what does knock mean?

[johnmac240]

i read people watching and being aware of knock at high boost and i was wondering what that ment

 

[DSMDEMON93]

Usually a "knock" or pinging comes from pre-ignition (detention) of the fuel/spark. The knock sensor picks up on this and it automatically retards your ignition timing to prevent damage.

 

[agentorange313]

I believe this have been touched upon in the forums:

knock, or "engine pining" is what occurs when there is a incomplete combustion of a chamber. this can happen form self detonation of fuel, extreme operation temps, imbalanced fuel.air mixture

The term comes from the sounds you can hear your engine make when there is incomplete combustion. It sounds like a knocking or a pinging.

All turbo dsm have a knock sensor. This sensor tell the PCM when there is detonation occurring in the engine. the pcm will retard timing. Its a piezoelteric device. It works like a microphone and picks up noise/vibration. Its got a tiny crystal inside.

People watch for knock when tuning because it is a sign of engine detonation and possible engine failure if left uncorrected.

For DSM, a lot of us run into something called phantom knock. When data logging, we can see how many counts of knock our engine is creating and if we need to retard the timing. Sometime, and external or internal sound can set off the knock sensor. I know in my expeerience, my #@%$#@^$%^ old lifter used to tick so bad that it would set off the knock sensor.

hope this helped

goodluck


I am sure there is someone who can give a better explanation if mine is incomplete and/or incorrect.

 

[iwillnotbleed]

"Knock" happens when your air/fuel mixture detonate's (explode's) before your piston reaches top dead center. This is something that people watch out for because if your a/f mixture detonate's before top dead center your combustion is fighting against the way that you crankshaft is supposed to spin. In easier term's, the combustion is trying to push your piston's backwards.

There's my explanation of it. As you learn more about your car I'm sure you'll find a better explanation. Also, if you don't have a way to watch for "knock", I suggest leaving your car stock until you do have a way. Hope this helps.

 

[dasithkg]

pretty good explanations all around!

Knock is basically detonation!

Combustion is actualy a controlled fire inside the cylinder, but knock creates a wave inside it! (like when a bomb explodes) There is a thin coat of oil 0n the pistons and the cylinder walls to protect them from being damaged from high pressure and the controlled combustion!

When knock happens, that thin coat of oil gets destroyed and thus exposes the bare metal to that wave! First wave destroys the protection and waves after that will make holes 0n the walls and pistons! If left uncorrected! Am talking about a massive knock. A small amount of knock wont do that kinda damage! But overtime it will

 

[TunaTalon]

There is a good write up in section 3.1 of http://www.jcmmachine.com/PDF files/JCM Tech Report ch3.pdf

All this is good to know before pushing your 4G63 for more than double stock HP levels.

 

[burkgonzo]

Knock sucks, I am dealing with knock on my tune right now. Also when your car reads knock it pulls alot of power or timing out of it. Less power sucks as well.

 

[navyvr4]

knock can cause major damage to your engine since it can only handle so much pressure. when knock happens, extreme pressure transients from predetonation or random combustion can create these extreme pressure waves that reak havoc on your engine internals.