Originally Posted by Marcus Frost

I am amazed at the recent influx of people who, at least, claim to do tuning and at the same time are willing to carry on open conversations regarding the same topic. They will notice that in the Benz world, things are kept under lock and key and us, the public, are given a bucket of fish heads every so often to keep us happy. I applaud them if they are, in fact, who they say they are and continue to contribute to this forum.

With that said, the modifications that we do to our cars are so simple and straightforward compared to other tuning platforms that it is really much easier to talk about timing/fueling/etc. You take a platform like the GM LSx platform, that can go from monster cam, to twin turbos, to a blower and spray... you have yourself a real wide array of tuning approaches/etc.

With that said, the question at hand here is what is safe... and I think what people are really asking about is how ignition timing works - because what is safe is really a secondary question if you do not understand ignition timing on a rudimentary level. The explanation to that is somewhat complicated but not so much so if someone is trying to understand it at a fundamental level. In a few words, ignition timing in our modern cars (please note, mechanical timing is different in execution, but applies the same) is basically when your ECU tells your ignition system when in the combustion cycle do you want to ignite your air/fuel mixture. You are shooting for exactly the point where the combustion will deliver the highest amount of energy possible to the piston in it's downward stroke which thus turns the crankshaft and applies power through the transmission to the wheels.

Excessive timing advance, that is, sending the spark too far ahead of time is very dangerous (timing retard, while not as dangerous, can also cause problems). One of the major reasons it is dangerous is because if you ignite the air/fuel mixture too early before the piston reaches top dead center (TDC), you are actually exerting a force on it that opposes it's movement upwards. This force can cause failures on any number of parts and can destroy just about any engine, no matter how "tough" it may be. We have knock sensors on our cars which allow for the ECU to "hear" when the engine is "knocking" - knocking occurs when the combustion process goes awry, so to speak, as it will generate vibrations due to a number of erratic circumstances... such as preignition, detonation, etc. When the ECU "hears" knock, it will typically pull back timing because that is a very effective way of "relaxing" the engine and the stresses during the combustion process as to protect it from the failures I mentioned earlier.

Think of what happens to a baseball when a pitcher throws it towards batter, and the batter connects with the ball using his bat. The ball deforms drastically as the force applied by the bat transfers to the ball and changes it's direction... unfortunately pistons are made out of metal and they are not as pliable as baseballs. That "crack" you here when it makes contact - think of it as "knock", a LOT of it.

As I had mentioned previously, there are many factors that can dictate when in the combustion process ignition should occur, and the reality is there is no "definitive answer". These sort of discussions, though, do help a healthy discussion on what "works" and what "doesn't". I think that's the real question to ask, and it's one that Velociabstract has answered.

-m