What is spark plug knock?

[hoodup]

what is this and how do you correct it? I think i have it since i replaced my plugs.

What causes it to happen?

[wildwilly4x4]

....Spark knock?? Spark knock is a condition of using low grade fuel, too high of compression engine for a lower grade fuel, using higher heat range plugs and too low of a grade of fuel, or too far advanced ignition timing for a low grade fuel. Spark knock almost always goes back to the grade of fuel you are using, although it can happen if your timing is too far advanced. It goes back to the octane rating on fuel (its ability to NOT ignite). If all you did was replace the plugs in oyur motor, you may have gotten a "hotter" spark plug (hotter plugs dont mean the spark hotter, it means that they hold in more heat from the combustion process).

Spark knock is basically defined as the fuel igniting before it is supposed to. Using a low grade fuel (say 87 octane) will ignite more easily than say 91 octane. If you used a "hotter" spark plug your fuel may possibly be "lighting off" before the spark plug actually sparks, giving you spark knock. The actual knocking you hear is the combustion process actually fighting against the piston as it travels up on the compression stroke.

You can try a better grade of fuel, retard you timing a bit, or if that doesnt fix it, try running a "cooler" spark plug.

Spark knock is actually the reason race cars have to use "race fuel". Since race and high performance engines use higher compression ratios, along with more advanced timing, they have to run a higher octane fuel, which keeps the fuel from igniting just from the heat of compression.

Hope this was able to help you a lil bit, maybe someone else can chime in with some other tips. Good luck!

[badriv455]

Wild Willy pretty much hit the nail on the head. I just wanted to add that this condition is also commonly refered to as "pinging"

[Leviticus]

Originally Posted by hoodup

what is this and how do you correct it? I think i have it since i replaced my plugs.

What causes it to happen?

One thing to be sure of is that you gapped them properly. If you are running an HEI you will want a wider gap at .045 IIRC. If the gap is too small, it can cause this condition.

And great info WildWilly!