The RX8 coils are the only [coil on plug] coils on the market
that [are designed to] fire 9000 times a minute.

The GM LS2 or LS3 or GM truck coils are only designed
to fire 3500 times a minute at the most.
Some are using them on the rotary and there is some
evidence they start having trouble around 6500 to 7000 RPM.

The reason for this  is the four stroke piston engine
fires the plug every other revolution. So 7500
RPM in a Corvette engine the plugs are only firing
3550 times a minute. A rotary fires the plug every
revolution. One reason they get so much power
for the small size of the engine.

I therefore conclude the RX8 coils are our best bet
long term. Mazda had trouble with the early versions.
Some early coils over heated and died killing the engine by
washing off the apex seal oil with raw unburnt fuel.
Poor Mazda had to increase the RX8 engine warranty to
100,000 miles or eight years.

I must say I am not surprised because Mazda was out
there on the bleeding edge with a 9000 RPM
red line and a rotary to boot. Law of unintended
consequences.

Mazda finally identified the problem and improved
the coil (we think) about 2006 to 2007.

Here is a heat sink that should add a bit of long term
reliability.

If you  are running a 2.85:1 gear box I recommend RX8 coils.

Paul Lamar

    Wait a minute, 9000 RPM with an 8 cylinder engine is 72,000 sparks
in two
    revolutions. That is 36,000 sparks by the old coils per minute. One
    coil per
    plug with the Pertronix should work.

    Dale Davies

Really? Back in those days we rarely saw 8500 RPM. After
2 hours the Chevy engine was junk with hundreds of cracks
every where including the block.
I was with the Jerry Titus Pontiac TransAm team and we ran Chevies.
Before that I was with Chaparral. The max RPM and life of the
Chevy V8 engine was the same. To get it to go 24 hours
we had to back it off to 7500 RPM and then it was junk
if it even made 24 hours.

Yes I can see how shortening the stroke
will raise the max RPM. The 2.4 L Form 1 V8 with about a 1.5 inch
stroke are turning up to 19,000 RPM. The bore is limited to
3.85" so that puts a lower limit on the stroke.  Each cyl is limited
to 18.3 cubic inches. The area of the bore is 11.64 square inches
so the stroke is 1.57 inches.

But this does bring up a good point. As I recall the distributer
had eight wires for eight plugs and the distributor shaft  ran at
half crank
speed or 4250 RPM times 8 or 34000 sparks per minute. That is 566
sparks per
second or one spark every .00176 seconds. That is 1.76 millisecond.
http://auto.howstuffworks.com/ignition-system4.htm

That is not much dwell time at all. An amazing coil. Perhaps they
were CD systems as I did not pay too much attention to type of
ignitions on
the engines. They came in a crate from GM or the contract engine
builder.
The spark must have been falling off with the points floating.

Now if they were two level distributors with two sets of points then
each set of points had only 4 plugs to fire so the dwell time
would double to 3.53 milliseconds. A more reasonable number.
About what the LS2 is today.

Check my arithmetic. I have been known to make mistakes.

Paul Lamar

Dale,, The petronix 60,000 volt "flamethrower" part number 60130  which
  comes with a heat sink is  sold through O-Rileys auto parts looks good
to me for inductive ignition. The second strike CD ignition add on also
uses this coil for the CD spark. With the capability of 60 sparks per
shaft revolution it seems like putting out four sparks for a multi
strike
ignition leaves 8/9 of the revolution idle for cooling.There are also
two lower voltage output models.

george grimes7

"With the capability of 60 sparks per shaft revolution"

At what RPM?

Paul Lamar

Paul,   As I recall the upper limit is 9000  RPM in the catalog on their
web page. As regarding dual point distributors. I have had a bunch
of them. I had  a 1933 steel bodied street rod. First engine was a
325 ci in "super red ram" hemi, then a 354, a 392, and a 440 six
pack. All but the 440 were hemi head types. The dual points were
both grounding the same coil lead. One coil output to the center if
the distributor with 8 leads from the distributor cap to the plugs.
The best shift point was around 6100 RPM and the rev limiter on the
six-pack was set to 10,000 RPM. I had valve train including a rev
kit on the lifters and lash springs on the rocker arms which were
advertised for 13,000 RPM. I broke a transmission input shaft (my
fault) and the blower turned it to 14,300 on the data sheet before
the ignition had time to react. This engine had a vertex mag with
one point set. There was no damage detected and it was run another 3
years on the same bearings and crank. Two sets of aluminum rods were
changed out but everything else was still in the car when it was
sold.  We sold "Nicky" chevrolet crate engines (427 cu in L88) as
replacements for 396 and 454 engines which the locals were having
trouble with the #3 main bearing web in the block and assorted breakage.

   I  don't remember any failures or operating problems with these
ignitions and don't recall hearing of complaints from the guys
running 301 duntov,and 327 chevy or 289 ford engines which had much
higher RPM operation than my Dodge engines. Intuitively it would
seem that a coil on plug system should be a much lower duty cycle.
That makes me wonder what is causing the problems. The mechanical
points back in the day could operate 4 times per revolution  at a
minium of 5000 RPM on a passenger car. A transistor and most solid
state devices can operate in the Mhz range yet all this high tech
stuff seems less capable  than a car built  50 years ago.

   The first thing I remember changing was the spark plug gap
increasing from .035 to .060 so that might be a factor. There are surely
changes in the core laminations and coil turns ratio of the coil
which is basically a transformer to change to the "high energy"
classification.There hasn't been much discussion about hall effect
sensors/reluctors not being up to the task which would seem to indicate
a reliable signal is being generated.The common thread to the
remaining components is that they are potted into a vibration proof
moisture resistant monolithic block. Some of the components are
apparently convienantly packaged with a heat source(inside the coil)
ensuring  they will have difficulty  conducting heat away  during operation.

   It would seem that a circuit board containing only components
necessary for operation whithout thermal overload checks,  test
points, diagnostic outputs and 1000 lines of assembly language
 would be a better way to go for a fixed advance aircraft
installation. The board would be waterproffed with a minimal coating
of clear epoxy for moisture protection and mounted in a resonable
sized enclosure.  A completely independent system for the railing
plugs should suffice for redundancy. A double pole double throw
toggle switch to change from leading to trailing plugs operation
would be the limit of non necessary parts.  The ignition coil should
be one containing only the core and windings of the turn ratio
necessary for 50,000 output voltage. This aparently would be from an
engine which had a distributor ignition. I don't know how much
supurfulous stuff is in the current circuitry however what seems
necessary would be a switched 12v supply, a resistor to reduce some
of it to 5v, 2 hall effect sensors with capacitors and diodes to
trigger the 2  transistors. The transistors and a large capacitor to
operate each coil.

   When I see a circuit board with processors, prom chips , lots
of voltage regulators AD converters,  and tiny resistors and capacitors
I wonder about the flight safety of these things when lightening  and
static electricity come into play. I can understand the complexity when
we are operating sequential fuel injection and mixture control but I
don't buy into the idea that lightning would take out everything so
it doesn't make any difference if the ignition is vulnerable. If the
ignition is the failure point that seems to be something that can be
avoided or reduced by using a minimum of robust components.

george grimes

Those old coils where really big and oil cooled. That may have had
something to do with it.

Paul Lamar

All this miniaturization is great stuff in  some applications. For an example
though lets look at recip. engines for a minute. Your basic small block
engines, be it Ford, GM or Chrysler can produce 350HP reliably. They can be
made to produce considerably more. Now when you do that the engine life is
reduced substantially.

Industrial engines are designed to produce their maximum power for months at a
time with engine life between overhauls in years. They get away with it by
having big, heavy cast iron cylinder blocks. Lots of iron for stability.

When it comes to machining equipment, there is no replacement for lots of cast
iron for the same reason.

Now back to the coils; the old inductive coils were large by todays standards.
But they lived for years relatively trouble free. They would do a superb job
as coil on plug with a CDI box driving them.

A V8 auto engine on the highway at legal speed used to run about 2,000 RPM. That
is 8,000 sparks per minute. A [one rotor] rotary running at 7500 RPM with coil on plug would be 7500 sparks per minute. At cruise that should be 6,000 sparks per minute. That should provide a reliable ignition on the rotary engines. The
Pertronix CDI Second strike can be triggered with a hall effect or LED trigger
system which is extremely reliable compared to points. The trigger system has
minimal electrical load on it. Engine bay heat is the enemy there. It is the
secondary side that needs to be robust in design.

Dale Davies

The one rotor fires once per revolution so a two rotor fires
twice per revolution. 7500 RPM in a two rotor is 15,000 Sparks
Per Minute. 7500 SPM for each rotor.

"A V8 auto engine on the highway at legal speed used to run about 2,000 RPM."
Each cylinder fires 1000 SPM. Every other revolution for four
cycle engines.  8 cylinders = 8000 SPM total. One coil.

At 7500 RPM 3750 SPM per cylinder or 30,000 SPM total for 8 cylinders.
That is 500 sparks per second. .002 seconds or two milliseconds (2msec)
from zero current to near max current.

One heck of a coil!!!

Consider R = 2 in the following equations. That is the aprox DC resistance
of the primary of the coil yielding a steady state current of aprox.  6 amps.
The old coils would get hot enough to burn your fingers with the points
closed and the engine not running with the key on. Power = E X I
or 72 watts.

Paul Lamar

http://en.allexperts.com/q/Physics-1358/Inductor-Charging.htm
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When a voltage, E, is applied (for instance by closing a switch) across a series R and L, the current will increase to the value
Ifinal = E/R. (You call this charging the inductor - that is valid but I prefer to think in terms of the current increasing. If it helps you understand to call it charge, that's fine.)

If there were no L in the circuit, it would reach this value instantaneously. But it doesn't reach this value instantly when the L is there. (L is assumed to be pure inductance - no resistance in the component.) The L fights the change in current. But when the fight is over, the equilibrium current is E/R. The equation that gives the response versus time is

E = I*R + L*di/dt

[E is not the battery voltage. It is the voltage across the coil
as a function of time.]

This is a differential equation that has the solution

I = (1-e^(-t/(L/R)))*E/R

L/R is called the time constant of the circuit: TL or Tau sub L. At time t = L/R, this reduces to (1-1/e)*E/R. So in one time constant, the current increases to about 63% of the final value. The current, over time, asymptotically approaches the final value. When it finally reaches final value, the inductor has the maximum energy it can have with the resistor R and voltage E in the circuit.

So, with Tau sub L = L/R, the time to reach 63% of the final value decreases with increasing R. This is true if a voltage is applied from a starting condition with no current in the circuit. If the voltage has been applied for some time, and then the voltage is suddenly reduced to zero, the current will continue to flow because of the energy stored in the inductor. (I don't mean the voltage source is replaced by an open but by a short.) The decreasing current will follow the same characteristics. In one time constant (Tau sub L = L/R), the current will decrease 63% of the way from the original I = E/R equilibrium level to zero.

Why does an inductor 'discharge' faster through a high resistance? Because the resistor decreases the amount of energy the inductor can store. Because the current doesn't get as high as it would with a lower resistance. The 'charging' of the L with energy is the mirror image of the 'discharge'.

An example about the time constant: if R = 2 kOhms and L = 4 henrys, the time constant L/R = 2 msec.

I hope this helps,
Steve
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