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

 

Can you tell me why a standard Bosch spark plug does not seem to perform nearly as well, or as long as a standard AC Delco plug of approximately the same price in a Chevy 4.3L engine.
It seems that when these Bosch plugs are installed, numerous drivability concerns appear.

 

There's a few different reasons why plugs in general may opperate differently in a vehicle. Especially, modifications are made to a vehicle, using the plugs required for optimum performance become more imperitive, as well as using the proper gap setting. However, the proper gap setting should be used regardless of whether the vechile is stock, or has a few mods. Another factor is manufacturing - some plug manufacturers have higher standard than others, etc.

In regards to Bosch in particular - I haven't personally used any Bosch plugs, or even looked into the quality of their plugs, so I can't vouch for their quality.

 

bosch platinums suk, with there none gapable 4 electrodes, i never got any worse performance from those plugs. AC Delco all the way! why/how do those 4 electrode plugs compare to the performance of standard plugs, what are the supposed postives of them?

 

Multi-ground plugs (whether they have 2, 3, or 4 electrodes) are also called rotary plugs at times. They are made mostly for rotary engines, and will work very poorly in non-rotary engines. So any multi-ground plug that is featured or pushed for a non-rotary engine is just a marketing ploy. They're trying to get you to think that if one electrode is good, more must be better and that they will last longer. Electricity will follow the path of least resistance, and there will only be one spark at a time, or the plug will only fire off one electrode at a time. And due to the design of the plug, they won't last longer than a traditional plug in a non-rotary engine.

 

A data point relevant to this thread:

Multi-electrode plugs are (or were) recommended by the factory for Audi's turbocharged motors and the 280ZX Turbo motors. Most parts stores don't know this, so you have to dig to find the bcorrect Bosch or NGK numbers. As a result, most of these motors are running single electode plugs and it doesn't really seem to make a perceptible difference in performance.