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Thread: Knock volts versus degrees of retard

  1. #1
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Knock volts versus degrees of retard

    Wondering if there is a list or graph that shows knock to retard degrees. In other words. how many knock volts equals one degree of retard?
    Thanks
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  2. #2
    Hybrid booster
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    Re: Knock volts versus degrees of retard

    I don't think it works that way but I'm curious as well.
    This is the way I interpret it: "if it's above this voltage, retard by this much"

    Have you verified that it actually retards or that the knock threshold is working? The SMEC tunes I've used seem to not change the knock threshold regardless of what I set it to. I've even set it to 5v across the board and it still showed knock AND MPSCAN showed the knock voltage was 1.2 AND it was pulling timing.

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    Supporting Member II Turbo Mopar Contributor tryingbe's Avatar
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    Re: Knock volts versus degrees of retard

    What you seek does not exist.

    http://www.thedodgegarage.com/turbo_sae_22.html

    Detonation sensor-

    A narrow band piezoelectric accelerometer is mounted in the intake manifold which is tuned to detect noise in the 6.15 kHz range. The computer compares the sensors output with the known frequencies that the engine is know to vibrate at. If the computer determines what it is detecting isn't normal background noise it starts retarding the timing in 4.2 degree increments (up to a maximum of 14.7 degrees) till the knocking ceases. This allows the 2.2 engine to operate on lower octane gasoline without engine damage.

    http://www.thedodgegarage.com/5digits_electronics.html

    On knock control...

    ...only getting 11psi boost... Now I read on the slip of paper that came with the computer and it said make sure the timing is set at what the manual says( I think 14 degrees) well I bumped mine up ( 16 degrees I believe) I know it was 2 degrees more that it was supposed to. Could this be my problem?

    YES.
    The stock setting is 12 degrees.
    The module monitors knock and will reduce boost if the knock persists. Remember that the knock system, on these vehicles, was primitive. Increased boost (even without spark knock), worn followers, higher lift cam, or an injector body that physically touches the manifold can generate "noise" that can be misinterpreted as knock. The sensor accuracy was not good enough to be able to differentiate between these "noise makers".

    Why even bring this up?

    Add some boost...
    An increase in combustion chamber pressure (higher boost) can produce an increase in audible combustion chamber noise. Simply placing an oscilloscope on a knock sensor circuit or monitoring knock voltage with a scan tool, at two different boost levels, will indicate this.

    Add some timing...
    As the combustion chamber pressure increases, the desire for higher spark advance decreases. Not until a proper/higher octane fuel is utilized, will the engine benefit from higher spark advance.

    BTW: With 100+ octane, it is still possible to knock (detonate). Too much spark advance, via the distributor OR calibration, can result in broken pistons, failed head gaskets, etc..

    Consider the computer control...
    The boost, spark, and knock are all manipulated (or monitored) by the computer. In this case, 1987 electronics are in use. If knock is detected,
    AND timing is retarded (by the module)
    AND the timing reduction amount reaches a specific level
    AND knock still persists..
    THE BOOST WILL BE DE-RATED.
    In this case, to a level that is currently being observed. All this CAN occur, without ever hearing audible knock.

    Possible fix:
    Place the timing at 12 degrees and try another test run.
    ** Consider resetting the module, at this time. This will reset the learned/stored values, that may have been obtained while the engine was detonating, IF knock was occurring.

    Additional thought:
    The module pins, in the red and blue connectors, can back out. And the module pins can also corrode and fail, due to condensation build-up. The plastic bag that is supposed to cover the module can fall short, when trying to keep water/moisture out. Many abnormal symptoms can occur, if there is a poor circuit connection. Make sure this is not the issue, by close inspection of the connectors, terminal pins/sockets, and where the wire is crimped to the terminal.
    Tailgate at your own risk.

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    Supporting Member II Turbo Mopar Contributor jonnymopar's Avatar
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    Re: Knock volts versus degrees of retard

    Quote Originally Posted by tryingbe View Post
    What you seek does not exist.

    http://www.thedodgegarage.com/turbo_sae_22.html

    Quote Originally Posted by www.thedodgegarage.com
    ...tuned to detect noise in the 6.15 kHz range
    Well, that's an interesting tidbit. Currently I'm using my original knock sensor in my 2.4L. I wonder if that frequency is even correct for the 2.4L!

    How the hell have I spent so many hours of my life reading over Gary's page and I still miss things?!

    /offtopic
    Jon J.

    1989 Daytona ES 2.4L DOHC
    2003 Neon SXT - gone but never forgotten

    Can't polish a turd? Sure you can! Just don't reuse the rag afterwards, dummy!

  5. #5
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: Knock volts versus degrees of retard

    Thanks all, I have an LM and a 2.5 in my Charger. I've noticed more than 1.5 kvlts with nothing displayed on my retard gauge. I did read The dodge garage article but need to look it over again...
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

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    Boost, it's what's for dinner... Turbo Mopar Staff Aries_Turbo's Avatar
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    Re: Knock volts versus degrees of retard

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    this is what defines whether there is knock retard.

    as you can see, even if you see 1.5v on the knock voltage readout, it can be below the threshold of knock as long as its above ~4000rpms.

    how much the ecu retards depends on how long the knock voltage stays above the knock threshold.

    Brian

    Quote Originally Posted by turbovanman
    This one is easy, I have myself to blame, I rush things, don't pay attention to gauges when I should, change to much stuff at once then expect miracles, the list is endless.

  7. #7
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: Knock volts versus degrees of retard

    Brian, It looks like knock voltage needs to hit the 5 volt level, is 5 volts is the knock threshold?
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  8. #8
    Boost, it's what's for dinner... Turbo Mopar Staff Aries_Turbo's Avatar
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    Re: Knock volts versus degrees of retard

    Look more closely. And go to mptune and look at this table. It is rpm dependent. Think of the knock sensor as a microphone. As the rpms rise, the overall noise of the block goes up. You can't have the system listening for noise of the same loudness at 2000 rpms and 5000rpm.

    It takes more knock sensor voltage to trigger knock events at higher rpm.

    Quote Originally Posted by turbovanman
    This one is easy, I have myself to blame, I rush things, don't pay attention to gauges when I should, change to much stuff at once then expect miracles, the list is endless.

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