Gentlemen,
This weekend I took the $75 plunge and replaced the coil on my E-Type. I
went to a typical north American “Speed Shop” that sells stuff for
Chev/Ford etc., and picked up a coil designed to be used in a “Mallory”
electronic ignition system. The size is identical and except for the
colour, (bright red), it fits just perfectly. The hookups are the same.
On firing up the car, it starts much more readily, in 3-4 revolutions from
cold and one rev from hot… On the highway, the engine. The engine seems
to pull more strongly and the exhaust note I can only describe as
“Cleaner”. At idle, the engine is also much more stable. Regarding the
idle quality, I did reset my Fuel Temp Compensators so that they are
beginning to open just above room Temperature (probably about 30 deg.
Cent.), and haven’t checked the mixture, but I’m sure the coil is helping.
I now need to see about resetting the idle mixture which I could not do
before - I could not get the mixture Lean enough. Hopefully, with the
compensators readjusted, I will be more successfull.
As the new coil is defined as a “High Output” unit, I also plan to start
experimenting with the Spark Plug gaps. The originals are at .025" and
will be reset at .040". I will report back to the list with the results of
this change. Unfortunately I am writing this on my way to Japan (business)
and so will not be able to get to the Jag until early June.
I’m very interested in your research about varying the gap inthe spark plugs.
I don’t know a thing about trying that, but a racing friend used to vary them
within a set of 8 in his car depending on how far and how different the
mixture went through the intake manifold. This was in the days of one carb for
all 8 cylinders.
LLoyd - now in the new and improved 2+2 size
(what have I DONE!! )
Regarding iramphal - Lloyd - Ignition Coil and plug gaps
Years ago, I know here we go again - in the old days— when the plugs fouled
out or you really flooded the engine, one of the tricks to get the plugs to
fire was to pull the coil wire out part way from the distributor cap. What
this did was cause the coil to put out a higher voltage (50000 volts) than the
normal 20,000 volts required to jump the .028 plug gap and the rotor-to-cap
gap at each tower inside the distributor cap. This usually was enough of an
increase to fire even the most crapped-up spark plug. After doing this a
number of times we thought “Hey why not just make a fixed additional jumper-
gap device to do this all the time” . Just think, no more fouled plugs, the
engine runs smoother and stronger too. Have you ever been to the county fair
where there’s a guy with a microphone, his hood open on his car, hustling a
device called a “Super - Spark Intensifier " or other name. Same thing as
pulling your coil wire part way out only it costs $49.95. The only problems
that may crop up sooner than normal are: your standard coil will break down or
over heat , the distributor contacts may burn away sooner or moisture will
allow the cap to " carbon-track” or jump spark to ground quicker, or the
points may “pit” quicker due to a change in the primary induced voltage from
the coil that a standard condensor can’t handle. Widening the plug gaps will
do the same thing to a standard ignition system. If you do open the gaps on
your system (high performance coil- standard everything else) keep close tabs
on the other components. The auto manufacturers caught on to this when they
brought out the high energy ignition systems in the early 70s . Emissions were
a problem that were controled alot easier when the plugs fired every time no
matter what. So better distributor caps and rotors, thick high-energy plug
wire sets, resistor spark plugs (.040 gap) , high voltage coils, and
transistorized primary ignition assemblies did away with the points and
condensor. But even the early systems had overheating problems till all the
bugs were worked out. Especially the Lucas Opus on the V-12 E-types.
Enough history for today. Oh yes, play with the timing if you change the plug
gap, a little more advance possibly, but watch for “pinking” on acceleration
and keep tabs on the coolant temp. Regards Steve Rauch
At 21:19 2/06/98 EDT, Pleiku604@aol.com wrote:
Regarding iramphal - Lloyd - Ignition Coil and plug gaps
Years ago, I know here we go again - in the old days— when the plugs fouled
out or you really flooded the engine, one of the tricks to get the plugs to
fire was to pull the coil wire out part way from the distributor cap. What
this did was cause the coil to put out a higher voltage (50000 volts)
Actually, the reason this strick works is not the higher voltage, but the
faster rise-time at the plugs, more like a CDI rise time.
Widening the plug gaps will
do the same thing to a standard ignition system.
No, actually it does the opposite, it slows the rise time at the plugs and
makes the plugs more prone to fouling, but with more energy in the spark
when it does happen, it is better at igniting a lean mixture.
On the subject of the spark enhancers, some of the double-ended coils for
distributor-less systems (mainly Japanese) actually have a series spark gap
built into the coil secondary to serve the same purpose.
regards,
Mike Morrin
Well, this entry has generated lots of discussion! Now that I’ve conducted
this mod to the plug gaps, can anyone tell me what if any influence it will
have on the reliability of the standard OPUS system? I assumed that the
interaction of the OPUS stopped at its termination at the coil. After all,
isn’t it true that the OPUS just sends a continuous oscillating signal to
the coil causing it to fire continuously? There is no timed spark out of
the coil, only a steady stream of sparks sent to each plug as the rotor in
the distributor sweeps past the terminal posts on the distributor cap.
Correct me please if I’m barking up the wrong tree.
Ian
At 13:18 3/06/98 -0400, iramphal@dehavilland.ca wrote:
Well, this entry has generated lots of discussion! Now that I’ve conducted
this mod to the plug gaps, can anyone tell me what if any influence it will
have on the reliability of the standard OPUS system? I assumed that the
interaction of the OPUS stopped at its termination at the coil.
After all,
isn’t it true that the OPUS just sends a continuous oscillating signal to
the coil causing it to fire continuously?
NO!!!
There is no timed spark out of
the coil, only a steady stream of sparks sent to each plug as the rotor in
the distributor sweeps past the terminal posts on the distributor cap.
Correct me please if I’m barking up the wrong tree.
The OPUS system fires a timed spark just like every other (non CDI) system.
The transistor switches on, current flows through the coil primary, and at
the correct firing angle, the transistor turns off, causing the magnetic
field to collapse and the coil to produce a spark.
I have heard of OPUS amplifiers which produced continuous sparks, but these
were definitely faulty (or had incorrect wiring to the trigger unit).
What is unusual about the OPUS is the way that the timing position is
established, using a high frequency (600kHz) oscillator and a balanced
transformer which is momentarily unbalanced by the 12 ferrite rods mounted
in the distributor rotor.
When introduced it was also novel (but its reason for being used on the
V12) in that it had very long dwell angle, allowing the coil maximum time
to build flux at high RPM.
Note that there were 3 different versions of the OPUS mark 2 amplifier,
each one a little more rugged, the second type (C39955 from engine 7S16210)
was able to drive a high energy coil, and the third type (introduced in
1980) was remote mounted and had different connectors.
I don’t know what the actual coil ratings are for each variant, but I would
assume that even if you do cook the output transistor, a more modern
transistor could be substituted easily.
good luck,
Mike Morrin
'73 2+2
'75 XJ-S
Mike - regarding plug gap
The reason I know there’s a voltage increase is, when we were using an
ocilloscope to check out the ignition systems, a larger secondary voltage
spike “rise” showed on the screen other than a slight shift in condensor bleed
down time. Comparing the voltage at plug fire time, with the gap set at
standard .028 and then opening the gap to .040, the voltage required to jump a
larger gap is higher, which is what the scope calabration lines verified.
Ian - Regarding Lucas Opus
The amplifier unit recieves a magnetically induced trigger signal from the
distributor. If you remove the cap an take a look under the rotor, there is a
trigger wheel with 12 small ferrite iron bars evenly spaced in the plastic.
These bars rotate past a small pickup-unit (a small coil with a center core) .
Each time these two items intersect a signal is sent to the amplifier unit ,
which intensifies it and sends an on-off switching action to the coil. 12
volts are at the small +terminal on the coil ,which is sometimes conected in a
series with a resistor unit , when you turn on the ignition. The grounded -
small terminal is connected to the amplifier unit. Each time the primary
windings of the coil are energized with 12 volts (larger windings 100 wraps of
wire, it creates a magnetic field around the core) . When the amplifier
recieves the signal to cut off the power to the coil primary, the magnetic
field colapses and a voltage is induced in the secondary coil windings (6000
wraps of finer wire around the primary windings ). The coil is a transformer
that converts one voltage to another (12 to 50,000volts). The amount of
voltage needed is decided by the gap it must jump (wider the gap -higher the
voltage) until the coil will not be able to develop enough “spark voltage” to
jump the too large gap, or there is an alternate route the spark will take.
This happens if the gap or insulation value on another component is a lesser
value (cap, rotor, plug wires, top of the coil to the case, ect). If
everything works the way it should, the spark is then fed to the center
terminal of the distributor cap, center of the rotor, and is timed to deliver
the spark when the rotor tip and each cylinder plug wire tower contacts are in
close index. The spark jumps that gap travels down that plug wire to the spark
plug where it jumps the plug gap you have “set”. Heat is the number one
nemesis of a transistorized system. When too much heat builds inside the
amplifier unit the circuits shut down and you loose spark. The early Jaguar
V-12 s with the amplifiers located in the engine valley, between the cylinder
heads, under the A/C compressor were notorious for “No spark when hot” . This
was solved by a service campaign of moving the amplifier to the radiator
header panel away from the intense heat on the engine. I’ve babbled enough,
hope I answered your question.
Regards - Steve Rauch