how waveforms affect performance

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Joined: Wed Sep 15, 2004 1:13 am

how waveforms affect performance

Post by sprince » Wed Sep 15, 2004 1:25 am

I just purchased a Pico automotive analyzer to view the secondary waveforms of different ignition systems. For the primary waveform, I've been using a Fluke handheld oscope, but nothing for the secondary.

My question is: when viewing the secondary waveforms from different ignition systems, there seems to be very little difference (I have the waves saved if you would like to see them) in the traces, but a HUGE difference in engine performance when measured on a dyno.

Although the timing tables are different for the different ignition systems, they are within 5 degrees of each other, yet the horsepower numbers vary by 15%!!

Any ideas why?

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Post by Autonerdz » Wed Sep 15, 2004 4:00 pm

Hi Sprince,

As you have already discovered, PicoScope can show intense detail on secondary ignition. To try to address your question...

When it comes to ignition, timing is a huge part if it. The timing curve should optimize the burn over the RPM and load range for a particular engine. The goal of the ignition is to provide enough energy to keep the spark lit as long as there is fuel to be burned.

While different ignition systems have different ways of controlling the timing like mechanical or computer control etc, when it comes to the actual spark production, they all have to do the same thing. The primary drive must build a field and then collapse it effectively. They all are working with the same physics and the result is similar. Whether it be COP, DIS, or distributor the goal is the same. The secondary waveform itself will reflect the similarity, however there are distinct differences between a DIS (one coil for each two cylinders) and a distributor system. Most notably is the fact that, on a DIS, one plug fires positively and the other negatively.

Some systems may show more energy oscillations after the spark line than others, but differences in the spark line behavior speak more to what is going on in the combustion chamber than the ignition system. Two engines running well will have very similar secondary behavior.
Tom Roberts
(The Picotologist)

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