BlownChevy

iTrader: (20)

Just wondering if anyone can explain spark timing and how it "works". Could be an interesting topic dont ya think? Why does a motor make more power with more spark timing? Why does it knock? How does cyl bore size effect the amount of timing that can be run?

dewmanshu

iTrader: (4)

I am out of this one, but this is gonna get thick (in a good way)....lots of info and different angles out there on this stuff. Cool topic, probably one the least talked about items in detail at least when it comes to tuning for it. Everybody always tunes for WOT (or at least talks about it) and nothing much going on for discussion on the part throttle stuff.

TravisH

iTrader: (1)

Geez BC, I'm glad you are starting all these topics, I am learning a lot!

RoninsDenali

iTrader: (1)

Well im no genius but i can add a bit to the topic.

Basis behind spark timing is to adjust the points in which the cylinder pressure achieves its highest point. If you think about things in simple geometry, a piston generates its highest amount of leverage when its motion is a perfect tangent to the circle of motion of the crankshaft. (granted since reciprocating engines travel at such speeds, its actually beneficial to consider its highest leverage point to be just before tangent.)

Since rates of combustion is actually a predictable event, given the necessary variables of Pressure, temperature, air fuel ratio, etc. Adjusting the point in which the engine starts the ignition of the combustion mixture achieves more power by moving the point of maxiumum cylinder pressure closer to the point of maximum crankshaft leverage. More conservative spark tables the max cylinder pressure would occur after maximum leverage.

Hmm, i understand it, i hope its not too much of a mess for everyone else to understand my babling lol.

MikeGyver

iTrader: (5)

And the rate doesn't change, but the rpm does. So there is less time for combustion to complete as rpm increases. Therefore, for max power, to get peak pressure at the correct crank angle, the spark is retarded at low rpm, and advanced at high rpm.
Next commentator, please.

1slowsilverado

iTrader: (1)

Without going off topic lets take a basic look at whats going on inside the engine to get a better understanding of spark timing. There are six key things. Intake, Compression, Spark, TDC, Combustion and Exhaust.

Try to visulize if you can.

The piston goes down from TDC, Intake valve opens and sucks in the charge. The Intake Valve close and piston returns to TDC compressing the Charge. When the spark plug fires it burns the fuel mixture. The temperature rises and the fuel is converted to exhaust gas. The transformation causes the pressure in the cylinder to increase dramatically and forces the piston down. This is called the power stroke.

Now to get the most power from our engines we need to maximize the pressure in powerstroke. This is where spark timing comes in. Things happen rather quickly and there is a delay from when the spark plug ignites the mixture and cylnder pressures are at there maximum. The spark should occur before the piston reaches the top of the compression stroke, so by the time the piston starts down into its power stroke the pressures are high enough to start producing useful work, Work = Force * Distance.

Timing is important and can be advanced or retarted depending on conditions. Fuel burns pretty quickly but as engine/piston speed increases so must spark advance.

There are many other factors like engine design, flame kernal, detanation...etc

Here is a nice read everyone.

https://ls1tech.com/forums/showthread.php?t=254868

BlownChevy

iTrader: (20)

So far so good.....Next question: Can you run more spark timing with a large bore or small bore engine?


BTW this is for discussion, I know the answers I just think posing these questions may provide others with a wealth of knowledge that is sleeping / trolling on this site.

Okie5.3

iTrader: (1)

Generally the larger the bore the more timing required because it takes the flame front longer to make its way across the bore. Timing for smaller bore is just the opposite.