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Spark Plug Technical Info

Old 12-01-2006, 12:00 PM
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Default Spark Plug Technical Info

As the source for spark plugs, we pride ourselves in the technical spark plug information contained on our website. We enjoy providing that technical information on the forums, so here are some of the common topics and questions in regards to spark plugs. If you have any additional questions, please feel free to ask!

Subject covered by this post:

Basic Spark Plug Construction
How do I cross reference from one brand to another?
What are resistor plugs?
What are V-cut or U-grooved plugs?
Multi-Ground Plugs
What are Fine Wire Plugs?
What Is Platinum?
What Is Iridium?
How long will my iridium plugs last?
Can I use Iridium plugs with nitrous injection?



Basic Spark Plug Construction


Let's start out with the basic construction of a spark plug.


Starting at the top, the TERMINAL can come 3 ways:
stud - some wires are made to fit over plugs that don't have a terminal nut on top, the plug is produced with the terminal nut left off.
solid - the terminal nut is permanent and can not be removed. Used particularly in the motorsport and marine industry when there is a lot of movement and vibration and a removable terminal nut could come loose.
removable - the plug comes with a terminal nut, but it can be removed.


HEX - This is the area your socket grabs when removing or installing plug. For automotive applications, plugs usually come with a 5/8 or 13/16 hex. Vehicles prior to about 1980 allow for a 13/16 hex, most after 1980 only allow 5/8.


SEAT - Plugs are available in a tapered seat or with a gasket. The two are not interchangable - in order to use a plug with a tapered seat, your cylinder heads must have been made specifically for the use of a plug with a tapered seat.


REACH - The plug reach is measured from the seat to the end of the threaded are (do not include ground strap in measurement).


THREAD DIAMETER - Accurate Measurement of the cylinder head or removed plug is necessary to determine the plug diameter, which may range form 8mm to 18mm.


GROUND ELECTRODE - Ground electrodes come in a variety of shapes and sizes. They are also called by a variety of names depending on manufacturer, IE: trapezoid cut ground, tapered cut ground, fine wire ground, angled ground, trimmed side electrode, wedge shaped ground, inverted V-tip ground, cut back ground, etc. All have the same purpose, to reduce quenching and shadowing. Ground straps will be discussed in more detail in future technical threads.


CENTER ELECTRODE - A traditional center electrode is 2.5mm. Manufacturers have improved spark plug performance by creating fine-wire, taper cut, necked down and v-power center electrodes. Each of these will be discussed in further detail in future technical threads.


GAP - A spark plugs’ tip temperature and the voltage necessary to fire the plug are directly affected by the gap setting. Most manufacturers set the gap from the factory for that plugs most popular application. Unfortunately, that plug may have hundreds of applications from automobiles to golf carts. Setting the gap for your particular engine is important as insufficient spark plug gap can cause pre-ignition, detonation and even engine damage. Whereas too much gap can result in a higher rate of misfires, loss of power, plug fouling and poor fuel economy. Even if the preset gap is supposed to match your motor, it is always best to physically check that the gap is adjusted properly for your motor prior to installation as the gap may have been changed during shipping.






How do I cross reference from one brand to another?

From the SparkPlugs.com home page, type the part number you wish to cross-reference from into the "PART NUMBER/CROSS-REFERENCE" box located in the center of the page.
DO NOT include the manufacturers name in the part #, In other words if you are crossing over an AC
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Old 12-06-2006, 12:29 AM
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Default RE: Spark Plug Technical Info

I have a question. You listed the Multi-Ground Plug. The Bosch Platinum +2 and +4 an example of this isn't it? Also I have heard of people having problems with using these plugs in more higher tech engines. Is this true? I have also heard they use more fuel than normal plugs.
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Old 12-06-2006, 12:17 PM
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Default RE: Spark Plug Technical Info

The Bosch Platinum +2 and +4 an example of this isn't it?
That is correct - any spark plug that has multiple ground electrodes.

Also I have heard of people having problems with using these plugs in more higher tech engines. Is this true?
Multi-ground plugs should not be used in engines that are not designed specifically for them. If used in other engines, they will not improve performance, and may run worse than the standard recommended spark plug.

I have also heard they use more fuel than normal plugs.
I'm not sure on that one


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Old 12-06-2006, 04:34 PM
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Default RE: Spark Plug Technical Info

Thank you for answering my questions. Do you know specifically what type of engines are designed for Multi-ground plugs?
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Old 12-06-2006, 05:29 PM
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Default RE: Spark Plug Technical Info

All Rotary engines call for this type of plug, however, there are other engines (for example, some Toyota engines) that are designed for multi-ground plugs and are not rotary engines.

A quick way to check a specific engine: use the make/model/year lookup on our site. Denso and NGK do not recommend multi-ground plugs for engines that do not call for them, even if the plug would fit. So if the results on our site list a multi-ground plug, then you know it's safe to use/recommended.
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Old 12-06-2006, 07:11 PM
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Default RE: Spark Plug Technical Info

I bought some multi-ground plugs from the JC Whitney catalog and used them on my '73 Challenger and never had any problems.
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Old 12-06-2006, 07:48 PM
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Default RE: Spark Plug Technical Info

Thank you for your help.
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