Its not detonating! How is it hurting it? If you could clarify mabey I could understand what your trying to say. Its running great, and not by the ass dyno but by the dragstrip timers.jonny-vtir on Sep/21/02 said:You should never, I repeat NEVER go past 18 degrees BTDC, unless you have an extremely hard tuned all motor, and even then your taking a risk. Plus you won't get any realistic gains past this point, especially if you want your motor lasting more than a week. As for the knock sensor I don't know. Advance it to 18 BTDC for street and track and leave it at that.
yeh, thats what i was thinking, because even w/ the valves adjusted, I know my b18b has a fairly loud valvetrain @ 6800 .lolFentoozler45 on Sep/21/02 said:Just a side note... To my understanding, the factory knok sensor included in the B18C1, B18C5 is little more than a microphone. After 4k RPMs(I think it was 4k) the knock sensor is unable to distinguish knock from normal engine sound.
Thats a good article, but if its not detonating and the engine is obviously making more power (times at track, or more importantly trap speed) then It cant be sparking too early. Right? Ive got a pretty potent ignition so the increased cylinder pressure is welcome. I feel like, running 93 octane, I should be safe no matter what the load on the engine. You imput is welcome and appretiated, and It probley needs to be discussed more for anybody else that needs to know.kelly on Sep/21/02 said:
Detonation; Knock; Ping; Pre-igintion. You hear these terms mentioned all the time, so we might as well straighten them out.
Let's get pre-ignition out of the way first. Nothing mysterious about it. The A/F mixture (intake charge) explodes before the spark plug fires. You would figure the intake charge would have to get pretty hot to do that, and you would be right. The pressure from a high compression engine is enough to generate that kind of heat. (In fact, diesel engines are designed to fire on the heat from compression alone.) Higher octane fuel is the antidote, so in general, a higher compression engine will need higher octane fuel.
Cramming more intake charge into the combustion chamber has the same effect as raising compression, so in general, the higher your boost, the higher the octane requirement to avoid pre-ignition. Finally, premature inflagration occurs more easily if the intake charge is hot when it enters the engine. This is why larger intercoolers add a margin of safety in forced induction engines--at least until you turn up the boost.
Another cause of pre-ignition is a hot spot in the engine. Maybe some of those carbon deposits are glowing red hot. Maybe the spark plug itself is hot enough to ignite the mixture before firing. This is almost certainly the case if you have ever experienced a car that kept trying to run after you turned the key off.
The more tricky term is "knock." Although most of us prefer to talk about "detonation," it turns out that "knock" is the correct term as used in automotive texts.
"Detonation" is actually slang, and "ping" is not a well defined term at all. That having been said, I will stick with the term "detonation" for this discussion.
"Detonation" differs from pre-ignition in that it occurs AFTER the mixture starts to burn. Normal burning involves a flame front--a relatively slow, controlled explosion--which marches along in a calculated fashion. As you would expect, normal burning raises the pressure in the combustion chamber. Sometimes this is enough to get the last bit of intake charge (called the "end gas") so excited it explodes before it is supposed to. It is a very hot explosion, on the order of ten times the heat of controlled combustion.
But there is more to it than that.
If you graph the amount of pressure in a combustion chamber during normal burning, it shows a relatively smooth event. The occurrence of detonation shows up as a sharp spike on the graph--a sudden shock wave if you will, with pressures on the order of several thousand psi. The duration and strength of the explosion is too fast to contribute to the rotational output of the engine. Like a slap in the face, the full impact must be absorbed within the combustion chamber itself. Damage is most likely to occur at the weakest points--namely the piston pin and piston crown. Piston engines designed for high stress situations can have the piston rings further away from the crown of the piston. The shock of repeated detonation will eventually weaken anything it can, and the heat generated will take care of the rest.