Author Topic: Timing Ping/Spark Knock  (Read 1079 times)

Offline bigben5054

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Timing Ping/Spark Knock
« on: September 19, 2020, 05:43:16 PM »
I'm a little embarrassed to admit that as much as I have heard the term "ping" as it relates to having too much advance timing, I don't actually know what it sounds like.  I have also seen "ping" referred to as "spark knock."  To me, a "ping" and a "knock" are two different sounds.  I've searched YouTube for a good video that demonstrated the sound, but I don't think YouTube videos are very good at capturing the audio.  Can anyone describe it to something I might be able to relate to?  I am in the process of fine-tuning my carb and when I snap the throttle off idle I hear a knock (just once) that sounds like its coming from the flywheel/clutch area.  Just wondering if I could be hearing a timing ping.  I'm set at 12 degrees advance at idle.  350 sbc with vortec heads.  Thanks. 

Offline bd

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Re: Timing Ping/Spark Knock
« Reply #1 on: September 19, 2020, 07:22:38 PM »
"Ping" is the loud ticking sound produced by preignition and minor detonation. 
"Knock" is a very loud hammering sound produced by major detonation.  Knock can also result from metal collisions.

Preignition occurs when fuel and air ignite within a combustion chamber prior to the ignition spark creating a single flame front.  The expanding gases push down on the top of the piston prematurely before the piston reaches its optimum position within the cylinder.  Preignition is akin to tapping the top of the piston with a small hammer.  The "size of the hammer" depends on the timing of the preignition.  Typically, the "ping" created is reminiscent of a couple of BBs in an aluminum soda can that is violently shaken end-to-end.  However, depending on the timing of preignition, the "ping" can be more severe to the extent of small marbles rattling in a can.  Preignition often is caused by a hot spot within the combustion chamber such as overheated spark plug electrodes as well as excessive compression pressures.

Detonation occurs when a second pocket of fuel and air ignite within the combustion chamber after the ignition spark has occurred, resulting in two colliding flame fronts.  The collision of the two flame fronts effectively creates a supersonic acceleration at their intersection that results in a "ping" if minor, or "knock" if major.  The resulting extreme pressure created by detonation is akin to hitting the top of the piston, cylinder head, and cylinder walls with a BIG hammer.  Prolonged detonation can be very destructive to the entire combustion chamber, the rods, the crankshaft, and the block webbing.  The "knock" created is reminiscent of a small marble shaken in a plastic coffee can to a hammer striking the cylinder head, depending on severity of effect.  Detonation can be caused by one or more hot spots within a combustion chamber such as carbon peaks, sharp edges, and poor squish/quinch as well as by overadvanced ignition timing and poor coolant circulation through the cylinder head water jackets.

Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline bigben5054

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Re: Timing Ping/Spark Knock
« Reply #2 on: September 19, 2020, 08:21:48 PM »
Very helpful explanation.  Thanks Rich!