Knock retard .. I am trying to learn ...is this accurate ?

[grass doctor]

KR is a result of detonation. To have ‘real’ (more on ‘real’ vs ‘false’ KR later) KR, you MUST have detonation. Detonation is the uncontrolled combustion of the intake charge. “Uncontrolled” means that the mixture ignites via a means other than the spark from the spark plug. In most cases, the uncontrolled ignition is due to a ‘hot spot’ in the cylinder. Hot spots can be caused by uneven combustion, spark plugs that are rated too ‘hot’, lean fuel conditions, breathing restrictions (exhaust / intake), bad gas, and so on. One problem in particular is the head gaskets. During an engine teardown, the head gaskets are NOT made perfectly round. Some of the gasket material actually protrudes slightly into the combustion chamber. Since the head gasket bore linings are made of metal the bit that protrudes into the cylinder will glow red hot, thus creating the potential for a nasty ‘hot spot’. This is an example of an area that should be checked and perhaps replaced with an aftermarket head gasket. In other cases, the ‘hot spot’ is due to unreasonably high cylinder compression. Either way, the ‘pinging’ or ‘rattling’ sound you hear is the result of the actual collision of the flame front produced by the ‘hot spot’ and the normal flame front produced by the spark plug. Typically, these two flame fronts are opposing fronts, meaning that they are expanding, or propagating toward each other, causing the collision. Real KR does NOT occur without detonation occurring FIRST.

 

[1986 Buick GX1]

I believe engine timing is based on the rate of combustion as well.
If the fuel/ air mix is ignited by the spark plug and explodes instead of burns, the force is exerted on the piston before top dead center instead of after top dead center causing the knock sound and the damage.
Cylinder temp, fuel quality and fuel/ air mix all contribute to the proper burn rate.
Any of those not being correct can cause pre-ignition (detonation) and knock.

This was the main reason for running a 160 deg. thermostat in the early days of performance chips. It was believed that higher timing was the key to more power.

Lower cylinder temps were needed to allow the higher timing to start the power stroke after top dead center, not before.

I’m sure there is more involved, but that’s all I know.

 

[TexasT]

The knock sensor is "listening" for a certain sound. Unfortunately this sound can be similar to a down pipe banging on the frame, other metal parts hitting together and something that jars the block to make it move similar to the knock signature.

 

[turbo nasty]

I believe engine timing is based on the rate of combustion as well.
If the fuel/ air mix is ignited by the spark plug and explodes instead of burns, the force is exerted on the piston before top dead center instead of after top dead center causing the knock sound and the damage.
Cylinder temp, fuel quality and fuel/ air mix all contribute to the proper burn rate.
Any of those not being correct can cause pre-ignition (detonation) and knock.

This was the main reason for running a 160 deg. thermostat in the early days of performance chips. It was believed that higher timing was the key to more power.

Lower cylinder temps were needed to allow the higher timing to start the power stroke after top dead center, not before.

I’m sure there is more involved, but that’s all I know.

Higher/more/advancing timing is earlier in compression to power stroke. Lower timing..later

Reducing/Lowering/retarding timing. It reduces potential to capture peak cylinder psi by firing ignition later in piston travel. Too late and potential is wasted and mixture burns late and towards/into the exh stroke.

Raising/Higher/Advancing timing. It increases the potential to capture peak cylinder psi firing earlier in piston travel. Too early and the mixture fires while piston is still traveling up and said cylinder fights the rising piston promotes knock.

Timing means just that......timing the spark to ignite the mixture at the proper time to capture the peak combustion psi in cylinder of mixture used to to make power on BANG stroke lol. Many other variables play into this but thats what it is.

 

[grass doctor]

The knock sensor is "listening" for a certain sound. Unfortunately this sound can be similar to a down pipe banging on the frame, other metal parts hitting together and something that jars the block to make it move similar to the knock signature.

yes rich ... and I just did some research on the differences between the the two ESC modules ... the 86 BLO vs the 87 HKP .. with Antony P who spoke with Richard Clark on the differences ...it all started with a weird part I got from bruce that had HKD on knock module , which traces back to 85 turbo riviera and t-type century hopefully he will chime in and give the conversation we had the other day .. thank you for your time and input Buick brudda

 

[TexasT]

We really do things on the edge by tuning with the spark knock. It is a tremendously damaging force. If you can stay out of it you will be in much better shape. These cars have been around the block and the timing and fuel requirements are pretty well known to keep one from detonating.

 

[grass doctor]

We really do things on the edge by tuning with the spark knock. It is a tremendously damaging force. If you can stay out of it you will be in much better shape. These cars have been around the block and the timing and fuel requirements are pretty well known to keep one from detonating.

agreed... not wanting to go to the edge ... just curious on the OP if this a correct definition and congruent for most normal operating engines ... thank you for your input as always ... like to hear all views on this subject

 

[RmvBfrFlght]

Detonation and pre-ignition are two different things. Detonation occurs after the spark plug fires. It is when someplace in the chamber as the pressure increases another flame starts. This flame front and the one started by the spark plug then produce a high pressure spike.

Pre-ignition occurs before the spark plug fires. And is usually caused by a hot spot in the chamber. Pre-ignition is much more damaging to an engine then detonation. As the heat and pressure increase as the piston is still on its upward travel. This can destroy the piston in short order.

As for the '86 BLO vs the '87 HKP knock filters, they have the same specifications as to gain, center frequency and so on. The difference between them is that the '86 BLO filter is a 4-pole unit (part of the electronics inside), while the '87 HKP is a 2-pole filter. As such the '86 BLO filter is typically more discriminating (less likely to report false knock).

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