Craig:

Please allow me to respond in text. There seem to be some misunderstandings.

... don't diminish the effects of a good ignition system. Poor plugs, bad wires,?worn out?mag (even hotter spark) all can make a significant affect for the same reason the RPM drops on one mag vs both.

Your comments are correct except for the reason the rpm drops on one mag. EGT rises on one mag because the total burn time is almost half as much as with two plugs. The rpm drops because the thetaPP becomes excessive.

If the flame is lit but the flame kernel is "poor" the cylinder will make power but not as much as if the flame kernel is "good".

This is dependent in large part on the mixture in the local area, not the intensity of the spark. Spark intensity can play a minor role, but the fire either starts or it doesn't. That seems to be more mixture-dependent in the local area of the electrode than anything else. Spark intensity does play a role as you suggest, but not as major as we once thought.

The idea is to have as fast of combustion as possible without it being an explosion (non controlled combustion).

No, the speed of the flame front is determined by the bulk gas temperature and the internal cylinder pressure. We do not want it as fast as it can be.

With 2 flame fronts (two spark plugs per cylinder) the combustion time is greatly reduced and therefore power is increased and BSFC is reduced (fuel economy is improved).

No, power is not increased as a result of two flame fronts. The total burn time is shorter, yes, but that is calculated for in the timing choice. It is quite possible to go to one mag and INCREASE the power output. If you takeoff on one mag in almost all of these GA engines, power output will be higher because the thetaPP will move away from TDC closer to 16? ATDC where power is at max from mechanical advantage of the crank. Frankly BSFC does not come into play here, and that's a whole 'nuther discussion I don't want to get into in this post.

Particularly on our big bore aircraft engines. Just changing your fuel from 100 octane to 130 octane will reduce power and fuel economy for two reasons.

This is not correct. The latency period of 130 is longer than that of 100LL. It may produce more power on takeoff but less in cruise than 100LL. That depends on the timing and power setting chosen.

1. The 130 octane fuel has less BTU's per gallon.

I don't think that is correct. If it is, it's not an operational difference.

2. The 130 octane fuel burns slower.

No, it does not burn slower. It has a longer latency period, but once it gets started, the flame front speed is the same. The latency period is that number of microseconds that exist between the spark and the organization of the flame front. It is longer in higher octane fuels which make the theatPP later in the down-stroke. That can result in higher or lower power, depending on many factors.

Some of this loss came be regained by advancing the ignition timing when running higher octane fuel.

This is true to a point. What you are doing by advancing the timing is trying to offset the longer latency period of the higher octane fuel. This may or may not be optimal. Once the timing is advanced beyond the point where the thetaPP is closer to TDC than 16 degrees, the power output will go down while internal cylinder pressures and CHTs go up.

It's not as simple as we thought it was when we were screwing around with the timing on our 57 Chevys! <g>

Walter