plug gap with Dyna and Accel coils/wires?

Here we go again. Octane has nothing to do with burn rate. I don't know who started this roomer and wen.

otakar wrote: Here we go again. Octane has nothing to do with burn rate. I don't know who started this roomer and wen.

Octane is the RESISTANCE to flame ignition/burn, correct?

Octane is the ability to prevent auto-ignition under given temperature and pressure. "Octane" is actually a Hydrocarbon which is used as a standard for this measurement. 100 Octane means that a given fuel/hydrocarbon has the same ignition properties as actual "Octane" but not necessarily the same burn properties. Aviation fuel for example comes in octane ratings from 87 to 130 but all of these burn much slower than automotive fuels. Racing fuels burn faster than "pump" fuels. No matter what octane they are. "Nytro" for example, has a very LOW octane but burns extremely quickly. 130AG has a very hi octane but burns very slowly. These fuels are engineered for engines that operate at different RPM ranges. Aviation fuel for example must be able to run in engines that have a sustained RPM range of 1800 to 3500 RPM

D'oh. Otto beat me to it.

Not really resistance to ignition, but more properly resistance to premature ignition.

Premature ignition is ignition from a source other than the spark or the flamefront created by the spark.

The premature ignition can acutally take place after the spark. This sounds contradictory, but is not. When the flamefront starts, the gases expand, compressing the un-burnt gases elsewhere in the cylinder. If those un-burnt gases ignite as a result, that is considered premature because it ignited before the flamefront reached it. Octane is used to prevent that premature ignition, but it has little to no affect on the desired ignition of gases at the flamefront.

Premature ignition (I think) is where the term pre-ignition comes from. When there is enough pre-ignition happening in the cylinder, you can eventually get what is called detonation, which is what hammers the piston. Knock and ping are words used to describe the sounds, but I'm not sure those words are as closely defined as pre-ignition and detonation.

I thought "auto-ignition" and "premature ignition" meant the same thing. I just did not want to use the words "premature ignition" because they sound too much like another phrase.:whistle: :woohoo: :blush: "detonation" is when the fuel no longer has the engineered burn qualities and actually "explodes"

:laugh:

I think we should point out that the only desired ignition in the cylinder is the controlled burn from the spark and flame that expands from that.

By increasing the spark gap, we are just speeding it up slightly, in a controlled manner.

Auto-ignition/pre-ignition happens spontaneously and is uncontrolled and undesireable, and can lead to detonation. All bad.

From what I've read, preignition is much harder to detect, but can still cause major damage. Supposedly it results in a relatively small, clean hole in a piston crown.

Detonation, will make a hole that looks like it was hammered into the piston with fractures etc..

loudhvx wrote: :laugh:

I think we should point out that the only desired ignition in the cylinder is the controlled burn from the spark and flame that expands from that.

By increasing the spark gap, we are just speeding it up slightly, in a controlled manner.

That's what I don't understand because I can not imagine why. If you look at the volume inside the cylinder compared to the size of the spark, it is many orders of magnitude larger. I can't get how changing the height of the spark could have any appreciable effect on how the burn radiates out from the point of ignition.

The reason this gets me is because I was a power supply designer. The flyback converter (which a car/bike coil actually is) is one of the oldest designs known. It would be very easy to increase both the voltage or energy at the plug by simply tweaking the coil (transformer) a little at the expense of a bigger coil. If there was any horsepower to be had that way, I am pretty sure the Japanese bike makers would be exploiting it, they are pretty slick at electronics. Given that everything has cost and tradeoff, I always assumed they increased the spark energy until there was no more gain to be had there and stopped. There is no question a weak spark can cause loss of power, I have just not seen evidence that a "super" or "increased" spark increases power beyond what a proper running ignition delivers.

OK Than I will only say one thing. Dual Spark Plug Ignitions. Why?

otakar wrote: OK Than I will only say one thing. Dual Spark Plug Ignitions. Why?

I hated changing 8 plugs in my ford ranger for that reason.....

Well, lets take a 2-dimensional analogy.

Lets say that if the spark gap is .030". Then (just making up numbers) let's say 1 msec after the spark, the flame front is 1 inch wide. Well then wouldn't it follow that if the spark gap is .060", that 1 msec later the flamefront would be near 2 inches wide?

Even if it's not a 1 to 1 ratio of spark gap to flame front size, it would only make sense that the flame front would have to be increased by some amount.

The flame front spreads in all directions and spreads by coming into contact with raw mixture.

Let's say every ignited molecule can ignite 3 other molecules. In 1 generation, starting with one molecule, there are 3 more ignited molecules. In 2 generations you would have 9 ignited molecules.

But if you start with two ignited molecules, then in 1 generation you have 6 more ignited molecules. Then in 2 generations you have 18 ignited molecules.

With each generation, the number of molecules burned is double. Idealized, this means the burn time would be cut in half. Obviously this is not exactly how it works since as more and more molecules are burned, the number of contacts get reduced.

At least that's my understanding of it. It's not like I did any real testing in a lab or anything.

otakar wrote: OK Than I will only say one thing. Dual Spark Plug Ignitions. Why?

Because if one is good, then two has to be twice as good.

bountyhunter wrote:

otakar wrote: OK Than I will only say one thing. Dual Spark Plug Ignitions. Why?

Because if one is good, then two has to be twice as good.

why dont they use larger gaps and coils instead of adding a spark plug ?

i think it has to do with chamber shape, and size. the larger the chamber (think larger displacement vs smaller) the farther the flame has to travel. 2 plugs placed father apart, cuts the distance the fame must travel in half.
it seems to me that i recall reading that higher compression ratio had something to do with requiring higher spark as well. something about too much compression blowing out the flame ?
there must be something to that since all the drag racers run more powerful coils.

if u look closely at a newish spark plug from a motor that has had detonation, u will see small silver specs on the insulator. I have seen this in my motor before installing a dyna2000,and coils.