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Basic explanation for knock and detonation

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Yeo
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Basic explanation for knock and detonation

Postby Yeo » April 27th, 2005, 7:47 am

Detonation when the air/fuel mixture in the cylinder explodes, instead of burning rapidly.
(To be really technical, detonation is when the flame front moving through the cylinder exceeds
the speed of sound.)

This is bad for two main reasons:

1) The sudden shock load can break parts - the repeated shock loads of constant detonation is like running a jackhammer in your engine.
2) The temperature inside a detonating cylinder is much hotter than normal, and can get hot enough to melt aluminum.

Symptoms of detonation:

1) A loud pinging or rattle/knocking noise. It sounds like a bunch of marbles inside a tin can. (This is why detonation is commonly called "knock")
2) Higher than normal exhaust gas temperatures
3) Little "flyspecks" of aluminum on spark plug center electrodes and the center insulator. This is the dead giveaway indicator for detonation. Examine your plugs with a magnifying glass. Little balls of aluminum clinging to the plugs means that you are detonating.
(It's aluminum from the pistons being vaporized and condensing on the plugs)
4) Engine damage (holes in pistons, melted spark plug ground electrodes, etc.

Causes of detonation:

1) Low octane fuel
2) High static compression ratio
3) High boost levels
4) Excessive spark advance
5) Lean fuel mixture (may be insufficient fuel pump capacity/pressure, insufficient
injector flow, air flow sensor out of range)
6) High inlet air temperature / low air density

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Postby Pinky » May 7th, 2005, 11:20 am

Don't kmock it till you rock it :!:

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Postby Maserati » August 6th, 2005, 4:54 pm

thanks yeo..learned some thing there

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Postby achillies » October 12th, 2005, 6:36 am

good looking mayn

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Postby 13 GHOST » November 12th, 2005, 7:41 am

What is pre-detonation is it same as detonation

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Postby Silvermike » November 23rd, 2005, 4:56 pm

is it necessary that u hear the knockin sound?
what would be the symtoms in terms of the peformance of the engine?

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Postby X2 » March 2nd, 2006, 5:05 pm

Silvermike wrote:is it necessary that u hear the knockin sound?
what would be the symtoms in terms of the peformance of the engine?



Detonation often occurs without your knowing or hearing it. Small levels of detonation or sparse instances of it MIGHT NOT damage parts, but the more audible, the worse it is. If the knocking/pinging sound is actually heard from the cockpit area... it means it's hardcore.

As far as performance, at certain detonation levels, it may not affect performance much at all.... but when you get hit with hard pinging, you may notice a decrease in power output since all the power of combustion is no longer put to the piston, but rather all over the place, not necessarily straight down to the crank. If the engine has a knock sensor (detonation microphone), it may send the signal to the ecu, which would attempt to stop it by altering ignition timing and fuel delivery which will kill power.

1) A loud pinging or rattle/knocking noise. It sounds like a bunch of marbles inside a tin can. (This is why detonation is commonly called "knock")


I like to describe the sound more like a handfull of small steel ball bearings or shot gun beads shaken around in a coffee tin. I also find it sounds quite similar to a bad CV joint taking a corner.

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Postby Silvermike » March 2nd, 2006, 8:25 pm

^ so when the knock sensor sends the signal to the ecu the CEL will come on?

and ignition will be retarded... by how much?

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Postby Val » March 2nd, 2006, 8:59 pm

apparently not enough. My engine pinged quite audibly (I thought it was my CV joint actually) on Super Gas at WOT. Not so much at normal engine speeds. Then again, ignition isn't retarded at WOT. Premium gas does the job right for me.

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Postby X2 » March 3rd, 2006, 1:39 am

Honda ecu's do NOT read KS input at WOT, only partial throttle.

IF it pings at WOT, nothing will happen to ur timing.... the KS is only really meant to save the engine from bad gas... the kinda bad that pings on light throttle and low advance.

Silvermike, when the ecu sees input from the KS, there is no CEL displayed, the ecu will simply recalibrate the timing and fueling lookups to suit... you cannot tell it has been done except for the drop in torque and increased gas mileage.

That timing reduction doesn't stay tho, every time you turn off then start back the engine, the ecu resets it's short term fueling/timing values, averaging in the old values with the long term fuel/timing values. This allows the ecu to run under normal conditions again until it hears knock (if you didn't increase octane or fix the problem since the last start up). The big downside is that if you continually get knock at partial throttle for a few startups (like 5-6 cycles), the ecu's long term value average drops considerably, which negatively affects power output until a proper ecu reset.

Ever notice how your car runs a weee bit better everytime you reset your ecu ? No... it's not in your head... it's your short and long term values being reset... your ecu will then begin the data collection all over again... in the meantime, you get to run on the premium fuel lookup tables.

**The actual on goings are a little more complex, but this explaination should cover the basics. :wink:

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Postby Silvermike » July 2nd, 2006, 9:30 pm

hmm i came to read over this thread... ahhh. im not getting knock. its boost cut! :mrgreen:

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Postby X2 » July 3rd, 2006, 12:17 am

^^What'd you do.. buy a sr20det ?

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Silvermike
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Postby Silvermike » July 3rd, 2006, 3:14 pm

yea, sure.

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Postby X2 » July 3rd, 2006, 3:18 pm

^^ I KNEW you'd finally give into th3 pow3r !!

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Postby Silvermike » July 3rd, 2006, 3:28 pm

^ negro please!

i wont be caught dead driving an ess arrr.

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Postby X2 » July 3rd, 2006, 3:55 pm

LIES !!! ALL LIES !!! :lol:

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Postby Corollaman » September 9th, 2006, 10:02 pm

I had posted this info a while back. But since this is a sticky........

All of my information is taken from:
Engine Management - Optimizing carburettors, fuel injection and ignition systems by Dave Walker

The three most common sources of unwanted noise in an engine are

1. Pinking
2. Knock
3. Pre-Ignition


Pinking -
This is the most common nose of all and it produces a light metallic clinking sound. Pinking is actually caused by the ignition being too far advanced. What happens is that the pressure rise in the cylinder occurs too early and the piston rattles against the bore as it goes over TDC. This is a mechanical rattle that has nothing to do with combustion. Pinking at light load and low speed isn't an engine breaker, in fact it's quite harmless as long as it it not allowed to continue for too long. Since you will gain both power and peace of mind by retarding the ignition at this point, there's no excuse for living with it.


Knock -

Inside the combustion chamber, as the flame front spreads out from the spark plug, a series of reactions take place in the gases ahead of the flame front. We call the gases that are furthest from the plug "end gases" and, under certain conditions, these end gases can auto ignite. In place of the smooth burn, we now have two flame fronts which collide and produce a knocking sound. This noise is much heavier than the light pinking previously described.

Exactly when this knock can take place will depend on many conditions within the engine; mixture ratio; spark plug position; ignition timing; compression ratio and combustion chanber shape to name a few.
The main factor though, is the fuel's ability to resist knock Different fuel additives can reduce the tendency for the end gases to auto-ignite and so the controlled combustion reaches the end gases before they auto ignite.

Pre-ignition

Sometimes referred to as "detonation", this isn't a noise you will have to put up with for very long. Very soon after it appears, pre-ignition will kill the engine stone dead.
Pre-ignition means that the fuel and air mixture starts to burn before the spark arrives. This is caused by something in the combustion chamber getting hot enough to ignite the fuel mixture. You hear a lot of talk about carbon deposits, but for a race engine, it's almost always the spark plug overheating that causes pre-ignition.
Spark plug overheating may be caused by having the wrong plug grade, but it is more commonly caused by ignition timing which is far too advanced and/or a weak mixture. The increased combustion temperature caused by advanced ignition or a weak mixture causes the plug to overheat and pre-ignition/detonation takes place.The plug is almost always the source, even if it isn't the cause

I hope this helps clear things up somewhat.

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Postby Hoddie » September 15th, 2006, 8:27 pm

is it necessary that u hear the knockin sound?
what would be the symtoms in terms of the peformance of the engine?


I'm new to the Trini forums...but usually you won't even hear the knock. It will happen under heavy throttle...and engine noise and exhaust most times drown it out. The symptoms are severe retardation of timing to combat the influx of knock.

^ so when the knock sensor sends the signal to the ecu the CEL will come on?

and ignition will be retarded... by how much?


Usually, the CEL will not come on because of knock...but will when something goes wrong :(

Running a 3.8 liter supercharged engine, my ignition timing directly relates to how much knock is produced. For example, the other night I had some bad fuel in my car, and showed as much as 12 degrees of knock under WOT...at those points my timing was pulled to under 4 degrees bucking the car when it should be at 11 or more. This high knock can do immediate or long term damage to your valvetrain.

Nobody wants that...not even a Canadian.. :wink:

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Postby THE SYNDICATE » July 13th, 2007, 10:00 am

Can turbo'in an N/A engine cause detonation?

I know it might be a dumb question,but still wanted to ask... :|

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Postby X2 » July 13th, 2007, 12:52 pm

typically N/A engines run higher compression ratios (above 9.5:1), so turboing an N/A engine with the same stock ignition timing can invite knock.... but that can be avoided most times by proper engine tuning or even just backing off ignition timing (provided you have enough fuel going in there... otherwise, your knock will turn into Ka-boom)

With the high static compression introduced by turbo's, your tendancy to knock/ping will increase substantially. N/A engines not only have compression ratios that can increase the chance of this, but even unseen things like piston crown shape, crown height, combustion chamber volume, taper and shape and MANY other factors can help invite pinging/knock into an engine that was not manufactured as a turbocharged power plant. All of these issues can be addressed by a skilled mechanic and/or tuner tho.... there is no one definite answer.

That's all the confusing info I can give you for now. :D

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Postby THE SYNDICATE » July 16th, 2007, 8:24 am

Thanks X2...

Hope you can give me some more confusing info :P

Thanks again... :D

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Postby Langdon » November 2nd, 2007, 12:43 pm

i aint want no part

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Postby THE SYNDICATE » November 2nd, 2007, 1:48 pm

:? :idea:

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Postby sidewayz69 » November 14th, 2008, 7:00 pm

eh x2 does de 4g63 engine have ah knock sensor?

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Postby ivar » July 24th, 2009, 12:51 pm

how do you stop it
?

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Postby GEAR_HEAD » July 24th, 2009, 3:21 pm

sidewayz69 wrote:eh x2 does de 4g63 engine have ah knock sensor?


The 4g63 engine does have a knock sensor.

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Postby mistawheela » August 20th, 2009, 12:41 pm

:idea: :x :lol: :? :D

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Postby dreadman » September 1st, 2009, 9:47 am

i have a ga15 engine in my car(fuel injected). whenever i have the a/c on and i driving around 3000rpm i hear some knocking in the engine.....sounding like ignition rattling...what is the cause of this? how can this b solved compared to the other problems noted b4?

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Postby Vinesh » September 10th, 2009, 12:33 pm

nice read

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Re:

Postby 1800GSRLANCER » July 18th, 2010, 7:36 pm

Vinesh wrote:nice read



x2

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