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knocking noise?

This is a discussion on knocking noise? within the Internal Engine forums, part of the LSx Technical Help Section category; I just bought an 01SS. car drives great, but I've noticed when I turn my car off after a ride ...

  1. #1
    Impounded wicked illusions's Avatar
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    knocking noise?

    I just bought an 01SS. car drives great, but I've noticed when I turn my car off after a ride I here a small knocking noise coming from under the car. I dont know if its from the engine or maybe the heat of the exaust(flowmaster) that is causing this. I've hered this same sound on other makes of cars but It kinda trips me out. It almost soung like a small knock on a pan and it does it about every minute after car being shut off and last about for 5 min.then goes away. It also does it when car is cold and I start it up. I am also pumping 87 unleaded fuel can this be a reason??? Is all this normal?Iam I just fraking out? someone help please..

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    Member z28misfit's Avatar
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    it may just be the exhaust contracting back after it starts to cool down. it might just be mostly the cats making the noise. that would be my best guess. maybe i'm dead wrong.

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    Member DocEwww's Avatar
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    Why are u using 87 octane in a LS1? What type of oil are u running?

    2001s are notorious for the piston slap. That'd explain a knocking from underneath on startup.

    Not sure what this noise is that you talk about after the car is shut off.

  4. #4
    Impounded wicked illusions's Avatar
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    mobil 1 senthetic. yeah I think ot might be the exaust.....

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    Senior Member Street Lethal's Avatar
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    Quote Originally Posted by z28misfit
    ...it may just be the exhaust contracting back after it starts to cool down.
    Agreed.

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    Veteran Hi-Po's Avatar
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    Quote:
    Knocking (also called pinking or pinging)—technically detonation—in internal combustion engines occurs when fuel/air mixture in the cylinder has been ignited by the spark plug and the smooth burning is interrupted by the unburned mixture in the combustion chamber exploding before the flame front can reach it. Combusting stops suddenly, because of the explosion, before the optimum moment of the four-stroke cycle. The resulting shockwave reverberates in the combustion chamber and pressures increase catastrophically, creating a characteristic metallic "pinging" sound.

    Detonation

    The fuel/air mixture is normally ignited slightly before the point of maximum compression to allow a small time for the flame-front of the burning fuel to expand throughout the mixture so that maximum pressure occurs at the optimum point. The flame-front moves at roughly 33.5 m/second (110 feet/second) during normal combustion. It is only when the remaining unburned mixture is heated and pressurized by the advancing flame front for a certain length of time that the detonation occurs. It is caused by an instantaneous ignition of the remaining fuel/air mixture in the form of an explosion. The cylinder pressure rises dramatically beyond design limits. If allowed to persist detonation will damage or destroy engine parts.

    Detonation can be prevented by:

    * The use of a fuel with higher octane rating
    * The addition of octane-increasing "lead," isooctane, or other fuel additives.
    * Reduction of cylinder pressure by increasing the engine revolutions (lower gear), decreasing the manifold pressure (throttle opening) or reducing the load on the engine, or any combination.
    * Reduction of charge (in-cylinder) temperatures (such as through cooling, water injection or compression ratio reduction).
    * Retardation of spark plug ignition.
    * Improved combustion chamber design that concentrates mixture near the spark plug and generates high turbulence to promote fast even burning.
    * Use of a spark plug of colder heat range in cases where the spark plug insulator has become a source of pre-ignition leading to detonation.

    Correct ignition timing is essential for optimum engine performance and fuel efficiency. Modern automotive and small-boat engines have sensors that can detect knock and retard (delay) the ignition (spark plug firing) to prevent it, allowing engines to safely use petrol of below-design octane rating, with the consequence of reduced power and efficiency.

  7. #7
    maroonZ
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    Use Sunoco ultra 94 or some decent 93 octane gas and see if that helps

  8. #8
    Impounded wicked illusions's Avatar
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    I drove all around town trying to get rid of the shitty gas. I pumped at a chevron station. The higher ratting they offered was 91. once I pumped that I really noticed a difference on acceleration. w/ the old gas when I hit my 3rd gear and stomped on the gas a hered a small rattle once in a while. w/ the new gas I havent really noticed it so far. I really think that knocking/tapping noice was my exaust cooling. but I nottice that same single taping(barely any) when I first turn on the car. can that be the exaust getting hot?

  9. #9
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    i would never use anything less than 92 octane

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