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What are the risks/disadvantages to running a plug that's hotter than recommended for my motor?
some engines its a disadvantage others a advantage

called tuning , give the engine what it wants , be it hotter or colder even the stock plug
.
you got a reason to run a hotter plug , then you'll find out by doing it
 

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A spark plug that is too "hot" can become a spontaneous heat-ignition source. Mildly hot can lead to detonation, hotter gets severe detonation (piston erosion, ring cracking, etc), and hotter still can lead to pre-ignition. Pre-ig - if you're lucky - just blows head gaskets. Even moderate pre-ig can permanently disassemble your engine in one firing stroke.

So, the trick is to have a plug that stays hot enough to clean itself of carbon residue fouling (about 900°F and up for gasoline) at idle and low speeds or light loads. But, it has to be cold enough to not heat-up under load to the point of det or pre-ig (around 1400 to 1800°F depending on fuel blend). For high performance and racing engines (especially ones with radical cams and/or poor low-speed fuel control), the plug heat range is chosen during tuning to avoid damage under high load, and this sometimes means they are cold enough to foul easily at idle and low loads. As fouling accumulates, the engine runs rougher due to misfiring, and is often termed the "plugs loading-up (with fouling)". This is the reason racers often rev their engines a couple times before high-power to "clean the plugs" or "blow it out."

David
 

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A spark plug that is too "hot" can become a spontaneous heat-ignition source. Mildly hot can lead to detonation, hotter gets severe detonation (piston erosion, ring cracking, etc), and hotter still can lead to pre-ignition. Pre-ig - if you're lucky - just blows head gaskets. Even moderate pre-ig can permanently disassemble your engine in one firing stroke.

So, the trick is to have a plug that stays hot enough to clean itself of carbon residue fouling (about 900°F and up for gasoline) at idle and low speeds or light loads. But, it has to be cold enough to not heat-up under load to the point of det or pre-ig (around 1400 to 1800°F depending on fuel blend). For high performance and racing engines (especially ones with radical cams and/or poor low-speed fuel control), the plug heat range is chosen during tuning to avoid damage under high load, and this sometimes means they are cold enough to foul easily at idle and low loads. As fouling accumulates, the engine runs rougher due to misfiring, and is often termed the "plugs loading-up (with fouling)". This is the reason racers often rev their engines a couple times before high-power to "clean the plugs" or "blow it out."

David
not 100% true .
fact is a spark plug heat range can only cause preignition .
 

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not 100% true .

fact is a spark plug heat range can only cause preignition .
Of course you meant to also imply (IMO) correct?

You need to list your FMF CERTIFICATES within your signature so that everyone realizes that all you type is gospel.
 

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not 100% true .
fact is a spark plug heat range can only cause preignition .
I am coming from a pump gas angle here (det-limited fuel), as normally in racing you would use sufficiently higher octane fuel so that det would never occur. In that case, the plugs would theoretically only lead to pre-ig. And, in that case, I would agree.

What I've found in tuning with det-limited fuel - is if fuel and timing are right, and the plugs read any det with signs of electrode overheating, a step or two colder will solve it. That indicates to me the hot plugs are the source of det, much the same way as det is promoted by hot valves - heating of the charge causing det as cylinder pressure rises after ignition. Not so?

David
 

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I am coming from a pump gas angle here (det-limited fuel), as normally in racing you would use sufficiently higher octane fuel so that det would never occur. In that case, the plugs would theoretically only lead to pre-ig. And, in that case, I would agree.

What I've found in tuning with det-limited fuel - is if fuel and timing are right, and the plugs read any det with signs of electrode overheating, a step or two colder will solve it. That indicates to me the hot plugs are the source of det, much the same way as det is promoted by hot valves - heating of the charge causing det as cylinder pressure rises after ignition. Not so?

David
race only engines (very high C/R) , yes , don't use street pump fuel .
they do have different gades of racing fuels .

Now for the street fuel , also have different grades . WHY the multi grades for production cars ?

PSIG , your saying the right fuel for the street engine , a colder plug will cure detonation ? then it would also cure an over advanced timed engine woud'nt it ? to much advance would be preignition in my book .
preign and det. are different
 

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race only engines (very high C/R) , yes , don't use street pump fuel .
they do have different gades of racing fuels .

Now for the street fuel , also have different grades . WHY the multi grades for production cars ?

PSIG , your saying the right fuel for the street engine , a colder plug will cure detonation ? then it would also cure an over advanced timed engine woud'nt it ? to much advance would be preignition in my book .
preign and det. are different
I'm curious what you think of this condition, and why it works this way. Bear with me a moment. My example could be a stock engine or tuning a forced-induction street car on pump gas. I use the FI example as it's very common and the tuning and work-arounds for using the crappy fuel are well established. While tuning, the plugs are read (as they are after every pull) for everything typical, like ignition timing, detonation, pre-ig, overheating, etc. Standard tuning stuff.

While pre-ig and detonation are different, they share some traits. Heat is the common factor. They can also commonly happen in the same stroke. No, colder plugs could not cure an over-advanced condition, as that is plug-fired pre-ignition. Likewise, compression heat alone is not the cause for detonation, else you could start your cold engine with the ignition off. Even diesels normally need a bit of heat to kick things off in the morning.

So, let me propose this scenario:

The engine is right-on with fuel and timing and one-step hotter plugs are installed. In the example I gave, detonation is definitely indicated with aluminum speckling on the plug. But, plugs only cause pre-ignition? So, my thoughts are that the plugs are hotter, but not hot enough to pre-ig. The fresh charge comes flowing into the cylinder, cooling the hot plug. As the plug is cooled, where does the heat go? That's the clue I'm zeroing-in on.

So, the theory is the stream of mix that was cooling the plug is now traveling around the chamber when the plug fires. While the majority of the mix is burning normally and the cylinder pressure rises, that blob of hot mix spontaneously ignites, initiating detonation. Simply switching back to the cooler plugs stops the det and everything is normal.

How does that theory sound? Or, what do you think is different?

David
 

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where does the heat go .. the fuel mix carries some of the heat away .

enought heat away if plug if to (range) hot ... No . center electrode will act as a glow plug . hot plug then ignites fuel .

detonation is from the lack of fuel resisting ignition by static pressure'
reason for higher octane fuels . street cars don't have high compression ratios requiring race fuel , to have different pump grade to match cylinder static psi
fuel octane is aimed at a given static pressure .

to so called run on is preignition .. cause is heat by plugs or carbon , sharp edge and ...... .... . higher octane fuel doesnt cure that problem
 

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I'm curious what you think of this condition, and why it works this way. Bear with me a moment. My example could be a stock engine or tuning a forced-induction street car on pump gas. I use the FI example as it's very common and the tuning and work-arounds for using the crappy fuel are well established. While tuning, the plugs are read (as they are after every pull) for everything typical, like ignition timing, detonation, pre-ig, overheating, etc. Standard tuning stuff.

While pre-ig and detonation are different, they share some traits. Heat is the common factor. They can also commonly happen in the same stroke. No, colder plugs could not cure an over-advanced condition, as that is plug-fired pre-ignition. Likewise, compression heat alone is not the cause for detonation, else you could start your cold engine with the ignition off. Even diesels normally need a bit of heat to kick things off in the morning.

So, let me propose this scenario:

The engine is right-on with fuel and timing and one-step hotter plugs are installed. In the example I gave, detonation is definitely indicated with aluminum speckling on the plug. But, plugs only cause pre-ignition? So, my thoughts are that the plugs are hotter, but not hot enough to pre-ig. The fresh charge comes flowing into the cylinder, cooling the hot plug. As the plug is cooled, where does the heat go? That's the clue I'm zeroing-in on.

So, the theory is the stream of mix that was cooling the plug is now traveling around the chamber when the plug fires. While the majority of the mix is burning normally and the cylinder pressure rises, that blob of hot mix spontaneously ignites, initiating detonation. Simply switching back to the cooler plugs stops the det and everything is normal.

How does that theory sound? Or, what do you think is different?

David
"heat alone " then "a cold engine" . think about your statement on detonation and starting the engine
 

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