no, i cant hear it. I scan the motor using HPtuners. the 24 degrees is the commanded. if it pulls timing due to knock it drops below even that, and it will tell me how many degrees, usually only 1. it just shows up as a display saying how many, if any, degrees was pulled per table cell

 

Back to the detonation stuff... I found this while on David Vizards site it is a little long but is at least in my eyes is a good chemical (Its probably easy for you but I had to read it a few times) explaination of detonation

In a running engine, air is drawn in at some ambient temperature, and this
air then begins to pick up heat from the hot internal engine surfaces it
contacts. Finally it enters the actual cylinder, where is it heated by even
hotter surfaces. Trapped there, it is heated again by the process of
compression.

In this heating process, some little discussed chemical reactions begin to
occur in the fuel. Called preflame reactions, these take the form of slow,
partial breakdown of the least durable types of fuel molecule. Fuel
hydrocarbons have three basic forms; straight carbon chains, branched
chains, and ring structures. Temperature is a measure of average
molecular activity, but there are always some gas molecules moving
significantly faster than the others. These faster moving molecules hit and
break some of the less durable fuel molecules, dislodging some of their
more weakly bonded hydrogen atoms. This released hydrogen is very
reactive (normally hydrogenous travel in bonded pairs, but his is atomic
hydrogen) and instantly pairs with an oxygen from the air to form what is
called a radical, a chemical fragment that is highly reactive because if
contains and unpaired electron. Its attraction for the missing electron is so
great that it can snap one out of other chemical species it happens to
collide with, thereby breaking it down as well.

At some point in the compression stroke, the spark ignites the mixture and
combustion begins. The burned gases, being very hot, expand against the
still unburned charge, compressing it outward into the squish band. This
compression rapidly heats the unburned charge even more, accelerating
the preflame reactions in it. As a rule of thumb, the rate of chemical
reaction doubles every seventeen degrees F. All this while, the population
of reactive molecular fragments radicals is increasing in the unburned
endgas. If this process of heating takes long enough, and reaches a
temperature high enough, this population of radicals becomes great
enough that its own reaction rate one radical creating more and more
through further reactions accelerates into outright combustion. This is
autoignition.

Now why does this heated, chemically changed endgas detonate instead of
simply burning? The fuel in the endgas is no longer ordinary gasoline. The
preflame reaction that have taken place in it have changed it into a
violent explosive much like a mixture of hydrogen and air, or acetylene
and oxygen. It is in a hair-trigger state, being filled with reactive
fragments from preflame reactions. When it autoignites spontaneously,
combustion accelerates almost instantly because the material is so easily
ignited now. The combustion front accelerates to the local speed of sound,
igniting the material it passes through simply by suddenly raising its
temperature, through the shock wave it has now become

 

I guess you can look at it this way: (and to be honest, i had overlooked this fact in my posts as well)
advancing timing is typically done to keep up with a rapidly spinning engine. you advance the timing so by the time the spark takes full effect the motor is at TDC and you get the most out of ur burn. So yes, at low rpm u need very little timing because the motor is moving slowly. as you increase rpm the timing SHOULD be able to increased in a linear fashion. however, as you start making heat at higher rpm the timing needs to be backed off. to be honest i dont fully understand why the timing affects knock, i just know this is what we do.

also, the decrease in my timing curve is a little exaggerated because I run nitrous. most cars will level off or decrease slightly. the 8ish degrees that I decrease is a little more than most NA cars will do.

 

Source of the artical http://www.gofastnews.com/board/engi...rn-rate-4.html

This stuff is facinating it is truly very complex with tons of variables.... The old school thought of colliding flame fronts does not seem valid any more it is a separate explosion not a burn. It actually seems to give a little validity to the singh groove theory of altering the squish zone to promote turbulence (and theortically certon chemical concentration.

 

the main contributor of the heat is compression. last year i could have told u off the top of my head how to calculate temp changes in a piston-style system but my brain shut off after finals lol.

this doesnt sound accurate to me..... radicals are extremely difficult to make. for example, the mass spectrometer uses a heating coil, a vacuum, and an extremely high voltage differential to produce ions by knocking off electrons and fracturing the molecules. hydrocarbons rarely fracture at just a C-H bond.
http://webbook.nist.gov/cgi/cbook.cg...s&Large=on
thats a mass spec of octane. if what that paragraph was saying is true you would expect more signal around 113 mass/charge. most of the signal corresponds to larger sections of the molecule, which would be expected because the very small size of hydrogen makes it a very unlikely candidate for removal. the larger carbon is much better suited for taking on charge. the part about the faster moving particles IS true, but you typically wont have them knocking hydrogens off..... thats the kind of info that chemists see and its like fingernail on a chalk board to us... it may make sense on a certain level, but in reality its just really really wrong. it makes me cringe the more i think about it lol.

also, the radical he talks about would have to be HO2, which.... doesnt exist as far as i am aware.... radical reactions are a very special part of chemistry which are usually used in chain reactions like polymerizations. if i was looking at a system, radicals would be one of the last things i would look for for an explanation. most of the time, if you make a radical it will just react with another radical to neutralize charge.
once again, this looks like sound reasoning, but it just doenst make any chemical sense. the combustion of gas is extremely exothermic. tons of thermal energy is released per molecule combusted. the energy released is sufficient to ignite neighboring molecules. So yes, the ignition starts at the spark plug, but he almost sounds like hes saying that ths end of it, and its just used to compress the rest of the gas. this isnt true. I like the link slvr posted for this part. think of the combustion as ripples from a stone into a pond. as heat is released it ignites the neighboring molecules, which in turn ignite their neighbors. ive never heard of a squish zone...... [&:]

this is the part where i said, earlier, that kinetics wasnt an issue. the speed of the chain reaction WILL be temperature dependant, but honestly there is enough heat released that the temps wont matter. and if an oxygen and fuel molecule find each other and there is sufficient energy to combuts, for all intents and purposes, the reaction is instantaneous.

[:@] OW... OW [&o]
I looked this guy up on google... apparently he is a writer for sports cars? well, hes not a chemist.
"detonation" is not a word which describes the MANNER in which the fuel ignites. there is nothing about a radical that would make it more prone to combustion, in fact, the high energy state of a radical would make its termination reaction endothermic, i would think.... this would ROB energy from the system. this last part is just science fiction, plain and simple. detonation, rather, describes the time in which the ignition event occurs. if its not when we intended for it we call it detonation or pre-ignition (depending on before or after).

now, its a very ATTRACTIVE answer, because it sounds like it would work, and sounds very official.

but... shock-wave.... speed of sound.... [&:] a shock wave wont add heat energy to a system... its a pressure front.

 

Spec, what is different about your type of (computer controlled) engine where the timing needs to be "backed off" at higher rpm's?
Distributors on old-school engines, such as mine, achieve full advance at a given rpm and stays there even as the rpm's climb.
And to your "to be honest i dont fully understand why the timing affects knock" question, are you asking the correlation between timing and knock?
Knock is caused by the detonation of fuel when it occurs way too soon before TDC. Basically, the fuel fires and it is trying to push the piston back down while it is still on the up-swing.
The "knock" is the resulting sound. And obviously, too much of that kind of treatment isn't good for the engine.

 

I dont know what the difference is. the MSD fuel curveswere from an ignition controller for a carb swap for ls1s. in fact I dont even know if those curves are appropriate. either way, timing does not increase linearly with rpm as you would expect it to

and no..... i understand the correlation, but knowing a correlation or trend doesnt mean you understand the fundamentals. detonation occurs when the mixture gets heated above its auto-ignition point. and yes, then it happens typically before TDC. as far as the CAUSE, all I can come up with is the spark occurs way too early and some of the energy of the ignition goes to pushing against the crank, in which case it would happen every rotation.

however, the kindof detonation weve been discussing has more to do with auto-igniting fuel, rather than spark-ignited. and in that sense, no, i dont know why an earlier spark would increase the likelihood of an auto-ignition

 

Heat is a big enemy. Not just to the fuel mix, but to the internal components as well. If the combustion chamber is running hotter than it wants to be, different things can happen. Say you had a build up of carbon on the pistons or the head. Those spots could start to glow and combust the fuel before the plug even fires. Or your plugs could get so hot as to start to act like glow-plugs in a diesel engine. Ever have an engine "diesel" on you after you shut it off? The engine can stay running (usually just a second or two) on it's own, even with the ignition switched off.
I had that happen to me once with a Chrysler 4 cyl. carbureted engine. The ignition timing was too far off, making the engine run a little hot. It would "diesel" just a little when I shut it off. One time I said "I'll show you a thing or three" and pumped the gas pedal rapidly as it dieseled. I figured I would flood it out! Uh-oh! The engine started running BACKWARDS on it's own, with the key OFF!! Scared the crap out of me, because I couldn't shut it off by putting the auto trans in gear (torque converters don't grab while going backwards you know). The engine was running for a good minute on it's own, and I was trying frantically to think of a way to shut it down. Not to mention, according to the gauge, now the engine was really getting hot! I finally got it to quit by taking a vice-grips to the fuel hose to cut off the flow.
So, given the right (or wrong) conditions, an engine doesn't even need ignition spark to run.

 

Believe me David Vizard is very well respected in the engine building field but I dont think he wrote the chemical explaination it was in a post that made sense to someone like me lol. My timing controll is very similar to Camaro 69. The squish zone is where the piston "meets"the flat area of the combustion chamber basically it promotes turbulence for a better burn.I think I have another chemical explanation somewhere It does seem that the general belief now is that detonation is a separate explosion of sorts. Ill find the other post.

 

When I worked for a coal company the mechanics would tell me the old diesels would do that they said it would burn them up although I think the old dietroits would run either way(2 cycle diesal) I think GM eh had a engine on the drawing board that was gasoline that is supposed to cuise with no spark like a diesel. Here it is http://money.cnn.com/2007/08/23/autos/gm_hcci/ Thanks for the laughby the way lol...