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Why
A
urelia’s convert to digital electronic ignition......
About advantages or disadvantages of analogue, digital electronic IC (inductive charge) or CD (capacitive discharge) versus conventional points
ignition systems applied in a classic car like my November ‘56 light chalky blue telaio #3900 Lancia Aurelia B-20. Basic functioning of different
charge build up systems is discussed because when asked how it worked I found about nobody able explaining it properly.
Last addition made December 2010 by Francosporto™ (LCN#C0897) himself, the Hague, NL
Conventional ignition systems all have some high tension coil in a magnetic field being switched off resulting in infinitely
increasing voltage in order to maintain its existing (Henry‟s Law) magnetic field ending up with a spark discharge if we are lucky.
Such circuit interruption can be made mechanically by contact breaker points or electronically by semiconductors like
transistors or thyristors.
So basically ignition sparks originate
from inductive charge or capacitive
discharge build up.
Primary system energy supply mostly
comes from a 6V or later on from a 12V
battery, but in the early motoring days
charging was supplied by rotating the
coil through a strong permanent
magnet‟s fixed field. It was called
“Magneto ignition” and was always
triggered by adjustable (right) contact
breaker points.
Advancing the ignition timing compensating the combustion process delay at low rpm can be made mechanically by vacuum moving
the ground plate or by centrifugal weights and springs moving the multi cam (below right) or digitally by electronic circuitry.
For multi cylinder engines actually each cylinder needed its own
(below 3 cylinder DKW 2-stroke car) ignition system or was served
by one such system connected through a distributor (left
Francosporto‟s 3C B-20) to the correct sparkplugs‟ high tension lead.
The Magneti Marelli
B-20 distributor cap
was quite resistant to
drip water already,
but frequently some
part of the high
tension voltage got
lost leaking to earth
too early because of
water, fuel mixture,
oil or carbon deposits
condensate on parts
insulated well known.
For all conventional
interruptive HT coil
systems the spark‟s
quality and timing
consistency was very
much depending on
the wear and tear of
the contact breaker
points as well as its
lifting multi cam.
A capacitor was also necessary reducing
contact points burning due to heavy
amperage to be switched off. This is
definitely also the difficult part for all
electronically
interrupted
ignition
coil
systems all the same to whatever detecting
device is used acknowledging although
transistors being rather sensitive for some
250V bursts in its primary coil circuit.
Thyristors handle these inductive peaks
much better, cheaper and reliable as well. At
Kröber GmbH they already knew this in the
sixties.
Correct ignition timing by optical or magnetic detection is basically not different from the classic
precision part called the multi cam. (above with 3 cams or far above with six )
Different grade plugs at right came from the #3900‟s engine as purchased got quite fouled up.
The real difference for nowadays Capacitor Discharge Ignition systems is in the HT coil‟s power
supply. A primary coil in a conventional circuit with a 12V battery has a much higher total resistance
compared to a circuit consisting of a small 1:100 transformer supplied with 450V from a capacitor of
almost infinitely low internal resistance. On the contrary large 12V batteries have considerable internal
resistance compared to small 550V capacitors enabling almost infinitely high current supply for short output
signals building up extremely quick. Apart from so called dwell delay taken by a conventional primary coil
building up a magnetic field, another delay comes on top of that caused by awaiting the high tension build
up in the secondary HT coil following the interrupted absurd 6 to 12 ampere primary current supply.
The HT build up delay is also uncertain because only the resulting inductive spark discharge is ending the
build up process which is very much influenced by conditions around the sparkplug‟s electrodes like the
engines‟ operating temperature, the opening gap and the ionization possibilities of mixture molecules
between them. So that‟s why in the old days engines wouldn‟t start at low temperatures as enriched
mixture condensed on plugs or plugs fouled up because of coal and oil deposition on insulators
inhibiting any HT build up at all. Notice of these old (right) Aurelia plugs the middle one being of
a higher temperature grade with its central electrode more exposed into burning mixture.
On the contrary CDI systems can produce such short output signals resulting in short high current and very high voltage output
(V x A = Power) resulting in high energy sparks almost independent from any build up time, even enabling triple or double sparks
up to 3000 rpm easily at very low mean current consumption from the battery. All 1960‟s multi cylinder (below twin cylinder
rotary valve Suzuki RT65) 2-stroke motor cycle
racers were equipped with magneto ignition
preventing them most certainly from current
starvation caused by a flat battery feeding two
to six coil systems with at least 20A to 30A
from one small but heavy 12Ah racing battery.
(titanium ortho poly tetra fluoride battery gel
tablets were not yet invented)
.
Historically the design advanced in time by replacing the battery
less inductive ignition magneto‟s (left late 70‟s MV four with
magneto between exhausts) into alternator powered CDI ignition
systems (right Honda RC115 50cc twin) basically functioning not
different to whatever interruptive device is applied be it optical,
magnetically or mechanical …… The
dwell time needed for charge build
up was the reason why some early
2-stroke motorcycle GP racers only
could get enough reliable sparks at
the time with double contact
breakers running at half rpm or the
rotor having only half of the usual
six or eight cams but finally getting their plugs fouled anyhow
because those sparks often were of low energy and often
insufficient to sensitive 2-stroke combustion. The fabulous (right)
9 speed Honda twin shows its right HT coil in the right upper
corner triggered by four magnetic pickups on a right side at half
speed running auxiliary shaft partly hidden behind the multi plate
clutch. Old fashioned dwell time could easily be overlapping the HT
charge time at over 19.000rpm‟s causing lower energy sparks only
solved thanks to Nippon Denso CDI magneto‟s.
After crossing the finish line victoriously in the 90‟s Valentino Rossi (below left Honda NSR 500cc 2-stroke V4 #46) only could
stop somewhere along the track going crazy with his “tifosi” throwing his helmet and gloves into the crowd for some minutes,
and yet continue his celebrating lap by easily jumpstarting his cooled down 500cc four cylinder Honda stroker thanks to his
Kokusan Dengi CDI magneto‟s . . . .
Nine years later the same
Valentino Rossi (right #46) riding
Yamaha‟s 800cc YZR M1 4-stroke
four cylinder is leading two
Honda‟s and indirectly the MotoGP
battle developed into competition
between Yamaha‟s main sponsor Fiat against the other car manufacturer . . . . Honda
(compared to the comparatively small amount of money involved the “Torinesi” also
could have engaged the successful Audi Spider LM TDI‟s at Le Mans 24 hours with
for instance their secret all new Thesis Spider LM Multiair TDI Sperimentale.
Actually the so called CDI “magneto‟s” were flywheel alternator powered CDI
ignition systems and had nothing to do with magneto ignition found on a Manx Norton
or G50 Matchless single cylinder racer basically still being of inductive origin except
maybe for the primary energy being alternated by a magnetic field movement.
In the old days the glazed layer of
condensed racing oil covering the plugs‟
electrodes would be too much for
restarting these engines. Although rather
valuable flywheel alternated Thyristor
ignition systems were available from
Kröber GmbH the fabulous 105kg 125cc
nine speed V4 Yamaha 2-stroke factory
racers screamed along at 18.000rpm
depending (right) on twin magneto‟s for
their ignition system still frequently
suffering from ill misfiring on one or two
cylinders, similarly to Bill Ivy‟s amazing „68
2-stroke 350cc Jawa V4 (2x below)
depending on 4 separate CDI systems
challenging Giacomo Agostini‟s three
cylinder 350 MV to the limit until ... ... ... ...
For classic display racing Ferry Brouwer later on converted those
Yamaha‟s to digital CDI systems hidden into the genuine magneto‟s
housing still looking original and running without missing one spark
at much lower mean current consumption although on the contrary
the early 125 2-stroke MV single (below left) just used simple
flywheel alternated (early racing Magneto ??) contact points
triggered inductive ignition.
Even a 4-stroke GP racing car like the V8
Lancia D-50 (right) had 16 sparkplugs
changed for colder grade racing plugs
after warm up preventing them to burn
away under race conditions or foul up
immediately if being initially too cold.
Actually this was the reason for the
famous push starts at motorcycle GP‟s,
because the fresh cold grade racing plugs
only would function well under full race
conditions and riders had to care
maintaining their ideal plug operating
temperature by smart throttle control. So
when held up by slower riders a relatively
cooled down plug could foul up easily and
speeding up at overtaking them would not always burn plugs clean again. Restarts
were complicated if not impossible in case of a major race incident because always
new plugs had to be installed followed by another push start.
Back to Aurelia’s
At determining the best suitable ignition system for my #3900 Aurelia all
uncertainty‟s and disadvantages as discussed above as well as the kind of
triggering device are considered always maintaining our all important classic look.
Besides all this a principal advantageous accuracy level of triggering signals from a
crankshaft will be far better at increased (right) working diameter providing
higher tangential speed and consequently less advantageous will be any at half rpm
rotating camshaft derived triggering signal. Much larger circles are dividable
more accurately into equal intervals.
A small opto or magno rotor sized to function under an original crampy distributor
cap has to be manufactured at very high precision to get anywhere near flywheel
accuracy. So compared to any at half speed rotating device general signal
accuracy will be less and so you can figure out yourself why most today‟s modern
cars as well as all F1, DTM, Le Mans or WRC cars are triggered from the flywheel.
Even “classic” fly weight ignition advancement with also classic unreliable (right) springs is replaced by
programmed digital advance curves and fortunately related functions can be derived like start retard, rpm
limiting, fuel injection, distributor less ignition, electromagnetic or pneumatic valve actuation as well as
traction control, launch control and telemetric control.
For our classic car we would like to have all these advantages, but avoiding the
car is driving me instead of the other way around but anyhow not having these
gadgets makes driving our classic cars ultimately charming except for poorly
performing ignition only as long as all electronics can be kept out of sight.
Notice Aurelia‟s by nature having the most beautiful distributor cap in the entire
automotive industry (below) fitting neatly behind (right) the #3 carburettor and
one cannot think of but one single reason why classic car owners tend to install
such shiny red bulky heavily
chromed exchange distributors
in full sight on top of their all
original B-20 block. Oddly we
are spending fortunes on
original or original looking parts
but try saving some money on
proper ignition and in fact our
very characteristic distributor cap is valued only one third of for instance a
MSD system. There can‟t ever be any reason murdering your original look
unless you are going to burn nitro in your fuel, basta !
So my Aurelia B-20 needed an apparently uncommon 6 cylinder interval CDI
power unit triggered by a timing device of high accuracy but versatile enough
suiting my experimental 3C setup consequently having adjustable parameters
as much as possible later on resulting in most interesting reports on this
continuing site.
Unfortunately not cheap at all (right;
with
Principe
Tomasino
II
surrounded with nice goodies) yet
very suitable for the job are the
modular digital CDI systems from
MSD El Paso Texas USA. For sporty
street use my classic Aurelia B-20
needed nothing more than their
Series 6 system.
So the optimal choice means the
MSD 6-AL CDI “Ignition Control”
actually being a modern version of
the analogue 450V Kröber CDI HT
power supplying unit. The 6-AL unit
(right; far left to Tomasino) is
adjustable to 4, 6 or 8 cylinder
engines and can be triggered from
contact breaker points as well as
analogue or digital circuitry, but as
earlier discussed triggering from the
flywheel will be optimal.
Three magnets at 120° intervals (above left) mounted on the
flywheel passing along an opposed detection coil (above right)
mounted on a light alloy mounting plate (below left) fixed on the
light alloy flywheel cover. The gap in between can be adjusted by
screwing in or out the ½” sensor locking its locknut with some
locktite.
Since the “Programmable Timing Computer” (PTC) (above; right left
of Tomasino) allows digital timing adjustment the sensor coil‟s
mounting plate does not need to be adjustable as long as the
mounting plate is somewhere over one of the three magnets with
the #1 piston at the TDC mark. Our “PTC” supplies even three
different advance curves and enables easier engine starting by
retarding the ignition with some 20° and consequently the starter
motor needs less current from the battery. In the old days of
motoring ignition retarding was common practice with a “manet” on
the steering wheel preventing the engine to start reversed getting
ignited just before TDC. Quite some people got injured by a back
lashing hand crank.
Non magnetic detection devices triggered
from the flywheel quite close to the starter
motor are not considered because of
possible interference. Furthermore the
robust GM triggering device (right) does not
fit under our relatively small Magneti Marelli
distributor cap while compatible 6 cylinder rotors seem to be not available.
The flywheel got milled (some 5mm) from the back face reducing weight to 10kg and three light alloy
bolts (far above) carrying the magnets are screwed in. In this situation getting the bolts more flush into the flywheel they
remain to be screwed in 5mm more not to interfere with the inside of the (above left with trigger coil bracket) cover plate.
Special braided HT leads (far above; right of Tomasino) are always needed to deal with these high energy sparks and will be
normally connected together with a canister type MSD (far above; almost in front of Tomasino) high tension coil to the original
distributor cap. So we have to wait and see for the engine‟s first firings to learn about possible 45kV cross firing beneath the
distributor cap maybe needing gold plating the original slightly worn rotor contacts.
To be continued soon
…………………………
Then we will discuss installing and wiring the MSD hardware, hiding all components under the dash and finally the actual ignition
timing adjustment procedure. Maybe also some thoughts about current consumption of various systems in our Aurelia compared
to battery size and the B-20‟s somewhat undersized alternator capacity will also be brought to your attention.
Francosporto‟s Related Links :
Below but unfortunately some parts are still in dutch but digipics are great !
Home : http://www.lanciaaurelia3c.nl/index.html
Aurelia Mania: http://www.lanciaaurelia3c.nl/aurelia%20mania.htm
Classic thinking: http://www.lanciaaurelia3c.nl/classic denken.html
Why not 3C : http://www.lanciaaurelia3c.nl/toch%20maar%203c.html
Home : http://www.lanciaaurelia3c.nl/index.html
Martin Willems : http://www.martinwillems.nl/ or http://www.b20.nl/
DCNF40/Aurelia3C-manyfold at You Tube: http://www.youtube.com/watch?v=Db8lBtvNjMM&feature=channel_page
Vere Lancia Racing : http://www.lanciaracing.com
VCR engine video : http://www.mce-5.com/downloads/MCE-5_2008_GB.mpg
MCE-5 site : http://www.mce-5.com/introduction/index.htm
BMW efficient dynamics : http://bmw.co.uk/bmwuk/efficient_dynamics/bc/homepage
Thesis TDI Spider LM : http://www.fiatlanciathesispidertdilemans.it/ita/home.html
The official MB Photo & Film Site : http://members.chello.nl/m.been6/index/Mijn_albums/Mijn_albums.html
The Apfelbeck 3V project : http://www.apfelbeck.nl/
Jay Leno‟s Garage : http://www.jaylenosgarage.com/video/index.shtml
Jeffrey Smith‟s : http://www.chevyhiperformance.com/techarticles/45618_inductive_cd_ignitions_basics/index.html
Email Francosporto : [email protected]
don‟t hesitate, even for a small question or a tiny suggestion …………………………
- Have fun in reading all of this –
Francosporto™
-/-
Later on I discovered more of the same but different on the ever surprising internet:
http://www.chevyhiperformance.com/techarticles/45618_inductive_cd_ignitions_basics/index.html
Check the Chevy High Performance site or if it‟s not on line anymore read resume below with .... a big thank you to Jeff Smith:
Ignition Basics
By Jeff Smith
“ Inductive versus CD Ignitions”
From the February, 2009 issue of
Chevy High Performance
The ignition is easily the most misunderstood system in any car. Most enthusiasts treat ignitions like some sort of weird, black
magic/voodoo curse best left alone until it fails. Either that or they spend tons of money on parts they may not need. Given the large
body of existing misinformation, we decided to zero in on the two basic types of performance ignitions. We’ll explain how they work and
the advantages of each. While we’ll keep it simple, there is some basic physics here that you’re just going to have to wade through.
Triggering a spark across a spark-plug gap requires both voltage and amperage. Voltage is the electrical pressure that “pushes” the
current (amperage) through a conductor. In order for a spark to jump the gap, a large amount of voltage is required. For a 9:1
compression street engine, this can be between 8,000 and 12,000 volts. But voltage is not what initiates combustion. The voltage
ionizes the air in the plug gap, creating an electrical path across this gap. Once this occurs, the voltage requirement is reduced and
current flows across the gap, creating that blue arc that typifies a strong spark. This current flow of energy across the gap is what
begins the combustion process.
The amount of current flow combined with the voltage plays a big part in an efficient combustion process. The more current pushed
across the plug gap, the better the chance for more complete combustion. As an analogy, it’s tough to light a big log in your fireplace
with a match. It’s much easier with an oxyacetylene torch. In the combustion chamber, the match represents a low-amperage ignition,
while the torch represents a high-amperage system.
Now that we have a grasp on basic combustion, let’s move upstream to the ignition system. There are two basic types of ignitions. The
most common is called inductive discharge, while more performance-oriented ignitions are designed as capacitive-discharge (CD)
systems. Let’s take a closer look at both and compare performance characteristics.
Inductive Discharge
Inductive-discharge ignitions date back to the earliest points-type ignition systems. In its simplest form, this system uses a set of
points to trigger a coil. All coils operate on the same basic principal with a small number of primary windings outside a large number of
secondary windings wrapped around a metal core. The positive side of the coil is connected to battery power while the negative side is
connected to the distributor points and eventually to ground. The high-tension tower lead directs the output of the coil to the distributor
and eventually to the spark plugs. Since points cannot handle a full 12-14 volts, a ballast resistor is used to reduce operating voltage to
6-8 volts and to limit the amount of current passing through the points.
There are generally about 100 times the number of secondary windings to the primary windings in the coil called the turns rat io. When
the points are closed, current flows through the coil, charging the primary windings. The length of time that the points are closed is
called dwell time. When the points open, the current flow is interrupted and the magnetic field created by the current in the primary
windings collapses across the secondary windings, creating a much higher voltage, but at a reduced amperage. Generally, a stock
points-type coil can create as much as 25,000 to 30,000 volts. Even though these coils are capable of this, high-voltage street engines
generally only require about 8,000 to 12,000 volts to ignite the mixture.
The advantage of an inductive ignition system is its simplicity, requiring only a few easy-to-build components. Inductive-discharge
ignitions also deliver a relatively long-duration spark, which is especially good for lighting lean mixtures. The limitation of a pointsswitched inductive system is that the primary side of the system (the points) suffers from low current and voltage. The ballast resistor
is used to lower the current to a level that the points can handle without excessive arcing. When emissions requirements in the ’70s
dictated lean air/fuel mixtures that were more difficult to ignite, GM came up with the High Energy Ignition (HEI). The HEI is still an
inductive-discharge ignition, but it replaces the points with a magnetic pickup and uses a module to regulate the amount of current on
the primary side of the ignition without the need for a ballast resistor. Think of an HEI as an electronic version of a points distributor
with the coil built into the top of the distributor cap.
Time is what handcuffs inductive- discharge ignitions. This system requires dwell time to “charge” the coil up to its maximum capacity.
Think of the inductive system as having to slowly pour water into a glass until it’s full, then dumping the water out when the spark is
required. As rpm increases, there is less time to saturate the coil (fill the glass), which reduces the voltage and current output (the
same as reducing the amount of water in the glass). GM created the HEI as a low-engine-speed emissions-style distributor, so early
HEIs were not designed to generate high voltage and current at high rpm. Therefore, the HEI gained a reputation for “laying down” at
over 5,000 rpm. High-perf HEI modules offer dramatic amperage increases over earlier systems and can now deliver a hot spark
through 7,000 rpm.
Capacitive Discharge (CD)
A CD system is designed to overcome the high-rpm limitations of an inductive-discharge system. In a CD system, alternator voltage
feeds a high-voltage power supply (varying by manufacturer from 450 to 550 volts) connected to a discharge capacitor. When signalled
by the switching device in the distributor, the capacitor applies the 450 to 550 volts to the positive (primary) side of the coil. The coil
transforms this voltage into as much as 30,000 volts, which is applied to the spark plug. Think of the CD ignition as having the capacity
to instantly fill the glass with water before it is dumped out.
A CD spark is much different from an inductive discharge spark. The arc generated at the plug by a CD system is extremely short in
duration, limiting the amount of energy that the spark can deliver. But because a CD system can recharge the capacitor very quickly, it
has the capability to deliver multiple sparks at low engine speeds. A multiple-spark CD system like an MSD, Crane, Jacobs, or Mallory
can fire a spark plug as many as 8 to 12 times per combustion cycle at idle. Unfortunately, as engine speed increases there i s less time
for these multiple strikes. By 3,000 rpm, all multiple-strike systems revert back to single-spark ignitions.
Pros And Cons
The advantage a CD has over an inductive-discharge ignition is that the CD system can produce strong spark energy all the way up to
10,000 rpm. Given the design limitations of an inductive system, this is difficult for an inductive ignition to perform. However, at
conservative street-driven engine speeds, inductive systems deliver a very long duration spark that helps driveability. CD systems
compensate for a short-duration spark with multiple ignition strikes to effectively extend the spark duration.
One way to improve combustion efficiency with any engine is to increase the spark-plug gap. This requires a higher voltage spark,
which can do a better job of igniting the mixture, especially at idle. This comes at the cost of greater demands on the ignition system.
Performance inductive and CD systems can handle larger plug gaps of up to 0.045 to 0.055 inch, but this demands excellent
performance from the entire secondary side of the ignition system (coil wire, cap, rotor, and plug wires) because of the higher voltage
required to jump the wider gap. Typically, this also increases the amperage demands on the ignition system as well.
CD ignitions are virtually a necessity when building supercharged, turbocharged, or nitrous-oxide–injected engines. These engines
create tremendous cylinder pressures that increase the resistance that the ignition faces when lighting the spark. Generally, higher
cylinder pressures require more voltage to initiate the spark. Violent misfires under maximum, high-rpm load in these situations are
often caused by an inadequate ignition system that cannot fire the spark plug because of the resistance caused by the increased
cylinder pressure.
The disadvantages to CD systems are that they are more complex, require more components, and can be more expensive. CD ignitions
also take up more space. These are the main reasons why OEM manufacturers continue to use inductive ignitions. One solution to the
problem of energizing the coil for an inductive system is to create a distributor less, coil-on-plug ignition system such as the one used
on the current-generation LS1 engine. There has been a significant growth in the number of both inductive and CD aftermarket ignition
systems from which to choose. The most popular street CD ignition is the MSD-6A. A few years ago, Crane jumped into the ignition
market with a powerful, multi-strike CD ignition system called the HI-6. Other companies offering CD systems include the 300+ CD
from ACCEL, Holley’s Annihilator line up, Mallory’s several versions of the Hy-Fire VI, Jacobs new FC-1000 box, and others.
Of course, there are plenty of high-performance inductive ignitions as well. The stock HEI distributor can be modified into an excellent
street ignition system with the addition of a matched combination of a high-performance module and coil. Companies like ACCEL,
Performance Distributors, Pertronix, Moroso, and others offer HEI ignitions that work very well. ACCEL, MSD, Crane, Jacobs, and others
also offer add-on boxes that will enhance an inductive-discharge ignition. The best way to improve an inductive system is to get rid of
those ancient points and move up to an electronic distributor. Recently, a couple of companies have added to the CD stockpile by
replacing analogue switching devices with digital technology. These include the new MSD Digital-6 Plus and the Mallory digital multistrike HyFire VI. Of course, as with any digital device, this demands the use of spiral-braided spark-plug wires since solid-core wires will
create enough electromagnetic interference (EMI) to shut down even the best digital devices.
We’ve tried to keep this ignition primer simple to give you an idea of the differences between the inductive-discharge and the
capacitive-discharge systems. Both ignitions offer certain advantages. Understanding the differences makes it much easier to select the
right ignition system (below) for your needs.
Crane Cams
530 Fentress Blvd.
Daytona Beach
FL 32114
(386) 258-6174
www.cranecams.com
Mr. Gasket (ACCEL, Mallory)
Cleveland
OH 44144
Performance Distributors
Memphis
TN
901/396-5782
performancedistributors.com
Holley Performance Products
Bowling Green
KY
270/781-9741
holley.com
Pertronix
San Dimas
CA
909/599-5955
pertronix.com
Jacobs Electronics Inc.
Midland
TX 79701
MSD Ignition (Autotronic Controls Corp.)
1490 Henry Brennan Dr
El Paso
TX 79936
Thanks Jeffrey,
regards Francosporto
--/--