I did have a set of 2 heat range colder plugs in the engine, but found that they were causing a large electrical noise issue becuase they were not resistor plugs.
so, i put my stock resistor plugs back in, NGK FR4 but they are stock heat range. Im getting some breakup in my AFR around 4500 at WOT. I cannot clear it by adding fuel, so i feel its safe to assume at this point the plugs are possibly getting hot and preigniting the mix, cuaseing a disturbed flame front, and uneven burn. no amount of fuel is going to fix this.
so, what plugs should i get???? If i were to go to the parts store right now, and walk up to the counter, what should i ask for EXACTLY to get a plug that is 2 ranges colder, but still a resistor, AND IN STOCK? Brand is irrelevant as long as the other three conditions are true.
Ive seen where people posted other plug numbers to get, but when i go to the part store and ask for them, they look at me like im a lunatic. As if i gave them the brand and model series, but not an actual part number. Please tell me exactly what to ask for so i can go get these ASAP.
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Last edited by nukkinfuttz; 12-05-2008 at 04:19 PM.
for instance, lets say i was told to get a set of NGK FR4
if i asked for "NGK FR4" this would not be enough information, becuase it doesnt include the plug dimentions. I would need a NGK FR4 5155 to indicate its tip style, lenth, etc. so that it will work with my quad 4 and not some other engine with different dimentions, but the same heat range. you see?
The insulator nose length
Gas volume around the insulator nose
The materials/construction of the center electrode and porcelain insulator
The insulator nose length is the distance from the firing tip of the insulator to the point where insulator meets the metal shell. Since the insulator tip is the hottest part of the spark plug, the tip temperature is a primary factor in pre-ignition and fouling. Whether the spark plugs are fitted in a lawnmower, boat, or a race car, the spark plug tip temperature must remain between 500C-850°C. If the tip temperature is lower than 500°C, the insulator area surrounding the center electrode will not be hot enough to burn off carbon and combustion chamber deposits. These accumulated deposits can result in spark plug fouling leading to misfire. If the tip temperature is higher than 850°C the spark plug will overheat which may cause the ceramic around the center electrode to blister and the electrodes to melt. This may lead to pre-ignition/detonation and expensive engine damage. In identical spark plug types, the difference from one heat range to the next is the ability to remove approximately 70°C to 100°C from the combustion chamber. A projected style spark plug firing tip temperature is increased by 10°C to 20°C.
I dont think looking at every plug in the part store is going to be my best bet on getting the correct item today.
stock Quad4 plugs are 431, [RN14YC] for the Champion pn. 1 step colder is [RN12YC], or stock number 71. the 14 and 12 are pretty much the same plug to be honest. a colder plug is the RC9YC. this is the same plug i use in the Barracuda's 360.
specs for the stock plug and the RC12YC are identical: 14mm Thread , 19mm (3/4") Reach, 5/8" (16mm) Hex Size, Gasket Seat, Resistor, Copper Core, Projected Tip.
you SHOULD be able to walk into a parts store and ask for a Champion RC9YC or a NGK FR5. if the parts monkey cant figure it out, ask for someone with a brain. any decent gear head should know plug cross references.
a quick reference is that American Plug mfgs heat ranges get colder as the number DECREASES. EU and JP plugs are exactly the opposite.
each number is a heat range to itself. a 12 is cooler than a 14. both the 12 and 14 can be used in the HO and LO. they are listed as both PNs for each engine.
an 11 is considered 1 step colder. a 10 is colder yet. when using Champion plugs, most people make a 2 step jump in plugs because the heat ranges are so close together than dropping 1 range usually results in no change. thats why you commonly see ppl refer to a rc12yc as 1 step colder than a rc14yc for example.
my advice to you is go start at a RC12YC and go colder from there if you need. drop to a 10 or a 9 if needed. the 12 should work and if it doesnt a 10 will.
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the NGK number u listed has a R in it, that means its a Resistor plug. however, just to be sure, i'd still measure it with a multimeter. set it to OHMs and look for a restance of 5K (5000) ohms.
if they are not resistor plugs, they will read a dead short/ continuity from tip to tip through the plug.
but if i were to get them longer, then they would protrude into the combustion chamber, and not be engaged with the head at that point. so, all the extra threads would do is soak up even more heat from the chamber, but not be able to transfer it away, because its not touching the threads of the head. not to mention what if the valves hit the plug if it where too long and protruding into the chamber. i just dont think thats a good idea at all. sorry.