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How to determine knock/ping/detonation


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12 replies to this topic

#1 Phaedras

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Posted 11 January 2005 - 01:41 AM

This may sound stupid, but I have no clue as to how to determine any of these phenomenae.

My motor seems to be running relatively fine, according to my ears, but I don't know what I should be listening for.

#2 tizzle

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Posted 11 January 2005 - 01:54 AM

It should sound like shaking a can of marbles, heard under load or acceleration

#3 Ross

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Posted 11 January 2005 - 02:09 AM

And if you think you can hear it, stop whatever is causing it immediately. detonation/pre ignition can cause seriuos engine damage very quickly.

#4 phishy75

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Posted 11 January 2005 - 02:37 AM

if it was bad anough to be doing any serious damage you would definitely know it to hear it - it sounds like bad rattling when under load.

#5 Myxalplyx

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Posted 11 January 2005 - 03:34 AM

There could be other things that sound similar to it. Just like Phaedras, I still do not know what pinging would sound like. People say like a can of marbles but I've heard this sound in one of my XT6s before and was told that it wasn't pinging.

I posted a video of it at the XT6.net site:
http://www.xt6.net/f...ghlight=pinging
but have since taken it down. It sounded just like small firecrackers going off as I was approaching 85-90mph. Air/fuel ratios was getting leaner and leaner still since the intake is routed out through the passenger side foglight.

I guess you'd have to hear it at least once to know what it really sounds like. I am not looking forward to hearing it....EVER. :brow:


Here's another video from the thread I posted above. A guy responded and said you could hear pinging in his XT turbo.
http://x35performance.com/xt/100_5068.MOV *Save-As*

#6 All_talk

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Posted 11 January 2005 - 10:45 AM

It’s something you kinda develop an ear for and requires good high frequency hearing. When its severe most people can hear it and feel the accompanying power loss, it sounds like a diesel engine on cold start, a kind of clatter. At lower levels you cant hear it but it still can do damage.

And a couple of definitions: Detonation is when the flame front in the cylinder is supersonic. Pre-ignition is when the burn starts in two or more places (one is normally the spark plug) and the flame fronts collide. Both conditions move the cylinder pressure peak before TDC instead of just after, this creates extreme force on the piston (and everything else).

Gary

#7 Ross

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Posted 12 January 2005 - 12:14 AM

Pre-ignition is when the burn starts in two or more places (one is normally the spark plug) and the flame fronts collide. Both conditions move the cylinder pressure peak before TDC instead of just after, this creates extreme force on the piston (and everything else).

Gary


With pre ignition, its not just the higher pressure that does damage. Most damage is caused by the resulting shockwave from the two flame fronts colliding. Hence the noise and the impact loading on the head and pistons.

#8 archemitis

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Posted 12 January 2005 - 01:58 PM

to me it sounds like a gremlin in the engine with a ball pin hammer.

only at, or close to full throttle, and mostly under load

#9 Snowman

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Posted 12 January 2005 - 06:05 PM

I seem to notice a LOT of carbed EA82 subarus making what sounds like a ping/knock noise on a pretty regular basis. If that was the case, I would think they'd fall apart in short order, but nothing bad happens. Is the noise something else?

#10 archemitis

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Posted 12 January 2005 - 06:54 PM

lifters? exhaust leaks? i dont know why a carbed ea82 would ever knock.

#11 85Sub4WD

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Posted 12 January 2005 - 08:52 PM

My carbed EA82 pinged quite often, especially under load. I agree with Snowman in that I am surprised it didn't fall apart, but who knows? Subarus are rugged cars, and an aluminum block would absorb the shock much better than a steel one because steel is much more brittle. I found that timing wandered on it so I had to set it quite often, and if I did that, it would not ping. I tried several different distributors in it and found that that was a consistent problem. Usually you should not have any problems if you timing is correct, you are burning the proper gas (mid-test (90 octane) or better), and your engine is not full of carbon deposits (run something through to clean them out). Absolutely lugging the engine will make it ping/knock and do a bunch of other bad things (like hurting your piston rings/head gasket) - don't do it. If it is not fuel injected and you are mechanically/electrically inclined, convert it to SPFI. It is relatively easy and offers substantial performance gains without sacrificing economy.

#12 Ross

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Posted 12 January 2005 - 10:53 PM

I know the sound you talking about, but i dont think its knocking. An aluminium block will not take more hammering the a CI one. yes, CI is a lot more brittle, but is also stronger, and has better fatigue properties. The pistons in htese engines are also nothing special, and these are often the first things to break under knocking. Maybe the sound is simply lifters, or valve slap.

An aluminium block, and especially aluminium head does reduce the tendency for knocking to occur, as it transfers heat much faster than CI.

#13 Snowman

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Posted 12 January 2005 - 11:32 PM

I'm amazed more people haven't noticed this. Maybe our gas here sucks or something. My car has had lifter problems, and it's not that. The sound accompanies load/throttle just like preignition. One of the engines that I tore down had been known to have a propensity for making the noise, but there was no indication of damage to the rings, pistons, head, or even the spark plugs. Very confusing to me.

I have found that my car almost never does this now that I have converted to SPFI. Maybe it is associated with the older-style disty that is used on the carb cars?




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