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Thread: Excessive knock retard on L67

  1. #1
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    Excessive knock retard on L67

    Hi guys, I am scratching my head at why my L67 car is knocking so damn much and I'm having to pull so much timing. Its not a stock car, and I'll briefly list the mods I've done just for reference.

    • CAI
    • 180 TStat
    • Autolite Copper 103 plugs
    • 3.4" SC Pulley
    • ZZP Headers and 3" downpipe
    • Custom 2.5" exhaust
    • 1.9:1 Rockers
    • Northstar throttle body
    • Ported supercharger blower housing


    Talking with some guys on 3800 forums, most people run high teens in their WOT timing for cars with similar mods, yet I am barely able to get above 10 degrees, not to mention a couple cells requiring as low as 2-3 degrees to be knock free. Some things I have done and crossed out are

    • Replaced louvered core resonator with a Vibrant perforated core one
    • Compression test (Passed fine)
    • Cut out and installed a new high flow cat
    • Ran 1 and a half tanks of injector cleaner
    • Dropped another step colder plugs from Copper 104s to 103s


    After doing all that I maybe gained 2 degrees of timing max, I am still around 10-11 degrees WOT. Using TrackAddict, I am barely below 15s in the quarter, which the car has run bone stock years ago, so something is clearly up and it is not making nearly the power it should be (IIRC with these mods it should roughly be high 13s low 14s).

    What else can I check/try here? Am I doing something horribly wrong with my tune that's causing it? Or is this most likely something with the engine? Its got 170k miles on it, could I have an injector getting bad and leaning out one cylinder? I attached my most recent scan and tune, I'll also put a screenshot of my table before I did some smoothing to see just how much I had to subtract out of it from the scan.

    Capture.PNG

    Copper drive 3.hpl
    Copper drive 3.hpt

  2. #2
    Advanced Tuner ZeroBoostBuick's Avatar
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    What gasoline grade ?

    Did you tune the MAF Open Loop WOT with a wideband ?

    Did you verify and/or adjust the spark gap before installing the plugs ?

    Obviously, in the heat of the summer you're gonna have more KR than otherwise.

    The spark timing doesn't seem too low, considering the intake tamps.

    Those running higher timing are probably running E47 or E85

    In case you ever get shitty gas, I would lower the whole Low Octane table by at least 3 degrees.

    Set the base Power enrichment in all boxes above 120 f to 11.6 or whatever you want and zero out the "add vs rpm" table.

    Your tune needs a bit of cleaning up. No big deal as long as your lower octane table is lowered enough to save the motor when shit hits the fan.

    Also, in the trans, torque converter, apply/release. Change the 4th apply to 52 - 52 - 60 for the fist three boxes. You have them set to 48 - 48 - 52 which doesn't make sense because you're shifting into 4th at 50 - 50 - 55 mph and you're trying to command overdrive in 4th at lower speed than the 4th gear shift. Sometimes some cars can have a shutter during that 3-4 shift at those throttle positions because of that factory mistake.

  3. #3
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    Quote Originally Posted by ZeroBoostBuick View Post
    What gasoline grade ?
    Shoulda mentioned that, 91.

    Quote Originally Posted by ZeroBoostBuick View Post
    Did you tune the MAF Open Loop WOT with a wideband ?
    Yeah I have a wideband and tuned the MAF in open loop

    Quote Originally Posted by ZeroBoostBuick View Post
    Did you verify and/or adjust the spark gap before installing the plugs ?
    Yep, set them to 0.045"

    Quote Originally Posted by ZeroBoostBuick View Post
    Obviously, in the heat of the summer you're gonna have more KR than otherwise.

    The spark timing doesn't seem too low, considering the intake tamps.

    Those running higher timing are probably running E47 or E85
    I do plan on running E85 eventually. Its still sluggish feeling though, and if we are trusting track addicts numbers running slower than stock even.

    Quote Originally Posted by ZeroBoostBuick View Post
    In case you ever get shitty gas, I would lower the whole Low Octane table by at least 3 degrees.
    Yeah I drop the low octane table by 3-4 when I'm flashing a tune I will be running for a while on.

    Quote Originally Posted by ZeroBoostBuick View Post
    Set the base Power enrichment in all boxes above 120 f to 11.6 or whatever you want and zero out the "add vs rpm" table.
    Whats the reasoning behind doing this? My reasoning behind what I have for the Add vs. RPM table was that it would enrich as I stay in PE longer, which from what I understand would be a good idea with the supercharger heatsoak.

    Quote Originally Posted by ZeroBoostBuick View Post
    Your tune needs a bit of cleaning up. No big deal as long as your lower octane table is lowered enough to save the motor when shit hits the fan.
    Cleaning up as in the spark tables? Yeah I'm aware of that, I'm still in the middle of sorting out the spark advance. I added some 110 race fuel in and the knock disappeared, so at least I know its actual knock and I'm not getting false knock.

    Quote Originally Posted by ZeroBoostBuick View Post
    Also, in the trans, torque converter, apply/release. Change the 4th apply to 52 - 52 - 60 for the fist three boxes. You have them set to 48 - 48 - 52 which doesn't make sense because you're shifting into 4th at 50 - 50 - 55 mph and you're trying to command overdrive in 4th at lower speed than the 4th gear shift. Sometimes some cars can have a shutter during that 3-4 shift at those throttle positions because of that factory mistake.
    Ah gotcha, yeah I'll change that.

  4. #4
    Advanced Tuner ZeroBoostBuick's Avatar
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    Try to use 93-94 octane in the summer if it's available in your area.

    I took another quick look at the scan and I see you're running a wideband. The WOT AFR looks good.

    WOT MAF could use a little sharpening. Nothing that needs immediate attention. I'm referring to the AFR command and wideband readings not matching, but they're close enough.

    You're VE table looks like it needs some help. I'd put it back to stock and let it be.

    What I keep going back to, is you say the car feels slow as if there is something pulling it back. There is nothing in the tune that stands out as a possible cause. I'm wondering if there is something mechanical going on.

    Engine / Torque Management / Spark Retard - vs torque reduction... set the whole table anywhere from 0 to 15... I've always set that table to 0.

  5. #5
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    Quote Originally Posted by ZeroBoostBuick View Post
    Try to use 93-94 octane in the summer if it's available in your area.

    I took another quick look at the scan and I see you're running a wideband. The WOT AFR looks good.

    WOT MAF could use a little sharpening. Nothing that needs immediate attention. I'm referring to the AFR command and wideband readings not matching, but they're close enough.

    You're VE table looks like it needs some help. I'd put it back to stock and let it be.

    What I keep going back to, is you say the car feels slow as if there is something pulling it back. There is nothing in the tune that stands out as a possible cause. I'm wondering if there is something mechanical going on.

    Engine / Torque Management / Spark Retard - vs torque reduction... set the whole table anywhere from 0 to 15... I've always set that table to 0.
    Alright I'll take a look at that stuff in the tune. Yeah I'm not really sure whats going on, I think I'm gonna take it to a dyno and just see what numbers it is making. I dynoed it last summer so I can compare and see how it's doing, and if they have any ideas about why it would feel sluggish.