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reading through the posts i have come across people talking about knocking levels high and low can someone clear this up for me and tell me what it is.,.,thanks:wavey:
 

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To understand what detonation is, you first have to know what is going on inside the combustion chamber. I should hope that if you are interested enough to read this article that you would already know such things however I will go into it a little bit. Detonation occurs during the power stroke, this means the piston has returned to the top, compressing the gas and fuel mixture, the spark plug has ignited this mixture and the piston is now on its way down. This is what makes the engine run, hence, ?power stroke?. During a normal power stoke, the spark plug ignites the fuel, which burns creating pressure in the cylinder which forces the piston back down again. The ideal way for this to take place is not in an actual explosive form, but more like a whoosh. Think of the effect you would have on a piston by smacking it with a hammer, you could give it a good hard whack but it chances are it wouldn?t travel very far, and also receive some damage in the process. Now, think of your hand pushing the piston down with even force the whole way to the bottom, you wouldn?t have as much energy released in a single moment like you would with the hammer, or explosion, but you would sure get a lot more power over the entire stroke.

Ok, so, now you know what happens during the power stroke of the engine, and the ideal conditions of that power transfer. Detonation, sometimes referred to as a knock, occurs when the air fuel mixture in the combustion chamber burns abnormally. By abnormally I mean in an explosive manner. If you could some how slow down the burning of gasses in the combustion chamber, you would first see the spark plug fire igniting the gasses. These gasses would begin to burn outward filling the combustion chamber and forcing the piston down. Late in the cycle, but before the flame has reached the cylinder walls you would see small, bright flashes of light in front of the flame front. This is the last bits of the air fuel mixture burning by them selves in an explosive form. In fact, the tiny explosions that make up detonation can burn at the local speed of sound. This creates a shockwave that hits parts and makes them ring audibly, and can even in the worse case, blast heat-softened aluminum out of pistons or the head.

The physical cause of detonation in the combustion chamber is the prolonged or excessive heating of the fuel and air, which breaks down the molecules into a form that can ignite by them selves, and then burn with tremendous speed. Higher compression ratios, resulting from turbo charging or super charging and engine, or introducing extra oxygen into the combustion chamber by running Nitrous, are usually to blame for detonation. However, even naturally aspirated engines running high compression ratios are not immune to its effects. Normally, compression in these engines is raised to just below the point of detonation or to the point in which it is simply not efficient to tighten the combustion chamber any further. This is where higher-octane fuel is used. The higher the octane rating in the fuel, the slower it burns, and thus is less receptive to being changed into a auto-ignition state.

Now, you probably want to know how to check for detonation. Besides using your ears, you can also read the spark plugs. You may want a magnifier and the brightest light you can find, perhaps the sun is a good choice. What you are going to be looking at is the center wire of the spark plug. You want to do this test with a pretty fresh set of plugs that have been run hard for a short time. First check for deposits on the center wire, if they are there and have not been blown off, you?re in pretty good shape. If you run the engine hard and the wire looks completely bare but still resembles a new plug in good shape your getting close to detonation. When the edges at the end of the center wire become rounded, like a broken glass rod you are at risk for some serious engine damage. Remember, this is to be done with new plugs, of course a plug with 50k miles on it will start to round off from normal use. Do not mistake this for reading the plugs insulator. That is for judging the fuel mixture. You can also see the affects of detonation inside the combustion chamber itself. This comes in the form of sand blasting usually on the edges of the piston, a matte finish look instead of the normal light tan or cream-colored deposits. This is the same thing that makes the center wire of the spark plug rounded. Another symptom of detonation is the rise in temperature of engine coolant. This is caused because as detonation occurs it blasts away the tiny film of stagnant gas that sticks to the combustion chamber surfaces. This film, sometimes called the boundary layer helps insulate the chamber surfaces from heat. Without it, more heat transfer takes place between the cylinders and coolant.

Do not confuse detonation with pre-ignition. I am also currently working on an article to explain that as well
 

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Discussion Starter #3
bloody hell, fantastic read .,.,thanks


so what are knocking levels lol::chuckle: :chuckle: :chuckle:
 

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Knock

v. Good article,

Knock level is how much of that audible sound (described above) is picked up by the knock sensors.

Therefore the higher the level of knock = higher levels of detonation in the engine that have been detected. Indicating your have a problem with fuelling / ignition. High deteonation can / will lead to a knackered engine or melted piston(s). Not somewhere you want to be.

The Skyline knock sensors are supposed to be reasonably accurate and if you have a PFC you can pick up the knock levels on the hand commander. From experience the PFC can and at times does pick up other sounds that show as knock at unusual high levels. Btu these have been on very few occasions.

The knock level on the PFC on average should be under 40 as a rough estimate. I am not sure how other knock meters wil display knock and what a safe level would be.

Kev
 

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really great read - this should be a sticky.
yep, on hard accel. in my gtst which has a pfc, some breathing goodies (exhaust, induction, downpipe) and the boost set to 0.8bar I generally get values around 12-17 ..however I currently have some nos octane booster in my full tank o vpower and I decided to advance the ignition +4 degrees to get the best from the octane.
On hard accel. taking the car through all the gears in the revrange I ended up getting a knock count of 83! Unfortunately I never got to check this on the graph as I were too busy watching the road eeeeeeeeeekkkkk I'm going very fast!!!!
I absolutely cacked myself and I've since tried a good few times and not got close to that value but then I haven't advanced the ignition either in my last few drives so I'm guessing the advance had something to do with the high knock count.
Since driving hard without the advance the car has been as it was ...12-17count. Weird thing is my ecu light didn't flicker once during that hard 83count run. Chances are it was a count of 33 hehehehe (my knock warning level is 35) :p
 

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fantastic read! taht really taught me as well!

best discription of det to listen for is :

if you can imagine a flat piece of glass, and someone dropping lots of tiny pins
onto it.
i fyou hear that, then worry!
 

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carterjohn,

Nice read, however it sounds like a cut and past from an old American magazine.

I think you'll find most serious tuners on here use elctronic listening devices as they will let you know the problem when detonation is starting to happen not after signs of damage are showing up on the plugs.

If you know when it's happening you can alter your map, speckles on the plugs what do you do next. back off the ignition or richen up the fuel.

Add in a wideband lambda and you know which map to adjust.
 

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i never claimed i wrote it m8,and its from a website im a member of.

i just thought it was a fantastic piece of information and deserved to be shared with this website.
far from trying to mislead anyone,i was trying to help members here.

not everyone has an apexi fitted,or has the cash to pay tuners.
it was meant to help out fellow enthusiats.

i have owned and destroyed many jap cars over the years,so i take every single piece of advice on board.
 

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i never claimed i wrote it m8,and its from a website im a member of.

i just thought it was a fantastic piece of information and deserved to be shared with this website.
far from trying to mislead anyone,i was trying to help members here.

not everyone has an apexi fitted,or has the cash to pay tuners.
it was meant to help out fellow enthusiats.

i have owned and destroyed many jap cars over the years,so i take every single piece of advice on board.
carterjohn,

As I said above, it was a nice read, but does not represent current tuning practice due to the step change in electronic circuit development over the last 10 years.

I would hate any budding tuners to think that the only way to observe det is by looking at plugs showing the signs of the onset of engine damage.
 
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