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

 

Hi. That was quite an informative read.

Can you explain how using higher grade plugs can increase performance, and what is the overall benefit of spending the extra money for the upgrades? I am very interested to know.

Thanks!!

 

Informative read. I appreciate learning more about Iridiums. Thank you.

I didn't believe the 100,000 mile talk.

Like Bigg J asked, any info on the performance advantage from Iridium to platinums or other plugs is welcome.[8D]


Tj

 

Great read. Where did I miss the 100,000 mile portion? I even searched the page and can't find it and the post hasn't been edited. Are you referring to the 60,000-80,000 on iridium?

 

very good read, now what does everybody use for plugs in there car???


me myself i use NGK,

i know acdelco is meant for the gms, but being in the auto business i get to take a look at all this stuff all the time and was looking at the ac-delco plug that goes in our cars

and right on the base of the plug it says made my NGK, and its the same on quite a few of them, they make some of the champion ones as well

and they are half the price, so its something to think about when your car needs a tune up go with an NGK 3403 plug instead of spending twice the money on the exact same ac-delco plug

i know its hard to get people to see this, a lot of mechanics think that ac-delco goes in gm, autolite in ford, and champion in chrysler. but after having all of these vehicles and putting all these corresponding plugs in all of them, then putting ngk ones in them as well, i know what works better from my own personal experience and i will always be using NGK plugs over anything else on the market

 

Thanks for all the questions, we appreciate the participation!

The info on fine wire plugs and iridium pretty much shows the basics on the advantages of these high performance plugs. But as a summary, Its not solely the iridium metal itself that improves performance. The key to iridium plugs is the fine wire center electrode. The center electrode on traditional (standard nickel) plugs is 2.0mm-2.5mm. The center electrode on iridiums is .7mm(NGK) and .4mm(Denso) - the smaller center electrode requires less voltage to jump the gap, which equates to fewer misfires, which equates the possibility of higher mileage and horsepower. The smaller center electrode also reduces quenching (see the data on fine wire plugs, or http://www.sparkplugs.com/sparkplug4...enching&mfid=0 to learn more about quenching)

In order to create these fine wire plugs, the manufacturers had to start using metals like platinum and iridium, as the nickel wouldn't last long enough. Iridium is about twice as hard and strong as nickel and has a higher melting point.

As far as the longivity of these plugs is concerned, it will vary depending on use. The manufacturers claim you'll see 40-60k miles. On an un-altered motor, under normal use, you should see 60k-80k, and i've used the plugs even longer. I've owned a couple of vehicles that were a royal pain in the butt to change the plugs on (someone on another forum used some line about an extra from Cirque Du Soliel designing the engine compartment - i thoroughly enjoyed the comparison) so anyways, the main selling point for me was the longivity of the plugs.

Hope that answers your questions!

 

Cool. This has been a very informative thread.

 

Would iridium plugs be a worthwhile application for a naturally aspirated 3800 engine?

 

The fundamental operation behind fine wire plugs would still apply. We're running a contest right now to win a set of free iridium plugs, so a MonteCarloForum.com member can try them out and report back on their performance. https://montecarloforum.com/m_20539/tm.htm