Most people describe the combustion stroke as a bang or explosion, but this is not accurate. During the combustion stroke, there should not be an explosion, but rather a controlled burn. Under proper operating conditions, the spark plug should create a flame-front with the air/fuel mixture which causes the gasses to expand and push the piston back down the cylinder. When Knock, detonation, or pre-ignition occurs, the air/fuel mixture is ignited at an improper time in the cycle. Many times these terms are used interchangeably though they are technically different.
Detonation is an uncontrolled combustion event which occurs after the spark event.
Pre-ignition is an uncontrolled combustion event which occurs before the spark event.
Knock (pinging) is the actual noise that can be audibly heard if detonation is bad enough. Most OEM knock sensors are basically microphones tuned to listen for a specific frequency to detect this noise. When some is describing knock, they are generally referring to detonation.
Severe detonation over an extended time can damage pistons, rods, rod bearings, and other engine parts. If you can audibly hear knock, then it’s time to verify your tune and fuel.
Which brings us to our next point, octane. A fuel’s octane rating is a measure of a fuel's ability to resist detonation. The higher the octane rating, the more resistance it has to detonation. Many of the vehicles that are supported by Dynojet products have a knock sensor. While a knock sensor is a great tool to correct for bad ignition events, they are reactionary… meaning they do not change anything until an event has occurred. Other vehicles Dynojet supports do not have a sensor at all meaning proper fuel and a proper tune for the installed parts is even more critical.