Spark Plug heat ranges (explained)





Mr Bogus

Trouble Makers Inc.
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#1
Ok, this is not the most common subject but surprisingly enough, not many fully understand what the differences are in spark plug heat ranges.. This is going to be a down and dirty quicky explaination... (some liberty taken on some specifics)

how hot a spark plug is has nothing to do with the "spark" part of the plug..

When changing heat ranges, you are changing the "thermal" aspect of the plugs operating parameters.. IE the plug is "physically" hotter and not a brighter or hotter spark. (seems to be where some confusion lies)

The issue with "too hot" a plug goes right to basics..

If the plug is too hot, it turns into a "glow plug" for lack of better term. The engine A/F mixture will ignite off this "glowing" plug just it can off glowing carbon.. In short "pre-ignition" ouch... Too cold? the plug will carbon up and "foul" (better of the two options, read into that what you want)

Anyway, this heat change is achieved by changing the base electrode dimension..
Longer taller center electrodes make the plug run physically hotter as it is unable to pass as much heat from the plug to the cylinder head. (some also modify the negative electrode too) A gasket or taper fit plug work differently too as does a spark plug not properly torqued. A loose spark plug can overheat and cause damage..

A short stubby fatter center electrode can push more heat down the plug to the body in a shorter amount of time thus making the plug run "cooler"

Reading a "plugs heat range" requires you look at the porcelain insulator and seeing where the color change happens.. (takes a few plugs to understand what you are looking at)

heat_range1.jpg
 

outlawbusa

1 wheel up aero testing
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#6
just happened to be 2 conversations I went through this week was all.. :)

What I do not understand is why some guys loose mileage going to the iridium (or platinum) plugs...
Something funny though...I am a firm believer in the Iridium plugs...went to change them about 400 miles into the break in cycle and the 2008 models came with Iridiums from the factory. I said, too late now...the new ones are going in. Just changed them again last week (a little more than the yearly interval) with 5900 miles.
 
#7
BOGUS SAID If the plug is too hot, it turns into a "glow plug" for lack of better term

I GOT THOSE ON MY WORK TRUCKS WHEN THE LIGHT GOES OFF YOU CRANK IT.
 

djsin

Lily's Daddy
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#8
just happened to be 2 conversations I went through this week was all.. :)

What I do not understand is why some guys loose mileage going to the iridium (or platinum) plugs...
probably because its running so good they are twisting their wrist more often
:poke:
 

Mr Bogus

Trouble Makers Inc.
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#10
Great info...Thanks! :thumbsup:

Here is some more if you want extra info:

Tech Info - Spark Plugs Overview
a very good article, very much more detailed and they did not call me a liar :laugh:

probably because its running so good they are twisting their wrist more often
:poke:
could very well be.... seems to me that either a lightning bolt works or it does not... I have never done any real comparisons on bike motors but never had issues on automotive motors.
 

twotonevert

Member of P.E.A.
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#13
Good information Randy, but I have a question. Why would you change the heat rate on the plugs in our bikes? Does one plug have a performance advantage over another? I have never understood this issue, even when I was dealing the mustangs, some guys ran cooler plugs, blah blah blah, but I dont get it. I understand the thermostat issue and the heat ranges on them, but why the plugs?
 

Spudley

Grippin' and Rippin'
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#14
a very good article, very much more detailed and they did not call me a liar :laugh:


could very well be.... seems to me that either a lightning bolt works or it does not... I have never done any real comparisons on bike motors but never had issues on automotive motors.
"very much more detailed and they did not call me a liar"........why should we ????....or do you just want us to ????..... :oldcool:

Good read thank you..... :super:
 

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