nothing really helps keep it from dropping so far down rpm wise. I
    did the EQ/VE tuning and got it perfectly dialed in with a wideband.
    Same with the MAF tuning...its great and the MAF is screened with
    a honeycomb and has a nice smooth response curve. Car runs great
    all around except it tries to die out when you release gas too quickly
    in or out of gear. I tried adjusting the throttle follower torque by
    looking at other sample tunes to no avail. I try to resolve issues on
    my own and have come a long way but this one is testing me.
    I will try to attach my tune.

    Thanks.

  2. #2
    Advanced Tuner ProTools4's Avatar
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    -were are you located?
    -what did you do for suspension and brakes?
    NotoriouSS TAD
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    J5 - 96' Impala SS - 4700lb autocross machine
    Langston - 96' Caprice 9C1 Beater
    Rosie - 67' El Co - race truck w/ plates
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  3. #3
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    I am in Calera, Alabama. I am running C6Z06 brakes
    ATX tall spindles, Helwig tubular sway bars and bilstein
    shocks, a Lee Saginaw 670 series 12:7 box.

    Quote Originally Posted by ProTools4 View Post
    -were are you located?
    -what did you do for suspension and brakes?
    Last edited by gmachala404; 06-10-2012 at 11:30 AM.

  4. #4
    Advanced Tuner Shrek's Avatar
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    Quote Originally Posted by gmachala404 View Post
    ... tuning a GM crate LS3 with a mild TSP cam (225/230/114LSA) and 1-7/8" long tubes. It has the card style LS3 MAF in a 4" tube ... transmission is a built 4L65E ... issue is with the returning to idle. When I drop the gas too quickly, the engine will drop to 400RPM and nearly die before recovering ... did the EQ/VE tuning and got it perfectly dialed in with a wideband ... same with the MAF tuning ...
    If your VE / MAF tuning is accurate, then it could be an idle airflow issue. Attached is a PDF of the Final Idle Airflow values for an LS3 I tuned - it had a similar cam to the one you listed, but had a manual trans.

    If this helps, use it as a starting point, as the auto trans you have will need a slightly different airflow.

  5. #5
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    Thanks for the numbers. Those numbers are huge compared to mine. Whats your idle airlow multiplier vs ECT look like? I attached both of mine

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    I played around with the throttle follower step up and down tables and
    it has improved. The plunge back down to idle is slower and it seems
    to stabilize better. However, I am not sure what these two tables are
    doing. Pedal position vs airflow doesn't seem like it would do anything
    to rpm decay rate. Why can't there be just a simple table called
    RPM decay rate LOL. Don't know if I am on right track or not and
    looking at a bunch of sample files I don't see anyone modifying these
    two tables so I have nothing to go on but guessing.

  7. #7
    Advanced Tuner Shrek's Avatar
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    Quote Originally Posted by gmachala404 View Post
    Thanks for the numbers. Those numbers are huge compared to mine. Whats your idle airflow multiplier vs ECT look like? I attached both of mine
    These tables are in different units. The one you posted is in lb/min, the PDF I posted is in grams/ sec. For idle tuning I use metric units. The difference between the two is not of the magnitude you are thinking - perhaps only 10% to 20% (depending on the cell).

    My idle airflow multiplier vs ECT is similar to yours at operating temperature, but a little less than yours at low ECT.

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    Ahh yeah that makes sense I converted to g/sec and bumped my
    airflow minimum number up closer to yours. I used the other
    settings for step up and step down posted above then ran it for
    a while from a cold start. It died a few times when I first cranked
    it but it always does that after I flash a new tune. Then took
    it for a drive. It seems to do much better now. Time will tell
    I tried with and without A/C and it didn't die out at the usual
    spots. Time will tell. Its like having a hot girlfriend, its kind of
    unpredictable! Thanks.
    Last edited by gmachala404; 06-10-2012 at 10:24 PM.

  9. #9
    Advanced Tuner Shrek's Avatar
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    Glad to hear increasing the airflow helped. The E38 / E67 are very good at controlling idle (even with a large cam) if the airflow is correct.

    I generally monitor RPM, airflow, throttle blade position, and spark advance - to help find the correct idle airflow. If the throttle blade hangs when you get off the accelerator - you don't have enough airflow. If it immediately drops to idle position you may have too much airflow.

    The spark advance should also stabilize once the idle airflow is correct. I like to see spark advance in the range of 14 degrees +/- 2 degrees (at idle).

  10. #10
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    Thought I followup with the latest on this tune in case others have similar problems. I did a log of speed, rpm, tps and timing. I noticed as I rolled (with foot off the gas) to a stop the TCC cuts off at about 35MPH that's when the idle would plunge and stall. Looking at my logs I could see timing dropping right before the plunge. I never noticed the brake coast timing tables before as I was looking at the idle timing tables. And there it was in the brake coast timing table 10 degrees of timing instead of about 14 in the idle spark table. I bumped the brake coast timing tables up about 4 degrees in the low end and problem is solved completely. It coasts down like a stock car would! The tune is spot on now issues at all. Runs like the factory tuned it this way.