What is the difference between a normal range spark plug and a hotter plug. How are they designed differently to make one hotter than the other??? I know why you would use one verses the other but can someone explain how they are designed to make one hotter than the other. Thanks Gerald
- Thread starter gmccool
- Start date
Heat range is determined by the length of the path of heat dissipation between the porcelain and the shell. Cold plugs have mire porcelain in contact with the shell, hot plugs have less porcelain in contact. Heat range can also be controlled by the height of the porcelain in the shell.
dr sportster
Well-known Member
Amount electrode sticks out of porcelain .Be very careful running hotter plugs . I have holed pistons
dr sportster
Well-known Member
Should say amount electrode and porcelain stick out together
Mike(NEOhio)
Well-known Member
- Location
- Newbury, Ohio
Not positive but isn't there a gap inside the porcelin too. Wider gap for a hotter plug. It takes a higher voltage to jump.
Geo-TH,In
Well-known Member
When I was in HS and Kawasaki started importing motorcycles a kid bought a 175cc. Put too hot of a plug in MC and leaned out the carb. MC ran great just before he blew a hole in the piston, directly below the plug.
From what little I know, the temp of the plug has to do with the thermal conductivity between the electrode and the outside of the plug, which acts like a heat sink.
From what little I know, the temp of the plug has to do with the thermal conductivity between the electrode and the outside of the plug, which acts like a heat sink.
Steve@Advance
Well-known Member
It's done with heat transfer.
The steel shell transfers heat to the head, serves as a heat sink for the center electrode.
The shorter the porcelain and center electrode, the closer to the heat sink, the better the heat transfer, so the plug runs cooler.
The longer the porcelain and center, the further away from the heat sink, the hotter it runs.
It's a close balancing act, too cold it carbons up, too hot it can turn into a glowing ember. A glowing ember is hot enough to ignite the fuel during the compression stroke, before the plug fires. Not good!!!
That quickly intensifies the cylinder temperature to the point the top of the piston melts!
Now, on a low compression tractor engine that is not likely to happen unless several factors come together, like extreme full throttle engine load, overheating, poor low octane fuel, lean mixture, over advanced timing, carbon build up in the cylinder, and way too hot plugs.
No use pushing your luck though!
The steel shell transfers heat to the head, serves as a heat sink for the center electrode.
The shorter the porcelain and center electrode, the closer to the heat sink, the better the heat transfer, so the plug runs cooler.
The longer the porcelain and center, the further away from the heat sink, the hotter it runs.
It's a close balancing act, too cold it carbons up, too hot it can turn into a glowing ember. A glowing ember is hot enough to ignite the fuel during the compression stroke, before the plug fires. Not good!!!
That quickly intensifies the cylinder temperature to the point the top of the piston melts!
Now, on a low compression tractor engine that is not likely to happen unless several factors come together, like extreme full throttle engine load, overheating, poor low octane fuel, lean mixture, over advanced timing, carbon build up in the cylinder, and way too hot plugs.
No use pushing your luck though!
I run on insulator color and tip hygiene. If tip is burning off contaminants and insulator is tan I am right on. If brown or material disappearing too hot. If wet, too cold. Fuel octane has to do with too hot. A premium fuel is less likely to pre-ignite with a plug running too hot. Detonation that punches holes in pistons can usually be heard if you don't have the radio blaring and will occur on acceleration or load, like passing a car or climbing a hill if in your truck.
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