SPARKPLUGS 101
By A-Train
INTRODUCTION
There has been a lot of talk on the subject of spark plugs
and there is a lot of confusion and misinformation. I wrote this report up to
help you pick the right spark plug for your application and understand why.
This report may or may not affect your application.
Lets start with a spark plug. As you know, a spark plug is
the device that is used in an internal combustion engine to ignite the air fuel
mixture in the combustion chambers. A spark plug is threaded into the cylinder
head and protrudes into the cylinder area. It normally has two electrodes which
project into the combustion chamber (cc). When the spark ignites the air/fuel
mixture, the energy expands and forces the piston downward. The ignition system
(which I won't get into at this point) on the 4.6L is either a DIS or E-DIS
system (electronic distributor less ignition incorporated into the later EEC-V
computers). High voltage is passed from an energized coil pack, through spark
plug wires and to the spark plugs. There are a few exceptions to this.
APPLICATIONS
1991-1997 4.6L Crown Vic/Grand Marquis uses spark plug wires
1994-1997 4.6L T-Bird/Cougar uses spark plug wires
1996-1998 4.6L Mustang GT uses spark plug wires
1993-1997 4.6L 32V Mark VIII uses spark plug wires
Of course there are the Town Car and the modular trucks as
well.
Ford eventually went with the coil-on-plug ignition system
for their newer cars. The first production Ford to receive the coil-on-plug
system was the 1996 Taurus SHO. The following vehicles received coil-on-plug as
well.
1998-present 4.6L Crown Victoria/Grand Marquis
1999-present 4.6L Mustang GT
1999, 2001, 2003 4.6L 32V Mustang Cobra ('03 supercharged)
1999-present Lightning 5.4L supercharged
1998 4.6L 32V Mark VIII
There are others on the list, but I feel that covers our
topic range. So moving on, regardless if the system has spark plug wires or
not, it still has coils and spark plugs. The energy released by the coil is
sent through the spark plug to the electrodes. The current then arcs or jumps
the gap between the center electrode and the ground electrode. This ignites the
fuel vapor in the combustion chamber. It is possible for the coil to release up
to 40,000 volts or more. The higher the voltage, the hotter the spark. The
hotter the spark, the better burning it will be and the more power you will
make.
There are many different types of spark plugs. From
retracted gap/tip, regular gap/tip, cut back ground (used in some NASCAR
applications), fine wire electrode, medium wire electrode, projected nose, and
surface gap. I'm sure I left a few out. Now we are going to talk Motorcraft
spark plugs and applications.
Stock 4.6L engines normally use a AWSF-32 plug in either
Copper or Platinum. This is a nominal range for all purposes. The AWSF prefix
letters tell what type of spark plug it is, or it's family. Normally the prefix
tells the thread length, the type of taper, the suppressor type, etc. If you
are interested in the exact meaning of each prefix, pick up a Ford Motorcraft
spark plug specification book. Moving on, the number is always the heat range.
AWSF-62C would be a hot plug. AWSF-2C would be a cold plug. I will get into
heat ranges later on. The suffix in the part number is the type of material the
center electrode is made of and/or the ground electrode. AWSF-32C is copper.
AWSF-32PP is platinum (platinum ground and electrode). Most early 4.6L engines
used copper spark plugs which are fairly standard. First, copper is readily
available and cheaper than other materials.
IGNITIONS
Let me explain the DIS ignition system now. The Ford
DIS/E-DIS system works on a waste spark management. One half of the spark plugs
fire from the center electrode to the ground electrode and the other half fires
from the ground electrode to the center electrode. The EEC fires two spark
plugs simultaneously. One spark plug on the compression stroke uses the
majority of the coils stored energy, the other spark plug on the exhaust stroke
uses very little of the coils stored energy. This is the reason why you see two
numbers for each sparkplug on the coil packs (i.e. 7/6, 4/1, 2/3, 8/5). Those
two spark plugs are connected in series and this is the reason why you found
AWSF-32PG and AWSF-32P plugs in your 1996 and later 4.6L vehicles when changing
spark plugs. Only half of the plugs will wear out faster than the others. Ford
only needed half of the spark plugs to be full platinum, so this was done to
save cost. The replacement for these are AWSF-32PP, or 8 double platinum plugs.
Later on Ford changed their suffix designation on the platinum plugs to
"EE".
MATERIAL TYPES
Materials used for sparkplugs can dramatically alter
longevity, efficiency, power, and even knock sensitivity. We will discuss three
types of materials used today to manufacture spark plugs. The first is Copper,
which is becoming more and more expensive.
Copper melts at 1981 degrees F and that makes it suitable for an
internal combustion engine. It's a great conductor of electricity (second to
silver), heat and can resist corrosion to a point. Copper is very soft and can
be easily drawn into wires. The majority of the spark plugs on the market today
are copper since it is the most economical of the material to use. Nickel is
also used as an alloying material for a copper spark plug. However car makers
have be using platinum plugs in their engines to increase the tune-up
intervals.
Platinum is a precious metal and it is rare, that makes it
more expensive than copper. It melts at 3,200 degrees F. and it is highly
resistant against corrosion. Platinum has a high fuse point with high
electrical resistance. It is also harder than copper, making it very useful for
longevity of a spark plug. Make no mistake, copper is a better conductor than
platinum.
Finally we will discuss Iridium. Iridium, is extremely hard
and brittle material and extremely rare as well. The melting point is 7,466
degrees F. and it is considered the most dense of elements. Iridium is used
solely as an alloying material for platinum. Platinum alloys contains a small
amount of iridium which is much harder than pure platinum.
HEAT RANGES
Heat ranges of a spark plug are often misunderstood and
neglected. The term heat range refers to the relative temperature of the core
nose of the spark plug. "Hot" and "cold" terms refer to the
thermal characteristics of the spark plug or the ability for the spark plug to
remove heat from its firing tip and combustion chamber. A cold spark plug
transfers heat faster from its firing tip into the insulator. This is due to
the shorter insulator nose it has. That helps keep the tip of the plug from
glowing red and accidentally pre-igniting the air/fuel mixture. The heat is
transferred into the cylinder head and engine coolant. A cold plug is used on
high compression engines or extremely high cylinder pressure situations (i.e.
superchargers, nitrous, or turbochargers). A hot spark plug transfers heat from
its firing tip, slowly. The hot sparkplug is used in a low compression engine
to avoid fouling since the combustion chamber temperatures are low.
It is important to remember that a spark plug does not make
heat, it simply removes it acting as a heat exchanger. The way the sparkplug
companies control heat ranges is to normally vary the length of the core nose
or the alloy of the material used in the electrodes. So a hotter plug will have
a longer insulator nose and therefore a long heat transfer path. Cold spark
plugs have a short insulator nose and can transfer heat much faster. A cold
plug reduces the chances of knock, making the engine less knock constrained.
The trade off is fouling. A colder sparkplug is prone to
fouling faster than a hotter one. Let me explain why. A spark plug must reach a
certain temperature for it to burn off any carbon in the combustion chambers.
Also the same applies to fuel. If the plug is to cold, it may not reach it's
cleaning temperature during normal driving and that will cause the plug to
accumulate deposits. If the deposits aren't burned off, the chance for a
misfire or when the air/fuel mixture is not ignited properly or at all, can
occur. Since a hot plug retains more heat before transferring it to the engines
cooling system, it can burn off these deposits more efficiently. Likewise, if a
spark plug is subjected to extreme temperatures that exceed 1,000 degrees C.,
the spark plug can blister and sometimes melt. Just so we are clear, the heat
range of the spark plug has no effect over voltage or resistance required to
jump the gap.
The rule of thumb is
if you beat on the car and go to WOT (wide open throttle) often, you can get by
with one heat range lower. Motorcraft offers an AWSF-22C plug for this. You
effectively dropped one heat range colder than stock. If you have no
modifications that warrant a colder plug, you will not benefit from them. If
you run a supercharger or nitrous oxide, you want to go as low as you can with
the heat range without fouling up. The '99-present 5.4L supercharged Lightnings
use a spark plug two heat ranges colder than stock. The '99-'00 Lightning used
a medium platinum wire electrode plug with full threads. The part number is
AGSF-12EE. I believe the AGSF-12EE plugs have been superceded with the newer
plugs that I'll talk about next. The '01 to present Lightnings used a newly
designed sparkplug with a fine wire platinum/iridium electrode. The part number
is AGSF-12FM1. Again it is two heat ranges colder than stock in the AGSF
family.
If you are running more spark advance via a custom tune or
chip and you have a few more advanced modifications, drop two heat ranges
colder than stock. If you are running a supercharger or nitrous go with
AGSF-12FM1 plugs or AWSFA-12C plugs. The AWSFA-12C plugs are in the AWSF
family. They are two heat ranges colder than stock, medium wire electrode and
copper. These are excellent for performance and very reasonable price wise,
even when you are changing plugs often (which you should do).
Now, the 32V Mark VIII (DOHC) engines have knock sensors
from the factory. The EEC essentially listens to the engine for harmful knock.
Since the onset of knock is lower than a human can ear, the sensor pulls timing
out before you even know anything is happening. So as a very wise man once told
us, these engines are already knock constrained from the factory and are
pulling timing even with premium gasolines with higher octane ratings. So
switching to an AGSF-12FM1 or an AWSFA-12C plug reduces the chances of knock,
therefore the EEC doesn't get a chance to pull spark out. The result is you
gain back lost power and a good amount of it. The plug itself is not
responsible for more power, the spark advance is. Most of the 4.6L SOHC 2V
engines do not have knock sensors so this doesn't apply.
GAP
The term gap means the area between the center electrode and
the ground electrode on a regular type of spark plug. The gap setting on spark
plug is critical in efficiency and power production as well as emissions. All things
being equal, the larger the gap, the more power you can make. Provided the
spark can jump the gap between the electrodes. If this does not occur, you have
a misfire or a dropped cylinder. On the 4.6L 2V engine, the gap should be set
at 0.054" with a stock ignition. That means the space between the
electrodes should be fifty four thousands of an inch. Always set the gap on a
new spark plug when you take it out of the box. They are normally not set to
your vehicles specifications and if not properly set, you will suffer in the
performance department. To determine your specific gap requirements, either
check the VECI sticker under your hood or consult with a Ford Motor Company or
Helm service manual. Use a feeler gage or gap tool to adjust the gap.
Now on a supercharged, nitrous oxide injected or
turbocharged engine, your cylinder pressures are much higher than a naturally
aspirated engine. As cylinder pressure increases, the energy needed to jump the
gap between electrodes does too. Unfortunately, the stock ignition isn't
powerful enough to provide the additional spark voltage required to jump the
gap. Effectively, you are blowing the spark out under boost or when the nitrous
is applied. Most people simply reduce the gap on the spark plug when boost is a
factor in the equation. This means the distance the spark has to jump is
reduced and the resistance has dropped. On the 4.6L engine with 6-10 psi of
boost, you can get away with a gap between 0.035-0.040". More than 10 psi
of boost is pushing the limits of the stock ignition and you really need to
upgrade to a more powerful voltage supply. MSD makes an MSD DIS-4 system to do
just this. The lower the gap setting, the less power you will make though.
Ideally, with a blower, you want to run as close to the stock gap as possible.
This cannot always be done and with the stock 4.6L ignitions it's down right
impossible. There is another solution though.
Denso makes an iridium type sparkplug with a tiny
"u" groove channel in the ground electrode. Some of you smarter types
may have noticed the similarities between the Lightning FM1 plug and the Denso
iridium plugs. The iridium makes the tip of the electrode very hard. The
manufacturers are able to reduce the overall diameter of the center electrode,
making the tip, very thin and to a point. This dramatically reduces the voltage
required to jump the gap. As we all know, electricity flows to the path of
least resistance. So with a larger gap and a supercharged engine, you picked up
power. The power did not come from the spark plug itself, but rather from the
larger gap area that provided a larger flame kernel. The material and electrode
size allowed the plug to be gapped at the stock specifications under extreme
cylinder pressure situations.
A wise man has told us over and over again, use the
Lightning plugs on any supercharged 4.6L or 5.4L engine. Now you understand
why. Not only are they able to transfer heat faster than a stock spark plug,
the newer FM1 plugs can reduce the resistance and reduce the chances of misfires
on a supercharged or nitrous application.
CONCLUSION
Once again. Stock 4.6L spark plugs:
AWSF-32C
AWSF-32PP
One heat range colder than stock:
AWSF-22C (medium wire electrode, copper)
Two heat ranges colder than stock:
AWSFA-12C (medium wire electrode, copper) Application
withheld.
Platinum choices two heat ranges colder than stock:
THESE ARE LIGHTNING EQUIPPED SPARK PLUGS
'99-'00 used AGSF-12EE (medium wire electrode) half thread
'01-present use AGSF-12FM1 (fine wire electrode) full thread
Yes they will work in any 4.6L and 5.4L engine as well as
the older 3.8L Supercoupe engines. Also, these plugs are not to be used as a
band aid for running lower than required octane rated gasoline's in your
engines. That's working against yourself. Go as low as you can with the octane
rating before it pings then move up a step (RON number). You will make the most
power there. Running 100 octane gasoline in your stock '96 Crown Victoria is a
waste of money. If you are running a chip or other means to advance the spark
timing, then you may need to run 93 or higher octane. Combine that with the
colder plugs and a lower temperature thermostat, you have dramatically reduced
the engine from being knock constrained.
Furthermore, the colder plugs DO NOT offer a power increase
by themselves nor do increase/decrease the voltage requirement, durability or
performance, they can help you make more power. A wise old man once told me
about a plug that was two heat ranges colder than stock in the AWSF family. I
found the part number and posted it a few years ago. So here we are full
circle, from the tip of the wise man you can enjoy more power without harmful
detonation.
So the bottom line is, use one heat range colder than stock
if you abuse the car or see WOT often. If you have a chip that adds timing,
drop two heat ranges. This is up to you, but we all agree it's a better
solution to use two heat ranges colder than stock. If you are supercharged or
run nitrous oxide, this is a no-brainer, go with Lightning plugs or AWSFA-12C.
I hope this helps and enjoy.