The following tips will help you pick your next set of spark plugs.
The key to any upgrade is to do it with a total goal in mind, and consider the other aspects of the car.
Some upgrades will help a lot in one car, and hurt in another car. If you do some thing to help one area, such as low torque, and something
else, say high rpm, the overall effect could be to actually slow the car down. You may hurt the performance in one area, or overall drop.
Bosch plugs: They have less resistance then AC plugs. So the spark at the plug is longer lasting, but cooler. You could have some
very negative effects from the cooler plugs. Hense, the high output coil. Note the two compensate each other for a break even at some rpm,
but at higher rpm the spark may have more duration without fading. By also adding the low resistance wires, the effect is now a better spark
at high rpm.
The low resistance plug or wires alone would cause a cooler spark and would likely hurt performance. The two together without the coil could
make the car a real dog. At low rpm, the plugs could easily foul. The coil alone would have too much power for the stock wires and plugs, and
would cause ignition breakdown and arcing at the wires. This would drop performance. Doing the coil and wires, but not plugs, would make the
spark longer, but the spark temp would raise too much and could damage the spark plugs.
All of these thing vary depending on each component in the combination.
Some coils are bit stronger, and work well with stock components. Some are much stronger, and would fry stock components.
Again, the key is a complete combination that all parts complement each other. It does take some research. Do the homework, learn all you can for
what you want to do, then post the results on our 914 Yahoo Group and see if someone else has done that, and how it worked. Keeping in mind the other person may have a different cam, compression, emissions etc. Nope, it's not easy. The more people you talk to, the better. Don't forget to ask what someone did that did not work.
Basically, most, if not all imported brand spark plugs, while doing the same thing...firing a spark to ignite the fuel charge, are designed somewhat differently and are matched to the plug wires, coil, etc. Domestic cars, particlularly from our era of discussion, were designed to use plugs and wires of somewhat different
specs....resistance, etc. I guess the best thing to do is stick with what the car was designed to use and you can't go wrong. If you're still running points in your distributor, I see no reason to use the exotic plugs...there's no benefit to be had from them.
To further add to your Spark Plug Knowledge Bank…….
Quoted from Otto Stefaner, general product manager, consumer products
on the Bosch web site.
"Every time a spark plug fires, a tiny bit of metal is lost in the electrical discharge. Over time, this can
degrade a plug's performance." "Multiple electrodes and precious metals minimize this degradation from metal transfer."
Other benefits to the multi-electrode design include "Surface air gap technology increases the electrode gap for better ignition, without
increasing the voltage requirement, enabling the production of a larger flame core in the combustion chamber. Tests show that the four-
electrode, platinum-core plugs transfer more energy efficiently to the air/fuel mixture. And plugs with four ground electrodes have up
to 33% better cold restart reliability than conventional plugs,"
The reason is that the multiple ground electrodes in the Bosch Platinum+4 and Platinum+2 series are made from a special, wear-
resistant nickel alloy, enhanced by the addition of yttrium-alloy. Not only do these plugs utilize factory set "surface air gap"
technology that doesn't need gapping prior to installation, the manufacturer also said that the special alloys resist erosion so the
gap maintains its correct setting for the life of the plug.
Bosch's three-digit numbers are a holdover from the early days, when plugs were rated for engines' "indicated mean effective pressure."
But combustion chamber pressures alone soon proved inadequate, for it was found that the thermal load on a plug also depended upon spark
timing, cylinder head cooling and even on the flow of mixture into the cylinder. These factors greatly complicate the business of
assigning plugs thermal ratings. Each spark plug manufacturing firm has its own test procedure, and though there are efforts being made
to bring the whole thing under some international standard no agreement exists today.
On the other hand, there is an enormous amount of mutual product testing being done, and this enables plug manufacturers to offer
accurate cross-brand conversion charts. However, it should be understood that the equivalents are not exact. When plug maker-A's
chart shows "equivalents" from maker-B and maker-C it only means those are the nearest equivalents; they aren't necessarily identical.
This creates a little confusion, and an opportunity: if you think a particular plug is just a hair too hot or too cold, try its
equivalents in other brands. You might hit upon precisely the thermal characteristics you want.
Heat range progression of numbers within a manufacturer's line of plugs may not accurately reflect the extent of the shift toward
hotter or colder thermal grades. It appears that all the companies began with some neat, evenly-spaced arrangement of numbers and heat
ranges, and then had to shuffle everything around to align themselves with reality. Apparently some plugs are thermally biased, hotter or
colder, to make them better suited to particular applications - as when an engine manufacturer is willing to order large volumes of
plugs if they're biased to suit his needs. And if one of a plug maker's best-sellers is biased colder, while the next-warmer thermal
grade is biased a bit hotter, you get a kind of heat-range gap, which can be bridged only by switching brands.
One very useful variation of the standard spark plug has its insulator nose and electrodes extended from its metal shell. The
projected-nose configuration moves the spark gap a bit farther into the combustion chamber, which tends to improve efficiency by
shortening the distance traveled by the flame front and also making the combustion process more regular. But there is a more important
benefit: the projected-nose plug provides, in many engines, what effectively is a broader heat range than you get with the
conventional flush-nose type. The projected nose is more directly exposed to the fire in the combustion chamber, and quickly comes up
to a temperature high enough to burn away fouling deposits after ignition occurs. Then during the subsequent intake phase this plug's
exposed tip is cooled by the swirling air/fuel mixture. In this fashion the higher temperatures existing at full-throttle operating
conditions are to some extent compensated by the greater volume of cooling air, and the net effect is to make the projected-nose plug
better able to cope with the conflicting demands of traffic and highway travel.
The projected-nose plug's effectiveness depends on the pattern of incoming mixture flow. Four-stroke engines often have intake ports
angled to promote turbulence.
If the plug is positioned directly in the path of the intake flow there will
be a large amount of heat removedfrom the plug's tip by this direct air cooling,
and that is
just what you get in most four-cylinder motorcycle engines. Indeed, any hemi-head four-stroke engine gives its plugs' tips quite a useful
blast of cold air during the intake stroke, and we think projected-nose plugs probably should be in wider use in bikes than is the case.
Two-stroke engines can benefit from projected-nose plugs' fouling resistance which they get simply through the sheer length of their
insulator (it's a long way from the center electrode's tip back up to the metal shell). However, the two-stroke's incoming charge doesn't
always do a good job of cooling its plug, and you have to be very cautious in using projected-nose plugs in a 2 stroke.
Some four-stroke hemi-head engines' domed pistons extend up into the combustion chamber too far, at TDC, to leave room for plug tips that
extend inward. This can prevent the use of projected-nose plugs; it's something you check by covering the plug nose with modeling clay,
shaping it so you have a 360-degree electrode contour, and inspecting for signs of contact after you've installed your "clearance" plug and
cranked the engine over a couple of turns.
Limited plug/piston clearance in certain racing engines has prompted plug makers to create the recessed, or retracted gap, configuration.
Champion inadvertently did everyone a great disservice by labeling its retracted-gap design as an "R" plug: people thought the letter
meant "racing" and used the R-series in all kinds of high-performance applications, which was a terrible mistake. Even if an R-plug's heat
range (all are very cold) is right, its gap placement lights the fire back in a hole and the combustion process never is quite as regular
as it should be. The retracted-gap plug exists only because some engines present a clearance problem; it never was intended for use
where conventional or projected-nose plugs can be fitted.
At one time there was a lot of excitement over another unconventionalplug-nose configuration. In the "surface-fire" plug the spark gap was
between the center electrode and the flanged-inward end of the metal shell, and the insulator material filled its interior out almost
flush with the electrode's tip. Surface-fire plugs don't even have a heat range; they run at about the same temperature as the combustion
chamber's walls and are completely immune to overheating. Neither can they cause pre-ignition. These features were stressed at the time of
their introduction, and everyone thought surface-fire plugs were just wonderful. They aren't, because they make their spark too close to
the chamber wall, and require an incredibly powerful, CDI ignition system.
Platinum and gold-palladium alloys can survive the combustion chamber environment as very small wires, and in that rests their great
advantage. Electrons leap away from the tip of a small-diameter, sharp-edged wire far more willingly than from one that's fatter and
rounded. So the fine-wire plug requires less voltage to form a spark than one with conventional electrodes, and the difference becomes
increasingly biased in the former's favor as hours in service accumulate and erosion blunts the iron-alloy electrodes. There are,
of course, drawbacks with precious-metal plugs: they are more expensive, and they are very sensitive to excessive ignition advance.
The overheating you get with too much spark lead effects plugs' center electrodes before it can be detected elsewhere in an engine,
and when subjected to this kind of mistreatment fine-wire electrodes simply melt. In one sense this is a disadvantage, as it means the
ruination of expensive spark plugs. Seen in another way it's a bonus feature: it is better to melt a plug electrode than an engine.
A final variation on the basic spark plug theme you should know about is something NGK calls a "booster gap," and is known at Champion as
an "auxiliary gap." By any name it's an air gap built into a plug's core, and it improves resistance to fouling. Conductor deposits on a
plug's insulator nose tend to bleed off the spark coil's electrical potential as it is trying to build itself up to spark-level strength.
If so much energy is shunted in this way that firing does not occur we say the plug is "fouled." It is possible to clear a lightly fouled
plug by holding the spark lead slightly away from the plug terminal and forcing the spark to jump across an air gap. The air gap works
like a switch, keeping plug and coil disconnected until the ignition system's output voltage rises high enough and is backed by enough
energy to fire the plug even though some of the zap is shunted by the fouling deposits. Mechanics discovered this trick; plug makers have
incorporated it into some of the plugs they sell, and boster/auxiliary gap plugs work really well with an ignition system
strong enough to cope with the added resistance. Such plugs more or less mimic the fast-voltage-rise characteristics of CDI systems - and
offer no advantage used in conjunction with a capacitor-discharge ignition.
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