Thanks for the videos MPA!! Some good info there

Thank you.

I have a different view of what happens there.

The points open and the field collapses. As the points open, the coil current can take a path through the condenser rather than jump the opening gap of the points therefore minimizing sparking and eroding of the points.

Also since the the condenser is now in series with the coil primary, it is a series resonant circuit. That initial collapsing field starts a decaying oscillation of that resonant circuit. That induces an AC current which produces output on the high voltage secondary with each swing of the primary current.

All that happens in a time period determined by the value of the condenser and inductance of the coil and in much less time than a fraction of a revolution of even high speed operation of the engine. Engine rpm has no effect on the length or strength of the decaying oscillation.

I would question the "using premium fuel which burns a little longer/slower".

Many people screw this up.

In most of the U.S., regular gas has an octane rating of 87, midgrade gas is 89, and premium is 91 or 92. (Octane ratings are lower in the mountain west due to the effects of thin air on internal combustion.) Contrary to widespread belief, the octane rating doesn't indicate how much power the fuel delivers; all grades of gasoline contain roughly the same amount of heat energy. Rather, a higher octane rating means the fuel is less likely to cause your engine to knock or ping. Knock, also known as detonation, occurs when part of the fuel-air mixture in one or more of your car's cylinders ignites spontaneously due to compression, independent of the combustion initiated by the spark plug. (The ideal gas law tells us that a gas heats up when compressed.) Instead of a controlled burn, you get what amounts to an explosion — not a good thing for your engine. To avoid this, high-octane gas is formulated to burn slower than regular, making it less likely to ignite without benefit of spark.

is formulated to burn slower than regular

We will have to differ on that one.
Higher octane rating means higher flash point, nothing about "slower burn".

We will have to differ on that one

.

I would agree not all premium blends apply.

BUT When you blend alkylate and or ethonal or even Techroline to raise octane into the fuel, it does have a higher flash point which "can" slow burn rate down, it is said to burn more completely leaving less carbon. Sunoco's race fuel site saying it's not true for racing gas but has some merit for pump gas.

It really depends on the blend. Different fuel blends burn at different rates under the same temperatures and pressures. Absolute fact.

So I will also agree with you for the most part, but different blends can reduce the burn rate.

Websites like this one disagree, but they are speaking about E85 ethanol blend.

http://hioctaneracing.com/blog/2011...t-e85-fuel.html

Having a higher octane rating, slows down the burn rate of the combustion cycle. This means that it is possible to increase the boost level, compression ratio, and/or timing advance and return the mixture to a burn rate similar to that of gasoline, having a comparable level of ’safety’ in the cylinder, a similar mixture volatility, but albeit at a much higher power level.

I honestly think their statements confuses flash point and burn rate.

I would say that atomization of the fuel in the fuel/air mixture has a much greater effect on burn rate than octane rating.

Since you bring up ethanol - - the 85/15 E85 has 28% less energy per gallon than 10/90 gasoline.

So if you're paying more than 72¢ on the dollar for E85 compared to gasoline - - you're being ripped off.

I would say that atomization of the fuel in the fuel/air mixture has a much greater effect on burn rate than octane rating.

Agreed.

on our engines people shoot for 12.5 to 13/1 as a center. Most are tuned pretty stable at 6000-7000rpm at that

the 85

LS7 loves E85 not inducted. People can raise compression really high. These engines are weak to detonation due to a thin ring land on the pistons.

I have a different view of what happens there.

The points open and the field collapses. As the points open, the coil current can take a path through the condenser rather than jump the opening gap of the points therefore minimizing sparking and eroding of the points.
Also since the the condenser is now in series with the coil primary, it is a series resonant circuit. That initial collapsing field starts a decaying oscillation of that resonant circuit. The represent an AC current which produces a voltage on the high voltage secondary with each swing of the primary current.
All that happens in a time period determined by the value of the condenser and inductance of the coil and in much less time than a fraction of a revolution of even high speed operation of the engine.

Ok that's the same view to this point Ive covered

But this bit

Engine rpm has no effect on the length or strength of the decaying oscillation.

Frequency wont change, amplitude or strength will
It has to with demand which is greatest at starting.

Ill be covering this in the vidoes

Well . . . now we have another previously unmentioned factor.

I agree that if the system voltage is depressed (the starter is turning over the motor) the strength of the spark will be less.

There's that too, but most have a ballast bypass during cranking.
The starting issue particularly cold starting is the demand on the ignition due to spark resistance.
Being spark resistance at the plug gap is determined by density.

The coil capacity remains the same but the firing voltage varies with spark resistance and any change in voltage be it the initial spark line, the spark timeline and the thereafter will be seen on the scope pattern (as change in amplitude). And primary being reflected in the secondary pattern.

As it takes more to get it started any deficiency in voltage or rate of change available will mean less reserve voltage available from the coil so poor condenser or coil winding or insulation will cause problems at starting, once you get the engine running it draws less.

Not the same as high RPM where lack of dwell time becomes the issue as RPM increases and so we get another deficiency at high RPM too.
All the reasons why we don't use them anymore.

You're starting to talk a lot of lesser variables. I question how much they really affect things.

Back in the day, we used a clamp on probe on the #1 spark plug lead to feed the scope. That was an inductive pickup. An inductive pickup depends on current in the ignition lead, not voltage. The current is driven by a high voltage from the coil against a resistance. Before long all plugs had resistors in them to minimize Radio Frequency Interference. I suspect that the resistance in the plugs also allowed a more consistent spark. So I'm concluding that "spark resistance" didn't have much to do with things.

Just how much dwell time had to do with spark depends on a number of things and the end result can be best seen on a scope as you rev the engine. (do the points close before the ringing from the previous opening finishes ?)

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IT's all pointless....hehehehe

I dream of a better world, A world where a chicken's crossing a road IS NOT questioned

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