Duke, what's your take on this spark equality.

[Domenic T.]

I was reading a recent post where you were addressing point ignition and electronic ignition and it made me think of the advertisements in the 60's where they claimed more HP with a hotter, longer spark.
Question being is that you were, or still are involved in aviation. The engines have 2 ignition systems for each cylinder, 2 firing spark plugs per cylinder. During a ignition tet before flight each is operated separately to verify it working. The power loss is estimated at about 5 to 7 percent when only using one system. This is on a common flat opposed engine usually there'd at 1700 RPM. The RPM's drop about 125 when on one spark source. Remembering that that is only a test RPM. The normal running RPM is about 2750 and up to about 3500 on specialmapplications.
Here is the question, not a debate but just a question. I would think that a longer, hotter spark would add to the HP as they advertised when the electronic ignition first came out. You mentioned there wasn't much of, or no difference on a point system vs electronic system, if I remember your post correctly.

What's your take on the power gain with double the spark as in the proven aircraft tests? Granted the 2 systems are there for safety but they are both needed for performance figures.

Respectfully, DOM

[Duke W.]

Re: Duke, what's your take on this spark equality.

Two plugs per cylinder reduce the advance requirement compared to one because two combustion kernels are started. If you were to disable one set of plugs on any twin plug system, then advance the timing on the remaining single plug to achieve optimum output, it would likely be very close to twin plugs with optimized timing.

Twin plugs might have a bit of an advantage, depending on combustion chamber design, because combustion is complete in fewer crank degrees, which comes closer to the ideal of combustion at constant volume.

You might recall from my San Diego presentation that with typical combustion chamber designs, combustion is complete about the same number of degrees ATC as optimum advance is BTC.

I recall reading back in the early seventies when Ferrari seemed to have a new F1 engine virtually every race that one had three plugs per cylinder. The writer astutely remarked that if it took three plugs to light the fire, there must be something wrong with the combustion chamber design.

Multiplug designs are few today because four-valve heads allow a single plug to be placed near the geometric center of the combustion chamber, which is ideal.

Duke

[Domenic T.]

Re: Duke, what's your take on this spark equality.

Duke,
Makes sence to me. I lost my post with more about this but can't reach it from this computer. I will post it in AM.

DOM

[William F.]

Re: Duke, what's your take on this spark equality.

Duke,
All modern Chrysler corp hemi engines have 2 spark plugs per cylinder.