Whoa!!!! Not trying to be an ass, but I want to post and clear a few things up that I found to be very incorrect and could potentially harm peoples engines.....
1st, afrs and timing are very much so related. You say they are not simply because the air/fuel mixture is already injected before the spark ignites it, therefore there is no way that timing changes this mixture? Well, the afr your wideband is reading IS NOT the air fuel ratio that was initially injected, it is the ratio after it is burnt!! If your timibg is way advanced, you wil burn more or the fuel in the mixture thus running more lean, and vice versa. Changing timing often times, calls for an adjustment of afrs be made. You said it yourself, for performance tuners, afrs are used as a temperature control, so to speak. Meaning, if the engine is running hot in a certain region, it is because of one of too things: 1.) too much timing advance, or 2.) too lean of an afr.
With that said, you can also richen up your afrs to make a motor run cooler due to advance timing. If there is slight detonation, you can fix it by adding fuel, or pulling timing, either or depending on the severity of the knock/detonation.
2nd problem I have with the info posted, is in the detonation section. There is not one word in there that describes detonation. Detonation is post spark, not prespark. You are referring to preignition, which basically is when a hot piece of carbon or hot/glowing/melted spark plug electrode causes the air/fuel mixture to ignite before the spark plug ignites it. This usually happens at 180* bdc (bottom dead center) of the intake stroke or 160* btdc (before top dead center) of the compression stroke. It usually ignites well before tdc, which causes EXTREME heat on the piston as it pushes up the entire last stroke against already burnt and expanding gasses caused by this precombustion. Preignition should not he taken lightly and will usually destroy an engine within seconds with no signs or symptoms, and usually on the first occurance as well. Usually it melts the piston, but is known to also melt the spark plug electrode and even the exhaust valves at times. Ways to prevent it are to use proper plugs. If you make alot of power, have higher CR's, are boosted, etc...use colder plugs. If you decide not to use colder plugs, tune accordingly to your stock plugs, meaning dont let your plugs get to hot to the point that they become a preignition source. Most if the time 1 or 2 steps colder helps. Rule of thumb on modified motors is to run the coldest plug you can that never will foul on you. If you need more in depth info on preignition and plugs, pm me.
Detonation is the more common term heard when speaking of tuning timing. The correct definition of detonation is when the unburned "end gas" ignites due to too much heat and pressure in the cylinder. Detonation occurs AFTER the mix is ignited by the spark plug. Detonation is definately something to worry about, but nowhere near as severe as preignition. Detonation usually breaks things if severe enough, such as ringlands, and it often pits the outer crowns of the piston and is also known to pit the spark plug. So another rule of thumb....if it's melted, its preignition, and if it's mechanically broken, its detonation. The famous pinging sound you hear from detonation is from the structure of the parts in the engine that actually ring when this detonation of the end gas occurs. Detonation is pretty much a secong explosion in the cylinder, and it WILL break things because it creates a very large spike in cylinder pressure when it happens. Depending on the motor setup, you could run with detonation of seconds or months, it all depends. Another sign of detonation besides the famous pinging, like i said before is pitting of the spark plug. it will even sometimes have silver flakes on it, in which case is very bad because that is probably peices of the piston that broke off during the detonation.
What causes detonation? Several things do such as CR, cylinder size and shape, spark plug location, etc.....but those are already engineered into the motor so no worries there. The reasons you want to worry about are timing, afrs, and fuel octane. Too much timing advance causes detonation because it ignites the a/f mixture too soon, this basically lets the cylinder build too much heat and pressure, which causes a spontaneous second combustion of the end gas I spoke of earlier. Too little fuel cause more heat, and more heat causes a spontaneous second combustion of the end gasses. Too low of a fuel octane allows the end gas mixture to resist combustion poorly, causing a second spontaneous combustion. I could go more in depth upon request......but it serves a good purpose to understnd what is happening and why, when you alter things in your ecu.....aka, tuning.
Putting all of this together, one can EASILY see why afrs do correlate to timing. If you make too much heat, then you need to remove it. Either add fuel or pull timing, OR use higher octane gasoline....
for questions pm me, i am very willing to help out on this thread for street tuning, and not so much dyno tuning
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