1. Installing spark plugs - Cars, Trucks, and SUVs
Torque is one of the most critical aspects of spark plug
installation. Torque directly affects the spark plugs' ability to
transfer heat out of the combustion chamber. A spark plug that is
under-torqued will not be fully seated on the cylinder head, hence heat
transfer will be slowed. This will tend to elevate combustion chamber
temperatures to unsafe levels, and pre-ignition and detonation will
usually follow. Serious engine damage is not far behind.
An over-torqued spark plug can suffer from severe stress to the Metal
Shell which in turn can distort the spark plug's inner gas seals or even
cause a hairline fracture to the spark plug's insulator...in either
case, heat transfer can again be slowed and the above mentioned
conditions can occur.
The spark plug holes must always be cleaned prior to installation,
otherwise you may be torquing against dirt or debris and the spark plug
may actually end up under-torqued, even though your torque wrench says
otherwise. Of course, you should only install spark plugs in a cool
engine, because metal expands when its hot and installation may prove
difficult. Proper torque specs for both aluminum and cast iron cylinder
heads are listed below.
|
Spark plug type
|
Thread
Diameter |
Cast
Iron Cylinder Head (lb-ft.) |
Aluminum
Clyinder Head (lb-ft.) |
|
Flat seat type (with gasket)
|
18 ø mm
|
25.3~32.5
|
25.3~32.5
|
| " |
14 ø mm
|
18.0~25.3
|
18.0~21.6
|
| " |
12 ø mm
|
10.8~18.0
|
10.8~14.5
|
| " |
10 ø mm
|
7.2~10.8
|
7.2~8.7
|
| " |
8 ø mm
|
-- |
5.8~7.2
|
|
Conical seat type (without gasket)
|
18 ø mm
|
14.5~21.6
|
14.5~21.6
|
|
Conical seat type (without gasket)
|
14 ø mm
|
10.8~18.0
|
7.2~14.5
|
2. Installing spark plugs - Lawn & Garden Equipment
1. Confirm that the thread reach of the spark plug is the right one
for your engine.
2. Remove the dirt at the gasket seal of the cylinder head.
3. Tighten the spark plug finger tight until the gasket reaches the
cylinder head, then tighten about 1/2-2/3 turn more with a spark plug
wrench. (Taper seat: About 1/16 turn more).
3. Gapping
Since the gap size has a direct affect on the spark plug's tip
temperature and on the voltage necessary to ionize (light) the air/fuel
mixture, careful attention is required. While it is a popular
misconception that plugs are pre-gapped from the factory, the fact
remains that the gap must be adjusted for the vehicle that the spark
plug is intended for. Those with modified engines must remember that a
modified engine with higher compression or forced induction will
typically require a smaller gap settings (to ensure ignitability in
these denser air/fuel mixtures). As a rule, the more power you are
making, the smaller the gap you will need.
A spark plug's voltage requirement is directly proportionate to the
gap size. The larger the gap, the more voltage is needed to bridge the
gap. Most experienced tuners know that opening gaps up to present a
larger spark to the air/fuel mixture maximizes burn efficiency. It is
for this reason that most racers add high power ignition systems. The
added power allows them to open the gap yet still provide a strong
spark.
With this mind, many think the larger the gap the better. In fact,
some aftermarket ignition systems boast that their systems can tolerate
gaps that are extreme. Be wary of such claims. In most cases, the
largest gap you can run may still be smaller than you think.
4. Indexing
This is for racers only !! Indexing refers to a process whereby
auxiliary washers of varying thickness are placed under the spark plug's
shoulder so that when the spark plug is tightened, the gap will point in
the desired direction.
However, without running an engine on a dyno, it is impossible to
gauge which type of indexing works best in your engine. While most
engines like the spark plug's gap open to the intake valve, there are
still other combinations that make more power with the gap pointed
toward the exhaust valve.
In any case, engines with indexed spark plugs will typically make
only a few more horsepower, typically less than 1% of total engine
output. For a 500hp engine, you'd be lucky to get 5hp. While there are
exceptions, the bottom line is that without a dyno, gauging success will
be difficult.
5. Heat Range selection
Let's make this really simple: when you need your engine to run a
little cooler, run a colder plug. When you need your engine to run a
little hotter, run a hotter spark plug. However, NGK strongly cautions
people that going to a hotter spark plug can sometimes mask a serious
symptom of another problem that can lead to engine damage. Be very
careful with heat ranges. Seek professional guidance if you are unsure.
With modified engines (those engines that have increased their
compression) more heat is a by-product of the added power that normally
comes with increased compression. In short, select one heat range colder
for every 75-100 hp you add, or when you significantly raise
compression. Also remember to retard the timing a little and to increase
fuel enrichment and octane. These tips are critical when adding forced
induction (turbos, superchargers or nitrous kits), and failure to
address ALL of these areas will virtually guarantee engine damage.
An engine that has poor oil control can sometimes mask the symptom
temporarily by running a slightly hotter spark plug. While this is a
"Band-Aid" approach, it is one of the only examples of when
and why one would select a hotter spark plug.
6. Using "racing" spark plugs
Be cautious! In reality, most "racing" spark plugs are just
colder heat ranges of the street versions of the spark plug. They don't
provide any more voltage to the spark plug tip! Their internal
construction is no different (in NGK's case, as all of our spark plugs
must conform to the same level of quality controls) than most standard
spark plugs.
There are some exceptions, though. Extremely high compression cars or
those running exotic fuels will have different spark plug requirements
and hence NGK makes spark plugs that are well-suited for these
requirements. They are classified as "specialized spark plugs for
racing applications". Some are built with precious metal alloy tips
for greater durability and the ability to fire in denser or leaner
air/fuel mixtures. However, installing the same spark plugs Kenny
Bernstein uses in his 300+ mph Top Fuel car (running Nitromethane at a
2:1 air/fuel ratio and over 20:1 dynamic compression) in your basically
stock Honda Civic (running 15:1 a/f ratios with roughly 9.5:1
compression) will do nothing for you! In fact, since Kenny's plugs are
fully 4 heat ranges colder, they'd foul out in your Honda in just a few
minutes.
NGK as a company tries to stay clear of saying that a racing spark
plug (or ANY spark plug) will give you large gains in horsepower. While
certain spark plugs are better suited to certain applications (and we're
happy to counsel you in the right direction) we try to tell people that
are looking to "screw in" some cheap horsepower that, in most
cases, spark plugs are not the answer.
To be blunt, when experienced tuners build race motors, they select
their spark plugs for different reasons: to remove heat more
efficiently, provide sufficient spark to completely light all the
air/fuel mixture, to survive the added stresses placed upon a high
performance engine's spark plugs, and to achieve optimum piston-to-plug
clearance.
Some of these "specialized racing plugs" are made with
precious metal alloy center/ground electrodes or fine wire tips or
retracted-nose insulators. Again, these features do not necessarily mean
that the spark plug will allow the engine to make more power, but these
features are what allow the spark plug to survive in these tortuous
conditions. Most racers know screwing in a new set of spark plugs will
not magically "unlock" hidden horsepower.
7. Using high power ignition systems
Many of the more popular aftermarket ignition systems are of the
capacitive discharge type. They store voltage, or accumulate it, until a
point at which a trigger signal allows release of this more powerful
spark. Companies like Mallory, MSD, Crane and Accel, to name a few,
offer such systems.
They affect spark plugs in that they allow the gaps to be opened up
to take advantage of the increased capacity. The theory is that the
larger and the more intense the spark you are able to present to the
air/fuel mixture, the more likely you will be to burn more fuel, and
hence the more power you will make.
We encourage the use of such systems, but only on modified or older
non-computer controlled vehicles.
In reality, computer controlled vehicles do such a good job of
lighting off the air/fuel mixture (as evidenced by the ultra-low
emissions), added ignition capacity would do little to burn more fuel
since the stock configuration is doing such a good job. Older
non-computer controlled vehicles or those that have been modified with
higher compression or boosted (nitrous, turbo, supercharged) engines can
certainly take advantage of a more powerful ignition system.
8. How To Decode Spark Plug Part Numbers
Andre
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