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Thread: C7Z Knock/timing question

  1. #1
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    C7Z Knock/timing question

    Hey guys. I have a 2017 C7Z06 w/A8 trans i am tuning and have run into a weird problem and i have been banging my head against the wall for a couple of days on the dyno. The car is pretty much stock other than the following mods;

    *93 pump gas
    *2.3" upper pulley
    *Rotofab Big gulp intake
    *secondary cat delete

    The problem im having is im running into large ammounts of KR after 4500rpm when the car is tested in 5th gear. almost zero KR in 4th gear. I have tried the following things;

    *.79-.84 lambda, no difference other than overall power output
    *lowered or increased timing in small increments, no difference
    *reduced iat by running intercooler pump with fan on prior to test (80f to 120f IAT2 makes no difference)

    My plex monitor does show some audible knock at that point, so the KR seems valid. posted the last file and the two logs. Any ideas?

    shopz06_2400-6500_5th gear.hplshopz06_2400-6500_4th gear.hpl
    shopz06rev3.hpt

  2. #2
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    Not on tuning laptop at the moment to see logs, but do your torque values line up in the appropriate order in 5th gear? (peak>max>engine, driver axle>predicted and immediate axle, etc.)

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    Quote Originally Posted by RobZL1 View Post
    Not on tuning laptop at the moment to see logs, but do your torque values line up in the appropriate order in 5th gear? (peak>max>engine, driver axle>predicted and immediate axle, etc.)
    I have all the values maxed out in the rpm vs gear for Maximum torque.

  4. #4
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    Quote Originally Posted by jmstekguy View Post
    Hey guys. I have a 2017 C7Z06 w/A8 trans i am tuning and have run into a weird problem and i have been banging my head against the wall for a couple of days on the dyno. The car is pretty much stock other than the following mods;

    *93 pump gas
    *2.3" upper pulley
    *Rotofab Big gulp intake
    *secondary cat delete

    The problem im having is im running into large ammounts of KR after 4500rpm when the car is tested in 5th gear. almost zero KR in 4th gear. I have tried the following things;

    *.79-.84 lambda, no difference other than overall power output
    *lowered or increased timing in small increments, no difference
    *reduced iat by running intercooler pump with fan on prior to test (80f to 120f IAT2 makes no difference)

    My plex monitor does show some audible knock at that point, so the KR seems valid. posted the last file and the two logs. Any ideas?

    shopz06_2400-6500_5th gear.hplshopz06_2400-6500_4th gear.hpl
    shopz06rev3.hpt
    this seems to be an AFR problem, if you notice in 4th gear it commands more gas than in 5th gear, in 5th it seems that it is drying out and needs more fuel, try commanding more fuel, in case that does not work lower 6degrees to the whole table and see if there is still knock, if you can't contact me to see if we solve it more deeply, In my experience with these engines it's more like all the timing they don't like very much because it starts to knock
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  5. #5
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    Quote Originally Posted by Josue Galban View Post
    this seems to be an AFR problem, if you notice in 4th gear it commands more gas than in 5th gear, in 5th it seems that it is drying out and needs more fuel, try commanding more fuel, in case that does not work lower 6degrees to the whole table and see if there is still knock, if you can't contact me to see if we solve it more deeply, In my experience with these engines it's more like all the timing they don't like very much because it starts to knock
    Thanks for the reply. I have enrichened and lowered timing as per my first post. I am noticing the torque numbers and predicted are off and am look to see if thats the issue.

  6. #6
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    Back up your SOI about 5-8 degrees. Target .82 Lambda. On 93 pump, 2.3 pulley and without headers, you're not going to get anymore than about 17-18 degrees in it without knock. If you have access to flex fuel, put a sensor in it and run E20-E30 and you will get 20-21 degrees without knock.
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    Quote Originally Posted by TriPinTaZ View Post
    Back up your SOI about 5-8 degrees. Target .82 Lambda. On 93 pump, 2.3 pulley and without headers, you're not going to get anymore than about 17-18 degrees in it without knock. If you have access to flex fuel, put a sensor in it and run E20-E30 and you will get 20-21 degrees without knock.
    Thanks for the reply. Yes in 4th gear it was ok with 17-18 degrees as seen in the 4th gear sample log. 5th gear it would drop the timing like a rock when it sees KR. Im going to see if the new changes i made to the Torque management makes any difference and will take your SOI suggestion as well. The 5th gear pull is also almost 12 seconds long and made me think it was increasing in heat/heatsoak causing the knock, hence why i tryed the 4th gear pull and sure enough, no Knock. Just never ran into a problem like this before.

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    Quote Originally Posted by jmstekguy View Post
    Thanks for the reply. Yes in 4th gear it was ok with 17-18 degrees as seen in the 4th gear sample log. 5th gear it would drop the timing like a rock when it sees KR. Im going to see if the new changes i made to the Torque management makes any difference and will take your SOI suggestion as well. The 5th gear pull is also almost 12 seconds long and made me think it was increasing in heat/heatsoak causing the knock, hence why i tryed the 4th gear pull and sure enough, no Knock. Just never ran into a problem like this before.
    Higher gears will tolerate less timing due to load and heat. You can probably only get about 15-16 degrees in it in 5th gear and then let the knock sensors pull timing when needed. The LT4 in stock configuration on the stock tune has KR and will pull timing. Adding boost and not adding headers will only make it worse.
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    Quote Originally Posted by TriPinTaZ View Post
    Higher gears will tolerate less timing due to load and heat. You can probably only get about 15-16 degrees in it in 5th gear and then let the knock sensors pull timing when needed. The LT4 in stock configuration on the stock tune has KR and will pull timing. Adding boost and not adding headers will only make it worse.
    This is accurate. I have seen some LT4s have up to 8 degrees of knock, completely stock on 91 octane here in Arizona. This is by design. Lots of manufacturers seem to be leaning on knock sensors a lot more in factory calibrations these days.
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  10. #10
    try mixing in some higher octane fuel and see if it goes away.

  11. #11
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    Quote Originally Posted by TriPinTaZ View Post
    Higher gears will tolerate less timing due to load and heat. You can probably only get about 15-16 degrees in it in 5th gear and then let the knock sensors pull timing when needed. The LT4 in stock configuration on the stock tune has KR and will pull timing. Adding boost and not adding headers will only make it worse.
    What you say is totally true, 5th gear is only generating more load and would need to lower timing, although I could also try it on the street maybe the IAT temperatures will help more and it will not have KR
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    Quote Originally Posted by TriPinTaZ View Post
    Higher gears will tolerate less timing due to load and heat. You can probably only get about 15-16 degrees in it in 5th gear and then let the knock sensors pull timing when needed. The LT4 in stock configuration on the stock tune has KR and will pull timing. Adding boost and not adding headers will only make it worse.
    Makes sense. The ambient temps are brutal this week here in BC Canada for a change from the normal rain. I wanted to confirm that timing and afr were safe prior to letting the car leave so there isnt any issues, i wasnt aware that they LT4's were pulling timing on stock applications. good to know. I appreciate your help.

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    Quote Originally Posted by Josue Galban View Post
    What you say is totally true, 5th gear is only generating more load and would need to lower timing, although I could also try it on the street maybe the IAT temperatures will help more and it will not have KR
    I agree, the temps in the shop are insane right now due to a heat wave here. I would love to take the car out at night and test in colder intake temps, but i also dont want to do 155mph in 5th to confirm it lol.

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    Quote Originally Posted by jmstekguy View Post
    I agree, the temps in the shop are insane right now due to a heat wave here. I would love to take the car out at night and test in colder intake temps, but i also dont want to do 155mph in 5th to confirm it lol.
    If you're loading up the dyno, it would be more prone to knock on the dyno vs on the street where it is getting a lot of fresh air flow. Your timing and fuel are not out of range. I would still back the SOI up so that it peaks around 360-365 up top and see if you see an improvement.
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    Quote Originally Posted by jmstekguy View Post
    Makes sense. The ambient temps are brutal this week here in BC Canada for a change from the normal rain. I wanted to confirm that timing and afr were safe prior to letting the car leave so there isnt any issues, i wasnt aware that they LT4's were pulling timing on stock applications. good to know. I appreciate your help.
    Almost any and every GEN4 and GEN5 performance vehicle pulls timing due to some knock, when they are completely bone stock. That's the way the system is designed to work. A high octane table with maximum tolerable timing, knock sensors to detect knock, multiple knock retard tables and a low octane table to switch to when the KR is consistent enough.

    If you happen to come upon a performance vehicle with absolutely NO knock, suspect it's been tampered with. Either knock sensors deadened to the point of not working, or it's been neutered.

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    Quote Originally Posted by TriPinTaZ View Post
    If you're loading up the dyno, it would be more prone to knock on the dyno vs on the street where it is getting a lot of fresh air flow. Your timing and fuel are not out of range. I would still back the SOI up so that it peaks around 360-365 up top and see if you see an improvement.
    Yes its a Mustang dyno. Confirm last run on the dyno tolerated 18-19 deg timing at .82 lambse in 4th gear, 5th gear was showing 2-3 degrees of KR. Ill log it at the track to confirm 5th gear fueling at max timing on good fuel. SOI was 366 on last log up top. Thanks again for the help.

  17. #17
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    Just leave the knock sensors stock and let it pull timing via KR in 5th gear. If anything you can increase the recovery values to like .250 in the higher RPMs so that it recovers faster. Technically, if you have the IAT timing pull slope correct, the car will start pulling 2 degrees of IAT timing by 5th gear.
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