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  1. #1
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    Long Tube Headers and False Knock

    Have any of you that installed long tube headers discovered that the your car picked up a false knock signal which retards timing, and thus restricts power?

    I'd like to install long tubes and run a before and after dyno to monitor the amount of torque and horsepower that they increased. I had just did that with a LMI 392 True CAI.

    After the upgrade of intake and headers without a tune, then I wanted to see how much a tune would help.
    Terry

    2005 Magnum RT load runner 2.6: Inertia Motorsports 419 Stroker, Predator Tune: 475rwhp & 465rwtq, Crower Cam, Kook's Headers, 3 inch "Custom" Exhaust, Tunable Induction Intake, NAG1-HTC Tranny, 3.55 Gears, 600hp DSS Half-Shafts, TrueFiber Challenger Hood, Enkei Wheels 18"x9", MT 28.00" / 12.00" x 18" radials on rear, Paneled Rear Side Windows, GoManGo Front Seats, Eibach Springs/Dampers, Wilwood Calipers, Rear Wiper Removed, Billet Technology enhancments.
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  2. #2
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    Yes I have false knock with Lt headers on a 6.1. And yes I did a before and after with the lmi but not on the Dyno at the track and picked up 3/10. My time slips are in his Facebook page
    The lmi true cold air is no joke. It works


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  3. #3
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    Turn off the knock sensors and runs the test passes.

  4. #4
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    I left the sensors turned on. AJ said there’s no harm in it. It’s a street car so I don’t care


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  5. #5
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    Quote Originally Posted by Renfrick1 View Post
    Yes I have false knock with Lt headers on a 6.1. And yes I did a before and after with the lmi but not on the Dyno at the track and picked up 3/10. My time slips are in his Facebook page

    sent from my iPhone using Tapatalk
    Quote Originally Posted by DBL.DWN View Post
    Turn off the knock sensors and runs the test passes.
    Quote Originally Posted by Renfrick1 View Post
    I left the sensors turned on. AJ said there’s no harm in it. It’s a street car so I don’t care


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    Let me try to get some clarity on the above posts:
    1. Is it safe to say that both of you have a tune? Isn't that how it is possible to turn the knock sensors on/off?
    2. If the knock sensors detect the knock, whether it is an actual knock or a false knock, doesn't the computer pull the timing, and thus lose power?

  6. #6
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    The knock sensors can have their sensitivity altered without turning them completely off. CMR tune required.
    Old 426 guy,
    Jim

  7. #7
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    Quote Originally Posted by RT NOMAD View Post
    Let me try to get some clarity on the above posts:
    1. Is it safe to say that both of you have a tune? Isn't that how it is possible to turn the knock sensors on/off?
    2. If the knock sensors detect the knock, whether it is an actual knock or a false knock, doesn't the computer pull the timing, and thus lose power?
    Yes the knock sensor will pull timing (and lose power) if it correctly or falsely picks up a knock.
    I dont see the need for them.

  8. #8
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    Yes I have a blower and tune. I left them on for safety. I’m not out to break records. I trust AJ ‘s tune but like I said. I’m out having fun. I don’t care if it pulls timing


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  9. #9
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    Quote Originally Posted by Renfrick1 View Post
    Yes I have a blower and tune. I left them on for safety. I’m not out to break records. I trust AJ ‘s tune but like I said. I’m out having fun. I don’t care if it pulls timing


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    That explains it!

    PB ET 14.02 at CamaroFest 5 totally stock
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  10. #10
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    Let’s race !!


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  11. #11
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    Also for clarity, the knock sensors are located low on each side of the block, well below the headers... While it's true that LT headers can emit a high pitch ping sound, this is mainly an echo that's resonating along the outside of the LT headers. If you think that there's a knock (real or false) run a data log and look for the presence of the knock and the conditions under which it's appearing. You can also use a mechanics stethoscope to isolate where the sound is coming from (obviously not while driving on the street). Also, while it's possible to desensitize the knock sensors in the tune, it's much safer to keep them active rather than turning them off. There are a number of other sensors that can be turned off to get more enjoyment out of your ride, talk to your tuner about which ones to turn off. Just know that, depending on where you live, you might need to reactivate all the sensors before going for a state emissions test.

  12. #12
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    How are you determining that it's false knock and not real?

  13. #13
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    Quote Originally Posted by jdm7 View Post
    How are you determining that it's false knock and not real?
    A real knock shows up in the data log... The knock sensor itself is very simple, if it gets shaken too much the internal circuit is closed and the knock is captured by the PCM/ECU. A false knock or echo, is audible but doesn't cause the knock sensor to trigger. Another thing that can cause a false knock to be registered is associated with the engine mounts which are located near where the knock sensors are installed. A broken or severely cracked engine mount may cause the knock sensor to trigger. Remember, a knock is typically caused by piston shutter against one or more cylinder walls.

  14. #14
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    Please tread carefully when dealing with your knock sensors. Yes, modifications to the engine and mounts can alter the resonance in the block that the accelerometers detect, but if you just have a tune or exhaust mod then the sensors are still working correctly. If you hear a knock or ping, but don't see any spark pull out, try putting in higher octane - if the noise goes away it was probably knock, if it stays then likely some other noise. If you see spark getting pulled out and don't believe it is correct, again try putting in high octane race fuel - if the pull out goes away then it's real knock, if you still have knock on race fuel then it's false knock (or a really, really bad tune).

    Knock sensors are accelerometers, they are tuned to detect a specific high frequency resonance that knock induces, in a specific crank-angle-window for each cylinder. There is one sensor for each bank of a HEMI engine, but if any one cylinder has knock, spark is pulled out of all cylinders. Chrysler's control system does not allow the knock sensor to put in more spark than what's in the base tables (it can take away, not add, which is why running higher than recommended octane fuel doesn't improve performance. Some OEMs allow the knock system to add spark until it detects knock.)



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