I've never really understood what timing is all about. Can someone explain the role it plays in the optimal functioning of an engine, and what the numbers mean (28 degrees of timing, etc.). How does more timing increase performance, and why? It's pretty embarrassing that I don't know this, and I'd love to get this cleared up once for all. Thanks.

 

Hope to clear this up for you. Ignition timing is what I assume you are referring to. Anyway... when the spark plug fires and lights the fuel mixture, it takes a short time for the flame front to burn all the fuel as it travels accross the top of the piston. The fuel as it burns creats heat and expands forcing the piston down. Ideally you want to have the fuel reach its highest energy potential when the piston reaches about 15 degrees after top dead center. Timing is referred to in degrees of crank shaft revolution, on revoluion is 360 degrees. So using the #1 piston as the reference, when it is at the top most part of its stroke, 15 degrees advance would mean that the mixture fired 15 degrees before the piston reached its highest position. High test fuel burns slower but with more control than regular, so for high test you need to run a bit more spark advance. As the engine speeds up, it is spinning faster and faster, so to account for this, the ignition is fired sooner and sooner to keep the burn at the optimum. At some point years ago they found out there is a point of diminishing returns and they actually start to retard the timing a bit, somewhere in the 5,000 RPM range. What few people realize when they put a cam in and are looking for TDC (TOP Dead Center) is that the piston actually comes to a stop for several degrees before the actual TDC and remains stopped for several degrees after TDC before it starts to travel down the cylinder again. When degreeing in a cam, you have to use a piston stop and degree wheel so you can find the exact TDC point, otherwise you can mistakenly be off one tooth one way or the other.
If the mixture receives too much advance, then you can reach the high point of the power before the piston is at the right position and you hear the pounding as the piston is trying to go up while the fuel mixture has ignited and is pushing down, sometimes you get a violent explosion and set up two flame fronts that collide violently. There is a difference between preignition and detonation, but to the Knock Sensors they are bad and for that reason they are programmed to pull back the timing to a point where it no longer senses detonation. It may even switch the ignition map from the high octane to the low octane map which reduces power but should eliminate engine damaging preignition or detonation.
I hope this has not confused you and has possibly shed some light on this matter.

 

Awesome stuff, and you explained it so well I don't even have a follow-up question. I appreciate you taking the time to help me.

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